Wednesday, December 12, 2012
Exercise #1 (natsci2/2a)
Laboratory Exercise # 1: Microscope
Purpose: To learn how to maintain and use a binocular microscope.
Procedure:
1. Review the parts of the microscope by reading and performing the
steps listed below under the titles of "Pathway of Light" and "Focusing
of the Microscope".
2. Perform the calculations for Total magnification and Resolving power.
Materials: Microscope, “e” slide and Blood smears (frog,bird, etc.)
Pathway of Light:
1. Light source - on/off switch and intensity knob. The Rheostat knob controls the intensity
of the light coming from the bulb.
2. Condenser - device found above the light source that converges the light beams into a
point so that they can enter the specimen.
a. Knob - raises and lowers the condenser, so that the point of light entering the
specimen can be varied. For most smears the condensers should be all the way in the up
position.
b. Iris Diaphragm Lever/Control - works like the iris of your eye, a muscle that
controls the amount of light entering the eye. It is found within the condenser and a lever is
provided so the amount of light entering the specimen from the condenser can be varied.
For oil magnification this lever should be positioned to allow maximum light to the
specimen.
3. Stage - where the slide is placed and has a central opening to allow light from the
condenser to pass through the specimen.
a. Slide clip - pulling the slide clip towards you allows for the placement of the
slide, flat on the stage.
b. Stage adjustment knobs - this is a double knob found below the stage that
allows for movement of the slide.
1) What does the lower knob do? ____________________
2) What does the upper knob do? ____________________2
4. Objectives - after the light passes through the specimen it then is picked up by the
objectives that are housed within the revolving nosepiece.
a. Revolving nosepiece - allows for the movement of different power objectives
into position over the specimen.
b. Objectives - magnify the image that is received. There are four objectives
housed on the revolving nosepiece. List the magnification of each and it's
designation.
1) _______________________
2) _______________________
3) _______________________
4) _______________________
5. Body tube - light from the objective after being magnified travels through the body tube
and is directed to the ocular by being reflected off a mirror.
6. Ocular - there are two eyepieces or oculars, therefore this microscope is called a
binocular scope. The oculars also have the ability to magnify the image by 10X.
Focusing the Microscope: Using the "e" slide.
1. Look through the oculars using both eyes. You should see only one image, if not adjust
the intrapupillary distance. **Can't see anything! Make sure your light source is on.
a. Intrapupillary Distance Adjustment: Adjust the oculars by sliding them either
closer together or further apart until you see one field of view when using both eyes.
2. Observe the "e" slide before you place it on the stage of the microscope. Record what
you see here:
3. Place the "e" slide on the stage using the stage clip to hold it in position.
4. Rotate the 4X objective into position over the slide.
5. Use the Course Adjustment Knob (gives approximate focus), while not looking
through the oculars to bring the stage as close as possible to the objective. This means
turning the knob towards you.3
6. Looking through the oculars focus the image using the Course Adjustment knob and
slowly turning it away from you. The image should be in almost perfect focus.
7. Any fine-tuning of the focus is accomplished with the Fine Adjustment Knob (Gives
exact focus) while looking through the oculars.
8. Sketch your view of the letter "e" as seen under 4X in the space provided below. Make
sure the letter is in the center of the field of view.
4X Sketch
9. This microscope is parfocal meaning that when you switch to a different objective the
image should remain in perfect focus.
a. Using the revolving nosepiece move the 10X objective into position over the
slide.
b. Use the fine adjustment only, if necessary.
c. Sketch what you observe of the letter "e". Don't move the stage any!!
10X Sketch
d. Move the 40X objective into position. Without moving the stage, again sketch
what you observe of the letter "e".
40X Sketch
e. What happens to the field of view as you increase the power of the objective?
______________________________________
10. Remove the "e" slide from the stage and replace it with a prepared slide.
11. Focus with the 10X objective in place on the edge of the coverslip. You should see a
fuzzy line when it is in focus.
12. Using the stage adjustment knobs, slide into the center of the coverslip and refocus.4
13. Move the revolving nosepiece until it rests between the 40X and the 100X objectives.
Place a drop of immersion oil onto the slide and rotate the 100X objective into the oil.
Don't move the stage while you are putting on the oil!
14. Increase the light intensity and complete focusing with the fine adjustment knob only.
Sketch what you observe below.
Important Calculations:
1. Total Magnification: Remember the image is magnified twice, once by the objective and
second by the ocular. Calculate the total magnification for each objective.
Total Magnification = Ocular power X Objective power
a. Scanning objective (4X): _____________________
b. Low power objective (10X): _____________________
c. High power objective (40X): _____________________
d. Oil immersion objective (100X): _____________________
2. Resolving Power: a numerical measure of the resolution of the lens. The smallest
distance between two objects that the microscope is able to distinguish as two distinct
points.
a. RP = wavelength of light / 2NA
b. Wavelength of light = the distance between two troughs of the light wave, we
will be using the average wavelength of visible light or .55 m
c. NA = the light concentrating power of the objective. This is listed on the side of
the objective after the magnification power.5
d. Calculate the resolving power for each objective.
1) RP of 4X objective = ____________________
2) RP of 10X objective = ____________________
3) RP of 40X objective = ____________________
4) RP of 100X objective = _________________
Questions:
1. Define the following terms that are important to microscopy:
a) Field of view -
b) Parfocal -
c) Resolving power -
d) Binocular -
e) Numerical aperture -
f) Brightfield -
g) Wavelength of light -
2. The student should be able to locate each part of the microscope and give its function.
Arm Base Body Tube
Condenser Condenser knob Course adjustment knob
Fine adjustment knob Iris diaphragm lever/control Light source
Objective Ocular Rheostat
Revolving nosepiece Stage Stage clip
Stage Adjustment knobs
3. If two points of a sample on a slide are 1.15 um apart and you are using the 40X objective with
and N.A. of .85, will you observe two points or a blob?6
4. What is the total magnification of the specimen if you are using a 75X objective?
Monday, November 26, 2012
MITOSIS and MEIOSIS
Cell division is a process by which a cell, called the parent cell, divides into two or more cells, called daughter cells. Cell division is usually a small segment of a larger cell cycle. This type of cell division is known as mitosis, and leaves the daughter cell capable of dividing again. In another type of cell division present only in eukaryotes, called meiosis, a cell is permanently transformed into a gamete and cannot divide again until fertilization.
