Chapter 12 Flashcards
how do bacteria’s cell division occur?
via Binary Fission
What is Binary Fission?
1.) Cell grows slowly over time.
2.) Uses a similar system as what is use for DNA replication.
3.) Also begins to segregate in two opposite ends of the cell.
4.) Builds a ring a ring proteins around the middle that helps split the cell into two.
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Final Products: two cells that are more or less identical to what you began with.
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What are the different forms of cell division in eukaryotic cells?
- ) Most common: Mitosis
- Meiosis, most commonly used in vertebrate eukaryotes for the production of gametes.
What is Mitosis?
following DNA replication.
- initially you have one linear strand of DNA per chromosome.
- This becomes two linear and identical strands of DNA per chromosome. Via DNA replication.
- Then each strand is placed in a new cell and is more less the same as what you started with.
What is Meiosis?
-Proceeds round of DNA replication.
- Then, there are two subsequent rounds of cell division. And this is without anther round of DNA replication.
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Final Results: You end with half as much DNA as you started with.
How many parts of the cell cycle is cell division?
- 1 part
What is the cell cycle ?
- series of stages that cells go through on their way to dividing.
Describe the chronological events of the cell cycle from its largest part?
- Remember from last exam with the CTC what is a cycle?
G1: longest phase of the cell cycle. It is very important for cells, because they are metabolically active. They are brining in nutrients from the outside etc.
( can be indefinite)
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Following G1—-> The S phase = this stands for DNA Synthesis.
- DNA replication occurs here.
- ——————————————————————————- Next cells enter G2 (not gally floor two silly), but the second gap phase.
- Cells prep for cell division, via cytoskeletal changes and other things.
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Next is the M phase, composed of two different processes: nuclear division (division of the chromosome=mitosis or meiosis).
- followed by cytokinesis = physically splitting the cell in half.
How can a cell enter the resting state?
- They can leave the cell cycle following G1 and are known as G0.
G0 = post mitotic.
What causes cells to move from one phase of the cell cycle to the next?
1.)
Which was the first transition studied in the history of the cell division process?
- G2—> Mitosis/Meiosis (M)
Reasoning: simply, there are so many dramatic and easily/identifiable physically changes to the cell following (M).
Experiment Question presented by that Reedy: is the factors that control the progression of G2-M phase controlled by regulatory molecules in the cytoplasm or Nucleus?
- How did they conduct such an experiment?
- Roe and Johnson did the following: essentially they sucked out cytoplasm from two different cells.
- One cell was in M phase and one cell that was in Interphase, ( any part of the cell cycle rather than M-phase).
- Separately injected these into frog oocyte’s (frog version of the cell in interface).
- This would show if either the cytoplasm of cell in M phase/ interphase could push a cell prematurely into M-phase.
- Results: cytoplasm of cell in the M phase caused the frog oocyte to prematurely enter the M phase.
- Essentially showed biochemist that they need to look in the cytoplasm of the M-phase.
What is interphase?
any part of the cell cycle rather than M-phase
What is Fp55 and what does that hoe do?
- M-phase Promoting factor, cytoplasmic complex of proteins that when fully active, pushes cell from G2 into M phase.
What is MPF composed of?
How do the two work together?
MPF- complex of two different proteins: CDK & Cyclin
- Cyclin: its levels raise and fall, they peak just prior to the transition between G2 and M.
CDK (cyclin dependent kinase)- Stays constant throughout the cell cycle. It is a kinase, so that means it is going to phosphorylate other proteins and change their activity.
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Cyclin regulates kinase.
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- When the cyclin levels peak and when other conditions are right you now have an active complex.
- This active complex phosphorylates the proteins that then trigger the transition from G2-M phase.
T/F there is only one type of cyclin and CDK?
Explain:
MPF is complex of cyclin B and cdk 1.
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- It turns out that there are other key versions of cyclin and CDK at other key transition points in the cell cycle.
How is MPF made active?
- CDK can be phosphorylated on more than one site:
1.) one site must be phosphorylated in order for the cdk to become active.
2.) one site must be phosphorylated for the other cdk to become active.
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So………… MPF is active when: Cdk is phosphorylated on its active site and de-phosphorylated on its in-active site.
- CDK can be phosphorylated on more than one site:
Name the versions of CDK and cyclin at the following transition points:
G1—>S
S—> G2
G2—-> M
G1--->Enter cell cycle (S): cyclin D's + Cdk4 and Cdk6 S---> Early S: cyclin E + Cdk2 late S---> G2: cyclin A + Cdk2 G2--->M: cyclin B/A + Cdk1 ( don't need to know)
What are Cell Cycle Check Points?
- The check points dictate whether or not the cell needs to proceed though the cell cycle.
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G1 check points: decides if the cell is ready to proceed to the S phase. - Is the cell size adequate to continue?
- Are the nutrient levels sufficient?
- Are the right social signals present
- ## Is the DNA in good shape (undamaged)late G2 Check points: decides if the cell is ready to proceed to the M phase.
- Was DNA synthesis successful?
- Is the DNA still undamaged?
- ## Is their active MPF present?M-Phase check point: decides if the cell is ready to proceed to nuclear division.
- Are the chromosomes properly attached to the apparatus that is going to segregate those proteins into the end of the cell prior to cytokinesis?
- ## Did the cell segregation occur appropriately?
- These questions are ask prior to advancing the cell to the next phase in the cell cycle.
What happens if the cell fails to answer the questions needed to move on to the next phase in the cell cycle?
- ) Delay, hopefully the cell can remain in this location for long enough that it can correct what ever needs to be done so it may advance.
- ) If cells cannot be regulated they will be exterminated via Jason Cao’s HorseCock or apoptosis.
How do the differing cell cycle checkpoints work?
- Note: the differences in Cdk and cyclin.
- Note: a cdk must be bonded to the correct cyclin and phosphorylated in the correct locations.
- The cells can regulate Cdk in three ways:
1. ) the cell can produce the wrong cyclin so the cdk has nothing to bind to.
2. ) The cell can produce the things necessary to phosphorylase the inactive site
3. ) The cell can produce the things necessary to de-phosphorylase the active site - The cell can choose to allow for the correct conditions for the Cdk+cyclin to be active and transition cells from one to the next, or it can produce things to make the complex inactive, thus unable to continue to the next stage.
What example did Reedy’s use to emulate the check points?
- two of the conditions necessary for cells to pass the G1 check point.
- Also, The state of the DNA.
- ## G1 check point has the following present to allow for things to continue: Cyclin D’s + Cdk4 & Cdk6.Social Signals: two things necessary: growth factors and mitogens.
- Mitogen: signaling molecules that bind directly to a receptor, thus directly driving progression through the cell cycle.
- Growth factors: signaling molecules that bind directly to receptors that activate a signaling pathway resulting in increased uptake of nutrients from the environment leading and leads increase to increase in nutrient output from the cell.
BOTH ARE NECESSARY: for the cell to move on past the G1 check point.
—————————————————————————– - # 2:There are enzymes in the nucleus that are constantly scanning the chromosome and looking for damaged DNA. If enough of these proteins are present, they phosphorylate a protein (p53).
- p53 is constantly being made and degraded by the cell, but once home boy gets phosphorylated it can longer be degraded like an absolute PUS.
- So now their levels rise..!!!
- p53 pulls up to the nucleus and acts as a transcription factor thus turning on the genes, one of them being p21.
- p21 is a Cdk-i( Cdk inhibitor protein)
- When p21 is produced it binds to the G1 and S phase cyclin and CDK complexes and prevents them from interacting with their target.
What is the stupid key factor of the G1: growth factor signal transduction pathway?
- an enzyme called mTOR is super important for some reasons: it is the master regulator in cell metabolism.
- It can increase the intake of nutrients into cells
- It can increase the rate of glycolysis and other metabolic pathways that use up those nutrients.
- It can increase the Ribosome synthesis.