For simple unicellular organisms such as the amoeba, one cell division is equivalent to reproduction-- an entire new organism is created. On a larger scale, mitotic cell division can create progeny from multicellular organisms, such as plants that grow from cuttings. Cell division also enables sexually reproducing organisms to develop from the one-celled zygote, which itself was produced by cell division from gametes. And after growth, cell division allows for continual renewal and repair of the organism. A human being's body experiences about 10,000 trillion cell divisions in a lifetime.
The primary concern of cell division is the maintenance of the original cell's genome. Before division can occur, the genomic information which is stored in chromosomes must be replicated, and the duplicated genome separated cleanly between cells. A great deal of cellular infrastructure is involved in keeping genomic information consistent between "generations".
Mitosis is the process in which a eukaryotic cell separates the chromosomes in its cell nucleus, into two identical sets in two daughter nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two daughter cells containing roughly equal shares of these cellular components. Mitosis and cytokinesis together define the mitotic (M) phase of the cell cycle - the division of the mother cell into two daughter cells, genetically identical to each other and to their parent cell.
Interphase
The mitotic phase is a relatively short period of the cell cycle. It alternates with the much longer interphase, where the cell prepares itself for cell division. Interphase is therefore not part of mitosis. Interphase is divided into three phases, G1 (first gap), S (synthesis), and G2 (second gap). During all three phases, the cell grows by producing proteins and cytoplasmic organelles. However, chromosomes are replicated only during the S phase. Thus, a cell grows (G1), continues to grow as it duplicates its chromosomes (S), grows more and prepares for mitosis (G2), and divides (M).
Prophase
Normally, the genetic material in the nucleus is in a loosely bundled coil called chromatin. At the onset of prophase, chromatin condenses together into a highly ordered structure called a chromosome. Since the genetic material has already been duplicated earlier in S phase, the replicated chromosomes have two sister chromatids, bound together at the centromere by the cohesion complex. Chromosomes are visible at high magnification through a light microscope.
Close to the nucleus are structures called centrosomes, which are made of a pair of centriole. The centrosome is the coordinating center for the cell's microtubules. A cell inherits a single centrosome at cell division, which replicates before a new mitosis begins, giving a pair of centrosomes. The two centrosomes nucleate microtubules (which may be thought of as cellular ropes or poles) to form the spindle by polymerizing soluble tubulin. Molecular motor proteins then push the centrosomes along these microtubules to opposite side of the cell. Although centrosomes help organize microtubule assembly, they are not essential for the formation of the spindle, since they are absent from plants, and centrosomes are not always used in meiosis.
Each chromosome forms two kinetochores at the centromere, one attached at each chromatid. A kinetochore is a complex protein structure that is analogous to a ring for the microtubule hook; it is the point where microtubules attach themselves to the chromosome. Although the kinetochore structure and function are not fully understood, it is known that it contains some form of molecular motor. When a microtubule connects with the kinetochore, the motor activates, using energy from ATP to "crawl" up the tube toward the originating centrosome. This motor activity, coupled with polymerisation and depolymerisation of microtubules, provides the pulling force necessary to later separate the chromosome's two chromatids.
When the spindle grows to sufficient length, kinetochore microtubules begin searching for kinetochores to attach to. A number of nonkinetochore microtubules find and interact with corresponding nonkinetochore microtubules from the opposite centrosome to form the mitotic spindle. Prometaphase is sometimes considered part of prophase.
Metaphase
As microtubules find and attach to kinetochores in prometaphase, the centromeres of the chromosomes convene along the metaphase plate or equatorial plane, an imaginary line that is equidistant from the two centrosome poles. This even alignment is due to the counterbalance of the pulling powers generated by the opposing kinetochores, analogous to a tug-of-war between people of equal strength. In certain types of cells, chromosomes do not line up at the metaphase plate and instead move back and forth between the poles randomly, only roughly lining up along the midline. Metaphase comes from the Greek μετα meaning "after."
Because proper chromosome separation requires that every kinetochore be attached to a bundle of microtubules (spindle fibres), it is thought that unattached kinetochores generate a signal to prevent premature progression to anaphase without all chromosomes being aligned. The signal creates the mitotic spindle checkpoint.
Anaphase
When every kinetochore is attached to a cluster of microtubules and the chromosomes have lined up along the metaphase plate, the cell proceeds to anaphase (from the Greek ανα meaning “up,” “against,” “back,” or “re-”).
Two events then occur; First, the proteins that bind sister chromatids together are cleaved, allowing them to separate. These sister chromatids, which have now become distinct sister chromosomes, are pulled apart by shortening kinetochore microtubules and move toward the respective centrosomes to which they are attached. Next, the nonkinetochore microtubules elongate, pushing the centrosomes (and the set of chromosomes to which they are attached) apart to opposite ends of the cell. The force that causes the centrosomes to move towards the ends of the cell is still unknown, although there is a theory that suggests that the rapid assembly and breakdown of microtubules may cause this movement.
These two stages are sometimes called early and late anaphase. Early anaphase is usually defined as the separation of the sister chromatids, while late anaphase is the elongation of the microtubules and the microtubules being pulled farther apart. At the end of anaphase, the cell has succeeded in separating identical copies of the genetic material into two distinct populations.
Telophase
Telophase (from the Greek τελος meaning "end") is a reversal of prophase and prometaphase events. It "cleans up" the after effects of mitosis. At telophase, the nonkinetochore microtubules continue to lengthen, elongating the cell even more. Corresponding sister chromosomes attach at opposite ends of the cell. A new nuclear envelope, using fragments of the parent cell's nuclear membrane, forms around each set of separated sister chromosomes. Both sets of chromosomes, now surrounded by new nuclei, unfold back into chromatin. Mitosis is complete, but cell division is not yet complete.
Cytokinesis
Cytokinesis is often mistakenly thought to be the final part of telophase, however cytokinesis is a separate process that begins at the same time as telophase. Cytokinesis is technically not even a phase of mitosis, but rather a separate process, necessary for completing cell division. In animal cells, a cleavage furrow (pinch) containing a contractile ring develops where the metaphase plate used to be, pinching off the separated nuclei. In both animal and plant cells, cell division is also driven by vesicles derived from the Golgi apparatus, which move along microtubules to the middle of the cell. In plants this structure coalesces into a cell plate at the center of the phragmoplast and develops into a cell wall, separating the two nuclei. The phragmoplast is a microtubule structure typical for higher plants, whereas some green algae use a phycoplast microtubule array during cytokinesis. Each daughter cell has a complete copy of the genome of its parent cell. The end of cytokinesis marks the end of the M-phase.