- mTOR activation is the key to a robust cellular metabolism, and its activation is dependent upon… persistent signaling through growth factor activated signaling pathways.
Discuss the Mitogen pathway, through mitogens activating a signaling pathway that inhibits RB?
- RB finds to an inhibits anther protein called E2F(transcription factor that binds to and activates the genes necessary for the S-phase).
AS LONG AS RB IS BOND TO E2F: the cell will not proceed to the S-phase.
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BUT HOLD UP WAIT A MINUTE……NOW NOW I CAN TASTE EM: if mitogen is present, it will bind to its receptor that causes cascade of shit leading to the activation of the Cyclin D’s + Cdk4 & Cdk6. - Then the activated Cyclin D’s + Cdk4 & Cdk6 pulls up on Rb’s block and phosphorylates the living piss out of it, thus releasing E2F and the cell can now move on.
What is cancer essentially?
it is essentially the loss of that cell cycle regulation.
What is are benign tumor cells?
- tumor where the cells are dividing in an unregulated way, but the cells are dividing in are still located in their original location.
What is are malignant tumor cells?
- Cells that grow in an unregulated fashion but they are spreading dangerously to new locations.
What causes the unregulated growth of tumor cells?
- mutations occur in two types of genes:
1. ) inactivating mutations or loss of function mutations, that are tumor suppressors- stop cell cycle progression(p21).
2. ) proto-oncogenes: genes whose normal function is to promote cell cycle progression (cyclin). - if you have a mutation that causes the oncogene to be active when it shouldn’t be it will promote cancerous growth.
When does the first chromosomal change occur and what happens to the chromosome during this time?
First, we must cover what the chromosomes looked like in the previous phase:
G1: chromosomes were in linear strands
after s-phase: chromosomes now have a complementary strand known as a sister chromatid.
- This attachment occurs at a centromere.
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G2—> M is where they next change occurs: the chromosomes condense, by having the DNA wrap more tightly around the proteins it is associated thus taking up a much smaller volume.
- The condensed forms of chromosomes are important, as they are much easier to move around during the stages of mitosis.
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End of M - phase, sister chromatids separate to create individual chromosomes (not condensed)
What is a replicated state of the chromosome?
- when the og strand and sister chromatid are bound to the centromere.
How many times shorter is the condensed replicated chromosomal form than the OG chromosomes?
- 10,000 times shorter.
How can you tell a cell is in late G2?
- you can see two centrosomes (necessary for spindle apparatus production) .
What is the first indication that the cell has entered mitosis?
What phase is the cell in based on the description given?
- The chromosome has begun to condense, but is still contained within the nuclear envelope.
- ## The microtubules are beginning to reorganize into this bilaterally symmetrical structure, known as the spindle apparatus.Prophase.
What happens in second phase of mitosis and what is it referred to as?
- Prometaphase:
- The nuclear envelope has broken down allowing microtubules form the spindle apparatus to bond to the chromosomes.
- The chromosomes have also finished their condensation at this point.
- The chromosomes point of attachment of the microtubule from one half of the spindle apparatus and a microtubule from the half of the spindle apparatus.
- The place where the chromosomes and microtubules attach is at a complex of proteins, that assemble on the centrosome.
- This creates the Kinetochore- links the microtubule bond centromere to the spindle.
What drives the Prophase and the Prometaphase of mitosis?
What all does the thing driving it do?
- This is driven by MPF.
- Phosphorylate proteins that go on to create the microtubules that reorganize to make the mitotic spindle.
- Proteins involved in the degradation or breakdown of the nuclear envelope.
- Creates proteins that alters how the DNA is packed thus driving chromatin condensation.
- *** Triggers the fragmentation of other organelles (the Golgi and ER), so they can be evenly distributed to each daughter chromatid, this allows for the new strand to be able to rebuild these organelles at the end of the process.
What is the third stage of mitosis known as and what occurs during this stage?
What important thing occurs here?
- Metaphase:
- We know we here when all the chromosomes are lined up in a linear fashion in the middle of the cell.