Meiosis is a process of reductional division in which the number of chromosomes per cell is cut in half. In animals, meiosis always results in the formation of gametes, while in other organism it can give rise to spores. The word "meiosis" comes from the Greek verb meiono, meaning "to make small," since it results in a reduction of the chromosome number.
Meiosis-phases
Meiosis I
In meiosis I, the homologous pairs in a diploid cell separate, producing two haploid cells (23 chromosomes, N in humans), so meiosis I is referred to as a reductional division. A regular diploid human cell contains 46 chromosomes and is considered 2N because it contains 23 pairs of homologous chromosomes. However, after meiosis I, although the cell contains 46 chromosomes it is only considered N because later in anaphase I the sister chromatids will remain together as the spindle pulls the pair toward the pole of the new cell. In meiosis II, an equational division similar to mitosis will occur whereby the sister chromatids are finally split, creating a total of 4 haploid cells (23 chromosomes, N) per daughter cell from the first division.
Prophase I
Homologous chromosomes pair (or synapse) and crossing over (or recombination) occurs - a step unique to meiosis. The paired and replicated chromosomes are called bivalents or tetrads, which have two chromosomes and four chromatids, with one chromosome coming from each parent. At this stage, non-sister chromatids may cross-over at points called chiasmata (plural; singular chiasma).
Leptotene
The first stage of prophase I is the leptotene stage, also known as leptonema, from Greek words meaning "thin threads." During this stage, individual chromosomes begin to condense into long strands within the nucleus. However the two sister chromatids are still so tightly bound that they are indistinguishable from one another. The chromosomes in the leptotene stage show a specific arrangement where the telomeres are oriented towards the nuclear membrane. Hence, this stage is called "bouquet stage".
Zygotene
The zygotene stage, also known as zygonema, from Greek words meaning "paired threads," occurs as the chromosomes approximately line up with each other into homologous chromosomes.
Pachytene
The pachytene stage, also known as pachynema, from Greek words meaning "thick threads,"[1] contains the following chromosomal crossover. Nonsister chromatids of homologous chromosomes randomly exchange segments of genetic information over regions of homology. (Sex chromosomes, however, are not wholly identical, and only exchange information over a small region of homology.) Exchange takes place at sites where recombination nodules (the aforementioned chiasmata) have formed. The exchange of information between the non-sister chromatids results in a recombination of information; each chromosome has the complete set of information it had before, and there are no gaps formed as a result of the process. Because the chromosomes cannot be distinguished in the synaptonemal complex, the actual act of crossing over is not perceivable through the microscope.
Diplotene
During the diplotene stage, also known as diplonema, from Greek words meaning "two threads," the synaptonemal complex degrades and homologous chromosomes separate from one another a little. The chromosomes themselves uncoil a bit, allowing some transcription of DNA. However, the homologous chromosomes of each bivalent remain tightly bound at chiasmata, the regions where crossing-over occurred. The chiasmata remain on the chromosomes until they are severed in Anaphase I.
In human fetal oogenesis all developing oocytes develop to this stage and stop before birth. This suspended state is referred to as the dictyotene stage and remains so until puberty. In males, only spermatogonia exist until meiosis begins at puberty.
Diakinesis
Chromosomes condense further during the diakinesis stage, from Greek words meaning "moving through." This is the first point in meiosis where the four parts of the tetrads are actually visible. Sites of crossing over entangle together, effectively overlapping, making chiasmata clearly visible. Other than this observation, the rest of the stage closely resembles prometaphase of mitosis; the nucleoli disappear, the nuclear membrane disintegrates into vesicles, and the meiotic spindle begins to form.
Synchronous processes
During these stages, two centrosomes, containing a pair of centrioles in animal cells, migrate to the two poles of the cell. These centrosomes, which were duplicated during S-phase, function as microtubule organizing centers nucleating microtubules, which are essentially cellular ropes and poles. The microtubules invade the nuclear region after the nuclear envelope disintegrates, attaching to the chromosomes at the kinetochore. The kinetochore functions as a motor, pulling the chromosome along the attached microtubule toward the originating centriole, like a train on a track. There are four kinetochores on each tetrad, but the pair of kinetochores on each sister chromatid fuses and functions as a unit during meiosis I.
Microtubules that attach to the kinetochores are known as kinetochore microtubules. Other microtubules will interact with microtubules from the opposite centriole: these are called nonkinetochore microtubules or polar microtubules. A third type of microtubules, the aster microtubules, radiates from the centrosome into the cytoplasm or contacts components of the membrane skeleton.
Metaphase I
Homologous pairs move together along the metaphase plate: As kinetochore microtubules from both centrioles attach to their respective kinetochores, the homologous chromosomes align along an equatorial plane that bisects the spindle, due to continuous counterbalancing forces exerted on the bivalents by the microtubules emanating from the two kinetochores of homologous chromosomes. The physical basis of the independent assortment of chromosomes is the random orientation of each bivalent along the metaphase plate, with respect to the orientation of the other bivalents along the same equatorial line.
Anaphase I
Kinetochore microtubules shorten, severing the recombination nodules and pulling homologous chromosomes apart. Since each chromosome has only one functional unit of a pair of kinetochores, whole chromosomes are pulled toward opposing poles, forming two haploid sets. Each chromosome still contains a pair of sister chromatids. Nonkinetochore microtubules lengthen, pushing the centrioles farther apart. The cell elongates in preparation for division down the center.
Telophase I
The last meiotic division effectively ends when the chromosomes arrive at the poles. Each daughter cell now has half the number of chromosomes but each chromosome consists of a pair of chromatids. This effect produces a variety of responses from the neuro-synchromatic enzyme, also known as NSE. The microtubules that make up the spindle network disappear, and a new nuclear membrane surrounds each haploid set. The chromosomes uncoil back into chromatin. Cytokinesis, the pinching of the cell membrane in animal cells or the formation of the cell wall in plant cells, occurs, completing the creation of two daughter cells. Sister chromatids remain attached during telophase I.
Cells may enter a period of rest known as interkinesis or interphase II. No DNA replication occurs during this stage.
Meiosis II
Meiosis II is the second part of the meiotic process. Much of the process is similar to mitosis. The end result is production of four haploid cells (23 chromosomes, 1N in humans) from the two haploid cells (23 chromosomes, 1N * each of the chromosomes consisting of two sister chromatids) produced in meiosis I.
Prophase II takes an inversely proportional time compared to telophase I. In this prophase we see the disappearance of the nucleoli and the nuclear envelope again as well as the shortening and thickening of the chromatids. Centrioles move to the polar regions and arrange spindle fibers for the second meiotic division.
In metaphase II, the centromeres contain two kinetochores, that attach to spindle fibers from the centrosomes (centrioles) at each pole. The new equatorial metaphase plate is rotated by 90 degrees when compared to meiosis I, perpendicular to the previous plate.
This is followed by anaphase II, where the centromeres are cleaved, allowing microtubules attached to the kinetochores to pull the sister chromatids apart. The sister chromatids by convention are now called sister chromosomes as they move toward opposing poles.
The process ends with telophase II, which is similar to telophase I, and is marked by uncoiling and lengthening of the chromosomes and the disappearance of the spindle. Nuclear envelopes reform and cleavage or cell wall formation eventually produces a total of four daughter cells, each with a haploid set of chromosomes. Meiosis is now complete.
For simple unicellular organisms such as the amoeba, one cell division is equivalent to reproduction-- an entire new organism is created. On a larger scale, mitotic cell division can create progeny from multicellular organisms, such as plants that grow from cuttings. Cell division also enables sexually reproducing organisms to develop from the one-celled zygote, which itself was produced by cell division from gametes. And after growth, cell division allows for continual renewal and repair of the organism. A human being's body experiences about 10,000 trillion cell divisions in a lifetime.
The primary concern of cell division is the maintenance of the original cell's genome. Before division can occur, the genomic information which is stored in chromosomes must be replicated, and the duplicated genome separated cleanly between cells. A great deal of cellular infrastructure is involved in keeping genomic information consistent between "generations".
Interphase
The mitotic phase is a relatively short period of the cell cycle. It alternates with the much longer interphase, where the cell prepares itself for cell division. Interphase is therefore not part of mitosis. Interphase is divided into three phases, G1 (first gap), S (synthesis), and G2 (second gap). During all three phases, the cell grows by producing proteins and cytoplasmic organelles. However, chromosomes are replicated only during the S phase. Thus, a cell grows (G1), continues to grow as it duplicates its chromosomes (S), grows more and prepares for mitosis (G2), and divides (M).
Prophase
Normally, the genetic material in the nucleus is in a loosely bundled coil called chromatin. At the onset of prophase, chromatin condenses together into a highly ordered structure called a chromosome. Since the genetic material has already been duplicated earlier in S phase, the replicated chromosomes have two sister chromatids, bound together at the centromere by the cohesion complex. Chromosomes are visible at high magnification through a light microscope.
Close to the nucleus are structures called centrosomes, which are made of a pair of centriole. The centrosome is the coordinating center for the cell's microtubules. A cell inherits a single centrosome at cell division, which replicates before a new mitosis begins, giving a pair of centrosomes. The two centrosomes nucleate microtubules (which may be thought of as cellular ropes or poles) to form the spindle by polymerizing soluble tubulin. Molecular motor proteins then push the centrosomes along these microtubules to opposite side of the cell. Although centrosomes help organize microtubule assembly, they are not essential for the formation of the spindle, since they are absent from plants, and centrosomes are not always used in meiosis.
Each chromosome forms two kinetochores at the centromere, one attached at each chromatid. A kinetochore is a complex protein structure that is analogous to a ring for the microtubule hook; it is the point where microtubules attach themselves to the chromosome. Although the kinetochore structure and function are not fully understood, it is known that it contains some form of molecular motor. When a microtubule connects with the kinetochore, the motor activates, using energy from ATP to "crawl" up the tube toward the originating centrosome. This motor activity, coupled with polymerisation and depolymerisation of microtubules, provides the pulling force necessary to later separate the chromosome's two chromatids.
When the spindle grows to sufficient length, kinetochore microtubules begin searching for kinetochores to attach to. A number of nonkinetochore microtubules find and interact with corresponding nonkinetochore microtubules from the opposite centrosome to form the mitotic spindle. Prometaphase is sometimes considered part of prophase.
Metaphase
As microtubules find and attach to kinetochores in prometaphase, the centromeres of the chromosomes convene along the metaphase plate or equatorial plane, an imaginary line that is equidistant from the two centrosome poles. This even alignment is due to the counterbalance of the pulling powers generated by the opposing kinetochores, analogous to a tug-of-war between people of equal strength. In certain types of cells, chromosomes do not line up at the metaphase plate and instead move back and forth between the poles randomly, only roughly lining up along the midline. Metaphase comes from the Greek μετα meaning "after."
Because proper chromosome separation requires that every kinetochore be attached to a bundle of microtubules (spindle fibres), it is thought that unattached kinetochores generate a signal to prevent premature progression to anaphase without all chromosomes being aligned. The signal creates the mitotic spindle checkpoint.
Anaphase
When every kinetochore is attached to a cluster of microtubules and the chromosomes have lined up along the metaphase plate, the cell proceeds to anaphase (from the Greek ανα meaning “up,” “against,” “back,” or “re-”).
Two events then occur; First, the proteins that bind sister chromatids together are cleaved, allowing them to separate. These sister chromatids, which have now become distinct sister chromosomes, are pulled apart by shortening kinetochore microtubules and move toward the respective centrosomes to which they are attached. Next, the nonkinetochore microtubules elongate, pushing the centrosomes (and the set of chromosomes to which they are attached) apart to opposite ends of the cell. The force that causes the centrosomes to move towards the ends of the cell is still unknown, although there is a theory that suggests that the rapid assembly and breakdown of microtubules may cause this movement.
These two stages are sometimes called early and late anaphase. Early anaphase is usually defined as the separation of the sister chromatids, while late anaphase is the elongation of the microtubules and the microtubules being pulled farther apart. At the end of anaphase, the cell has succeeded in separating identical copies of the genetic material into two distinct populations.
Telophase
Telophase (from the Greek τελος meaning "end") is a reversal of prophase and prometaphase events. It "cleans up" the after effects of mitosis. At telophase, the nonkinetochore microtubules continue to lengthen, elongating the cell even more. Corresponding sister chromosomes attach at opposite ends of the cell. A new nuclear envelope, using fragments of the parent cell's nuclear membrane, forms around each set of separated sister chromosomes. Both sets of chromosomes, now surrounded by new nuclei, unfold back into chromatin. Mitosis is complete, but cell division is not yet complete.
Cytokinesis
Cytokinesis is often mistakenly thought to be the final part of telophase, however cytokinesis is a separate process that begins at the same time as telophase. Cytokinesis is technically not even a phase of mitosis, but rather a separate process, necessary for completing cell division. In animal cells, a cleavage furrow (pinch) containing a contractile ring develops where the metaphase plate used to be, pinching off the separated nuclei. In both animal and plant cells, cell division is also driven by vesicles derived from the Golgi apparatus, which move along microtubules to the middle of the cell. In plants this structure coalesces into a cell plate at the center of the phragmoplast and develops into a cell wall, separating the two nuclei. The phragmoplast is a microtubule structure typical for higher plants, whereas some green algae use a phycoplast microtubule array during cytokinesis. Each daughter cell has a complete copy of the genome of its parent cell. The end of cytokinesis marks the end of the M-phase.
Meiosis is a process of reductional division in which the number of chromosomes per cell is cut in half. In animals, meiosis always results in the formation of gametes, while in other organism it can give rise to spores. The word "meiosis" comes from the Greek verb meiono, meaning "to make small," since it results in a reduction of the chromosome number.
Meiosis-phases
Meiosis I
In meiosis I, the homologous pairs in a diploid cell separate, producing two haploid cells (23 chromosomes, N in humans), so meiosis I is referred to as a reductional division. A regular diploid human cell contains 46 chromosomes and is considered 2N because it contains 23 pairs of homologous chromosomes. However, after meiosis I, although the cell contains 46 chromosomes it is only considered N because later in anaphase I the sister chromatids will remain together as the spindle pulls the pair toward the pole of the new cell. In meiosis II, an equational division similar to mitosis will occur whereby the sister chromatids are finally split, creating a total of 4 haploid cells (23 chromosomes, N) per daughter cell from the first division.
Prophase I
Homologous chromosomes pair (or synapse) and crossing over (or recombination) occurs - a step unique to meiosis. The paired and replicated chromosomes are called bivalents or tetrads, which have two chromosomes and four chromatids, with one chromosome coming from each parent. At this stage, non-sister chromatids may cross-over at points called chiasmata (plural; singular chiasma).
Leptotene
The first stage of prophase I is the leptotene stage, also known as leptonema, from Greek words meaning "thin threads." During this stage, individual chromosomes begin to condense into long strands within the nucleus. However the two sister chromatids are still so tightly bound that they are indistinguishable from one another. The chromosomes in the leptotene stage show a specific arrangement where the telomeres are oriented towards the nuclear membrane. Hence, this stage is called "bouquet stage".
Zygotene
The zygotene stage, also known as zygonema, from Greek words meaning "paired threads," occurs as the chromosomes approximately line up with each other into homologous chromosomes.
Pachytene
The pachytene stage, also known as pachynema, from Greek words meaning "thick threads,"[1] contains the following chromosomal crossover. Nonsister chromatids of homologous chromosomes randomly exchange segments of genetic information over regions of homology. (Sex chromosomes, however, are not wholly identical, and only exchange information over a small region of homology.) Exchange takes place at sites where recombination nodules (the aforementioned chiasmata) have formed. The exchange of information between the non-sister chromatids results in a recombination of information; each chromosome has the complete set of information it had before, and there are no gaps formed as a result of the process. Because the chromosomes cannot be distinguished in the synaptonemal complex, the actual act of crossing over is not perceivable through the microscope.
Diplotene
During the diplotene stage, also known as diplonema, from Greek words meaning "two threads," the synaptonemal complex degrades and homologous chromosomes separate from one another a little. The chromosomes themselves uncoil a bit, allowing some transcription of DNA. However, the homologous chromosomes of each bivalent remain tightly bound at chiasmata, the regions where crossing-over occurred. The chiasmata remain on the chromosomes until they are severed in Anaphase I.
In human fetal oogenesis all developing oocytes develop to this stage and stop before birth. This suspended state is referred to as the dictyotene stage and remains so until puberty. In males, only spermatogonia exist until meiosis begins at puberty.
Diakinesis
Chromosomes condense further during the diakinesis stage, from Greek words meaning "moving through." This is the first point in meiosis where the four parts of the tetrads are actually visible. Sites of crossing over entangle together, effectively overlapping, making chiasmata clearly visible. Other than this observation, the rest of the stage closely resembles prometaphase of mitosis; the nucleoli disappear, the nuclear membrane disintegrates into vesicles, and the meiotic spindle begins to form.
Synchronous processes
During these stages, two centrosomes, containing a pair of centrioles in animal cells, migrate to the two poles of the cell. These centrosomes, which were duplicated during S-phase, function as microtubule organizing centers nucleating microtubules, which are essentially cellular ropes and poles. The microtubules invade the nuclear region after the nuclear envelope disintegrates, attaching to the chromosomes at the kinetochore. The kinetochore functions as a motor, pulling the chromosome along the attached microtubule toward the originating centriole, like a train on a track. There are four kinetochores on each tetrad, but the pair of kinetochores on each sister chromatid fuses and functions as a unit during meiosis I.
Microtubules that attach to the kinetochores are known as kinetochore microtubules. Other microtubules will interact with microtubules from the opposite centriole: these are called nonkinetochore microtubules or polar microtubules. A third type of microtubules, the aster microtubules, radiates from the centrosome into the cytoplasm or contacts components of the membrane skeleton.
Metaphase I
Homologous pairs move together along the metaphase plate: As kinetochore microtubules from both centrioles attach to their respective kinetochores, the homologous chromosomes align along an equatorial plane that bisects the spindle, due to continuous counterbalancing forces exerted on the bivalents by the microtubules emanating from the two kinetochores of homologous chromosomes. The physical basis of the independent assortment of chromosomes is the random orientation of each bivalent along the metaphase plate, with respect to the orientation of the other bivalents along the same equatorial line.
Anaphase I
Kinetochore microtubules shorten, severing the recombination nodules and pulling homologous chromosomes apart. Since each chromosome has only one functional unit of a pair of kinetochores, whole chromosomes are pulled toward opposing poles, forming two haploid sets. Each chromosome still contains a pair of sister chromatids. Nonkinetochore microtubules lengthen, pushing the centrioles farther apart. The cell elongates in preparation for division down the center.
Telophase I
The last meiotic division effectively ends when the chromosomes arrive at the poles. Each daughter cell now has half the number of chromosomes but each chromosome consists of a pair of chromatids. This effect produces a variety of responses from the neuro-synchromatic enzyme, also known as NSE. The microtubules that make up the spindle network disappear, and a new nuclear membrane surrounds each haploid set. The chromosomes uncoil back into chromatin. Cytokinesis, the pinching of the cell membrane in animal cells or the formation of the cell wall in plant cells, occurs, completing the creation of two daughter cells. Sister chromatids remain attached during telophase I.
Cells may enter a period of rest known as interkinesis or interphase II. No DNA replication occurs during this stage.
Meiosis II
Meiosis II is the second part of the meiotic process. Much of the process is similar to mitosis. The end result is production of four haploid cells (23 chromosomes, 1N in humans) from the two haploid cells (23 chromosomes, 1N * each of the chromosomes consisting of two sister chromatids) produced in meiosis I.
Prophase II takes an inversely proportional time compared to telophase I. In this prophase we see the disappearance of the nucleoli and the nuclear envelope again as well as the shortening and thickening of the chromatids. Centrioles move to the polar regions and arrange spindle fibers for the second meiotic division.
In metaphase II, the centromeres contain two kinetochores, that attach to spindle fibers from the centrosomes (centrioles) at each pole. The new equatorial metaphase plate is rotated by 90 degrees when compared to meiosis I, perpendicular to the previous plate.
This is followed by anaphase II, where the centromeres are cleaved, allowing microtubules attached to the kinetochores to pull the sister chromatids apart. The sister chromatids by convention are now called sister chromosomes as they move toward opposing poles.
The process ends with telophase II, which is similar to telophase I, and is marked by uncoiling and lengthening of the chromosomes and the disappearance of the spindle. Nuclear envelopes reform and cleavage or cell wall formation eventually produces a total of four daughter cells, each with a haploid set of chromosomes. Meiosis is now complete.
The Cell
A cell is the smallest part of any living thing. There are many parts of a cell. Each part of a cell completes a certain function for the cell.
All cells include the following parts:
Cell Membrane - forms the outer boundary of the cell and allows only certain materials to move into or out of the cell
Cytoplasm - a gel-like material inside the cell; it contains water and nutrients for the cell
Nucleus - directs the activity of a cell; it contains chromosomes with the DNA
Nuclear Membrane - separates the nucleus from the cytoplasm
Endoplasmic Reticulum - moves materials around in the cell
Ribosomes - make protein for the cell
Golgi Bodies - are used for packaging and secreting of energy
Mitochondria - break down food and release energy to the cell
Lysosomes - are chemicals used to digest waste
Vacuoles - are storage areas for the cell
Cytoskeleton - provides the shape of the cell
All cells include the following parts:
Cell Membrane - forms the outer boundary of the cell and allows only certain materials to move into or out of the cell
Cytoplasm - a gel-like material inside the cell; it contains water and nutrients for the cell
Nucleus - directs the activity of a cell; it contains chromosomes with the DNA
Nuclear Membrane - separates the nucleus from the cytoplasm
Endoplasmic Reticulum - moves materials around in the cell
Ribosomes - make protein for the cell
Golgi Bodies - are used for packaging and secreting of energy
Mitochondria - break down food and release energy to the cell
Lysosomes - are chemicals used to digest waste
Vacuoles - are storage areas for the cell
Cytoskeleton - provides the shape of the cell
Organelles in a Plant Cell
Cell Wall - provides structure to the plant cell
Chloroplasts - contain chlorophyll that is make food for the plant cell
Other Parts
Centrioles = Cell organelles that form the spindle apparatus during cell division
Vesicles = Small bubbles of lipid within a cell, used for the transport of materials within the cell and between the outside environment and the cell membrane . Small bladder or sac containing liquid
Wednesday, August 1, 2012
Rocks
Tenacity = resistance of
a mineral to breakage
Malleability = property
to break into fragments
Sectility = property to
be cut into thin shavings
Flexibility = ability to
be bent but does not regain its original shape after removing the stress
Elasticity = property to
be bent and regain its original shape after stress is removed
ROCKS
Petrology = study of
rocks
I.
IGNEOUS ROCKS = rocks formed by solidification
of magma or lava materials
Types of Igneous Rocks
1.
Volcanic (extrusive)
=originated
from lava
=fast rate
of cooling
=small
sized mineral grains
=fine rock
texture (Aphanitic)
Extrusive Igneous Rocks =
affected by viscosity (resistance to flow)
Factors Affecting
Viscosity
a.
Temperature of lava
=Lava
T>>Solidification T, less viscous
b.
Silica Content of lava
Maffic =
low silica (~50%), flows easily, dark colored
Felsic =
high silica (>65%), flows sluggishly, light colored
Texture of Extrusive
Igneous Rock
a.
Aphanitic
b.
Obsidian = volcanic glass
c.
Porphorytic = large crystals enclosed in a
matrix of much finer-grained minerals
d.
Vesicular = holes are trapped in rock when lava
solidifies while gas is bubbling through it
e. Pumise = Cooled viscous lava where the gas can’t escape easily, and lava is churned
into froth
2.
Plutonic (intrusive)
=from
lava
=slow
rate of cooling
=large
sized mineral grains
=coarse
rock texture (Phaneritic)
Intrusive Igneous Rock
a.
Shallow intrusive rocks
i.
Volcanic neck = formed from magma that
solidified within the throat of volcano
ii.
Dike = tabular, disconcordant (body not parallel
to any layering in the country rock)
iii.
Sill = tabular, concordant (body parallel to any
layering in the country rock)
iv.
Laccolith = concordant with thick central
portion and domes upward like a mushroom
b.
Deep intrusive rocks
i.
Pluton = crystallized at considerable depth,
irregular in shape
ii.
Stock = small disconcordant pluton wit an
outcrop area of less than 100 sq. km.
iii.
Batholith = large disconcordant pluton with an
outcrop area greater than 100 sq. km.
Weathering = mechanical
disintegration and chemical decomposition upon exposure to surface conditions
= very slow process
= disintegration of rock
formations
a. Physical
Weathering = fragmentation of rocks without change in its mineral composition
Factors
=> frost wedging, plants and animals, salt crystals, pressure release, wind,
wave action, abrasion, moving glaciers
b. Chemical
Weathering = Chemical decomposition of rocks
Factors
=> water (hydrolysis), oxygen, acids
Sediments = product of
weathering
= sometimes referred to as regolith
Agents of Sediment
Transportation
=gravity, run-off, rivers and streams, wind, waves,
glacial ice
Traction = process of
transporting coarse sediments along the bottom of stream by rolling/sliding
Saltation = movement of
sediment along of series of leaps
Rounding = grinding away
of sharp edges and corners of rock fragments during transportation
Sorting = process in
which sediment grains are selected and separated according to grain size, grain
shape or specific gravity
Deposition = when
material settles or comes to rest
= accumulation of chemical or organic sediments
II.
SEDIMENTARY ROCKS = formed by lithification of
sediments
Sediment Particles
>256 mm = Boulder
64-256 mm = Cobble
2-64 mm = Pebble
0.02-2 mm = Sand
0.002-0.02 mm = Silt
<0.002 mm = Clay
Boulder + cobble + pebble
= gravel
Silt + clay = mud
Lithification = group of
processes that convert loose sediments into sedimentary rocks
a.
Compaction = packing together of loose grains
tightly
b.
Cementation = precipitation of cement around
sediment grains binding them into a firm rock
c. Crystallization
= solidification of minerals form solution
Types of Sedimentary
Rocks
a.
Clastic = formed from lithification of sediments
that are fragments of pre-existing rocks
i.
Breccia = coarse-grained formed by cementation
or coarse, angular fragments of rubble
ii.
Conglomerate = coarse-grained formed by
cementation of rounded gravel
iii.
Sandstone = coarse-grained formed by cementation
of sand grains
iv.
Shale = fine-grained formed by cementation of
both silt and clay
v.
Mudstone = fine-grained formed by cementation of
clay
vi.
Siltstone = fine-grained from silt
b.
Organic = rocks that accumulate from the remains
of organisms
i.
Coquina = cementation of shells that accumulated
on the sea floor
ii.
Limestone = formed from coral reefs
c.
Chemical = from chemical precipitation
i.
Evaporites = from crystals that precipitate
during evaporation of sea or saline water
d.
Others
i.
Chert = hard, compact, fine grained formed
entirely from silica
ii.
Coal = from solidification of plant materials
Sedimentary Structures
a.
Cross bed = series of thin, inclined layers
within a larger bed of rock
b.
Graded bed = layer in which sizes vary gradually
from coarse grains at the bottom of the bed to progressively finer grains
toward the top
c.
Mud cracks = polygonal patterns of cracks formed
in very fine-grained sediment as it dries
d.
Ripple marks = small ridges on the surface of a
sediment layer by moving wind of water
e. Fossils
= traces of plants or animals preserved in rock
Bedding
= series of visible layers within the rock
3. METAMORPHIC
ROCKS
Metamorphism =
solid-state transformation of pre-existing rock into texturally or
mineralogically distinct new rock as a result of high temperature, high
pressure or both
a.
Contact (Thermal) Metamorphism = Temperature as
dominant factor
= non-foliated rocks
= heat comes from intruding magma
b.
Regional (Dynamothermal) Metamorphism = High
Temp and pressure
= deformed mountains
= large regions in continents
c. Progressive
Metamorphism = progressively greater T and P act on a rock with increasing
depth in the earth’s crust
Factors Affecting
Characteristics of Metamorphic Rocks
a.
Parent Rock = based on chemical composition
b.
Temperature = takes place above 200OC
c.
Pressure
1.
Confining pressure = pressure applied equally on
all surfaces of a body
2.
Directed pressure = pressure applied unequally
on the surface of the body
i.
Compressive Direct Pressure = squeezing pressure
on both sides
= flattens object perpendicular to applied
pressure
ii.
Shearing Directed Pressure = parts of a body
move or slide to one another
= flattens object parallel to the forces
exerted
d.
Foliation = parallel arrangement of the textural
or structural features of rocks
1.
Foliated
i.
Slate = fine-grained rock that splits easily
along flat parallel planes
ii.
Schist = fine-grained with visible platy or
needle-like structures
iii.
Gneiss = rock consisting of light and dark
mineral layers
2.
Non-Foliated
i.
Phyllite = rock in which newly formed micas are
larger than slate but can’t be seen by the naked eye
ii.
Migmatite = mixed igneous and metamorphic rocks
iii.
Marble = derived from limestone
e.
Fluids
f.
Time
Monday, July 23, 2012
minerals
Mineral Classification
The
Dana System
Mineral
classification can be an organizational nightmare. With over 3,000
different types of minerals a system is needed to make sense of them all.
Mineralogists group minerals into families based on their chemical composition.
There are different grouping systems in use but the Dana system is the most
commonly used. This system was devised by Professor James Dana of Yale University
way back in 1848. The Dana system divides minerals into eight basic classes.
The classes are:
Mineral Classification
|
|
 |
Native Elements This is the category of the
pure. Most minerals are made up of combinations of chemical elements. In this
group a single element like the copper shown here are found in a naturally
pure form.
|
 |
Silicates This is the largest group of
minerals. Silicates are made from metals combined with silicon and oxygen.
There are more silicates than all other minerals put together.The mica on the
left is a member of this group.
|
 |
Oxides Oxides form from the combination of
a metal with oxygen. This group ranges from dull ores like bauxite to gems
like rubies and sapphires. The magnetite pictured to the left is a member of
this group.
|
 |
Sulfides Sulfides are made of compounds of
sulfur usually with a metal. They tend to be heavy and brittle. Several
important metal ores come from this group like the pyrite pictured here that
is an iron ore.
|
 |
Slufates are made of compounds of sulfur
combined with metals and oxygen. It is a large group of minerals that tend to
be soft, and translucent like this barite.
|
 |
Halides form from halogen elements like
chlorine, bromine, fluorine, and iodine combined with metallic elements. They
are very soft and easily dissolved in water. Halite is a well known example
of this group. Its chemical formula is NaCl or sodium chloride commonly known
as table salt.
|
 |
Carbonates are a group of minerals made of
carbon, oxygen, and a metallic element. This calcite known as calcium
carbonate is the most common of the carbonate group.
|
 |
Phosphates are not as common in occurrence
as the other families of minerals. They are often formed when other minerals
are broken down by weathering. They are often brightly colored.
|
 |
Mineraloid is the term used for those
substances that do not fit neatly into one of these eight classes. Opal, jet,
amber, and mother of pearl all belong to the mineraloids.
|
BASIC DEFINITIONS
A mineral is a
naturally occurring inorganic substance with a characteristic chemical
composition and definite crystal structure. The composition and crystalline
structure determines the properties of a mineral. The main mineral properties
used for identification are color, streak, hardness, specific gravity, cleavage
and fracture. Other properties such as luster and habit are also important.
Rocks
are aggregates of minerals. Rocks exhibit not only different mixture of
minerals, but also certain textures. The texture depends upon the size, shape,
and arrangement of the minerals composing the rock. Mineral assemblage and
texture serve in determining the origin and identification of a rock.
MINERAL IDENTIFICATION PROCESS
MINERAL IDENTIFICATION PROCESS
MINERAL PROPERTIES
COLOR - The color of a
mineral serves to narrow down the number
of possible choices since it is the first and most obvious
property noticed. However, because most minerals may
exhibit a variety of colors, color is not a reliable diagnostic
property.
of possible choices since it is the first and most obvious
property noticed. However, because most minerals may
exhibit a variety of colors, color is not a reliable diagnostic
property.
HARDNESS - Hardness is a measure
of resistance to scratching. The hardness of a mineral is based upon
comparisons of scratching tests. Mohs Scale of Hardness is the basic comparison
test.
Mohs Hardness Scale
Hardness of Test Materials
1 - Talc 2.5 -
Fingernail
2 - Gypsum 3.5 - Copper penny
3 - Calcite 5.5 - Masonry nail
4 - Fluorite 5.5 - Glass
5 - Apatite
6 - Orthoclase feldspar
7 - Quartz
8 - Topaz
9 - Corrundum
10 - Diamond
2 - Gypsum 3.5 - Copper penny
3 - Calcite 5.5 - Masonry nail
4 - Fluorite 5.5 - Glass
5 - Apatite
6 - Orthoclase feldspar
7 - Quartz
8 - Topaz
9 - Corrundum
10 - Diamond
Example of hardness
determination: If an unknown mineral cannot be scratched by a masonry nail but
can be scratched by orthoclase feldspar, then the hardness of the unknown
mineral would be between 5.6 and 5.9.
STREAK - The color of the
powder of a mineral is the streak. Rub the mineral on a piece of unglazed
porcelain (streak plate) to obtain the streak.
CLEAVAGE - Certain minerals
have a tendency to part, producing smooth flat surfaces. An example is mica: it
cleaves along one plane thus it has one direction of cleavage. Galena
FRACTURE - If a crystal
does not break along a cleavage surface, it exhibits fracture. Quartz shows no
cleavage when it is broken, instead it fractures in a shell shape known as
conchoidal fracture. Other minerals with well-developed cleavage may fracture
along other surfaces. Common descriptions: conchoidal, splintery, fibrous and
irregular.
LUSTER - The degree or
manner in which the surface of a mineral reflects light is luster. Terms used
to describe luster include earthy, glossy, metallic, pearly, greasy, waxy, and
vitreous (glassy).
SPECIFIC GRAVITY - The weight of a
mineral compared to the weight of an equal volume of water is the specific
gravity. Gold has a specific gravity of 19. This indicates that a cubic
centimeter of gold weighs 19 times as much as a cubic centimeter of water. (One
cubic centimeter of water weighs 1.0 grams) A relative comparison (of what is
light and what is heavy) is satisfactory for this laboratory.
ex 2 eratosthenes
Eratosthenes
Purpose
Students will find
the circumference of a wheel (or globe) directly and indirectly, and compare
their results.
Students will prove
if the claims of Eratostehenes are true.
Materials
Wheel (or small globe or ball)
Ruler
Protractor
Paper and pencil
Directions
1. First Method:
a. Placing the wheel
(or globe) with the center on the paper near one edge, draw the
outline of the circle
on the page, marking the center.
b. Draw a radius line
from the center mark to the outside of the circle and ~3 cm
beyond. This line
represents a building standing perpendicular to the horizon at that
point on the circle.
c. Draw a second
radius line from the center perpendicular to the first radius.
This line can
represent a well that is perpendicular to the horizon at another point on
the circle.
e. Use the ruler to
measure the distance (s) along the circle between the two lines.
f. Measure the
circumference (TV). Then compare to the C using the formula below.
C = 360°/(s*90)
2. Second Method:
a. Use the ruler to
measure the diameter (d) of the wheel (or globe).
b. Use the formula C=Π∗d to
calculate the circumference of the wheel.
3. Third Method: Use
a tape measure wrapped around the wheel (or globe) to find the circumference.
4. Using any measuring device, measure the height of
one of your group mate (TV). Measure the shadow casted by your group mate (x),
then calculate for the height (h) which will be your observed value.
h
= x/sin ɵ
Where ɵ is: 30 if 1 pm or 11 am
60 If 2 pm or 10 am
90 If 3 pm or 9 am
120 If 4pm or 8 am
150 If 5 pm or 7 am
Table
2.1 Measured Dimensions of a circle
|
Circular
Object
|
A
(angle)
|
S
(side)
|
D
(diameter)
|
|
|
|
|
|
Table
2.2 Comparative Data of The Calculated Circumference Using Different Methods
|
Method
Used
|
Circumference
|
%
Error
|
|
First
|
|
|
|
Second
|
|
|
|
Third
|
|
|
|
|
|
|
Table
2.3 Comparison of Actual Height Using Shadow
|
Time
|
Actual
height (TV)
|
Shadow
Height (x)
|
Calculated
Height (h)
|
%
Error
|
|
|
|
|
|
|
Guide
Questions
1. Compare your
values for all three measurements/calculations.
2. Using the result
of your third method as the true value, find the % error of each method.
3. What is the claim
of Eratosthenes? Why would Eratosthenes' method not work if the earth were
flat?
4. Why is it
important that we assume that the Sun's rays arrive in parallel on the Earth?
5. How would your
calculated circumference change if you measured the angle larger than it really
is?
6. How would your
calculated circumference change if you measured the angle smaller than it really
is?
7. What could account for errors in your value?
Evaluate your methods and brainstorm ideas for
improving your
results.
Rlp2009
Subscribe to:
Posts (Atom)