- Each chromosome is attached to a microtubule from each half of the spindle apparatus.
- 1st M-point check point phase occurs here. ( they don’t continue until what it says above happens)
- Once this has been reached the cell can move on.
What is the fourth stage of mitosis known as and what occurs during this stage?
What important thing occurs here?
- Anaphase:
- The attachments between chromatids break and the microtubules connecting the chromatids to the spindle apparatus shorten.
- Now the chromosomes, in their replicated state, get pulled to opposite ends of the cell.
- This is where the second M phase check point occurs.
- Also, The MPF has to be turned off prior to continuing.
What is the fifth phase in mitosis?
- Telophase:
- The separated chromatids get pulled to the end of the cell where it rebuilds a nuclear envelope around those chromosomes.
- The chromosomes begin to decondense and the spindle apparatuses start decompose.
- Thus signaling the end of the mitosis.
What follows the fifth phase in mitosis?
- 1st phase of Cytokinesis:
- The cytoplasm separating the two independent nuclear envelopes is divided yielding the formation of two daughter cells each with identical sets of chromosomes.
How do chromosomes get moved around during mitosis?
- what are the different types of all the things that allow for movement of chromosomes?
- ## Well not all microtubules are the same.
- The ones connected to the kinetochore, are called kinetochore microtubules.
- The microtubules that project and meet microtubules from the other side near the mid line are known as overlap or interpolar microtubules.
- ## The microtubules that link the spindle apparatus to the periphery of the cell are known as aster microtubules.
- So these different microtubule motor proteins (kinesin and dynein) associate with different regions of
the spinel apparatus to move shit along it.
What do we see if we zoom in on the spindle apparatus?
- a ton of microtubule motor proteins ( kinesin and dynein).
- Now if you go back in your thinker, you’ll remember that these microtubules hydrolyze ATP to move shit along the microtubule or the microtubule relative to something else.
Question from Reedy: During anaphase, how do sister chromatids get yanked apart from each other?
Describe the experiment?
- ## Someone decided doing an experiment would be sick !!!!!
- He tested these theories:
1.) Microtubules shorten at the kinetochore?
2.) Microtubules shorten at the spindle pole?
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Methods: - Live cells were labeled with two florescent dies, 1.) Blue for the DNA. & yellow for the microtubules.
- Fluorescent dyes apparently you can destroy to dye if you hit it with a high enough intensity.
- So they did this when cell just begun anaphase, only on one half. Through the spindle apparatus.
- The light basically creates dark spots in a straight line.
- So they can now be separated in two sections: dark spot to the kinetochore, and dark spot to the spindle pole.
- ## They can then determine which section is shortened following the progression of anaphase.Result: distance of dark spot to the kinetochore shrunk.
In anaphase when the sister chromatids are dragged away from each other how does this happen?
The distance of the kinetochore microtubule is shrunk, and this takes place at the point where the microtubule connects to the chromosome.
How does this happen: The distance of the kinetochore microtubule is shrunk, thus dragging the chromatids to separate ends?
- The kinetochore ring has a kinetochore microtubule projecting through it.
- The ring contains motor proteins, that will be hydrolyzing ATP and using that energy to drag the microtubule connected to the chromatid back to the spindle pole.
- As long as the motor proteins are moving the kinetochore microtubule rope faster than kinetochore microtubules is loosing microtubules…. everything stays attached and everything works out real cool like.
T/F cytokinesis in animal cells and plant cells is the same?
- False,
- in animal cells, actin filaments rearrange and wrap themselves around the cell. This in addition to myosin cross linking allows for the cell to get pinched.
- The point where the pinch occurs is known as the cleavage furrow
- Plants are different because of their rigid cell walls.
- At the end of mitosis in plant microtubules serve as tracks for vesicles that deliver new phospholipids and new cell wall components (cellulose) to essentially create a new cell wall at the midline of the cell.
- This new cell wall at the midline, essentially divides the cell in half = cell plate.
What is the cell plate?
- The new cell wall formed in cytokinesis of plants that divides the cell in two.
