I know some of these might be confusing but your help will really help me learn.
ID: 301116 • Letter: I
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I know some of these might be confusing but your help will really help me learn. The teacher requires very very detailed answers and he gives nearly no (and I mean literally nearly zero) partial credit so I'm dying here. Thank you sooooooo much, you have no idea.
Also, I am nearly leaglly blind and I am dyslexic so if you could please write clear it would help so much. I just want to learn like everyone else. SUPER SUPER THANK YOU.
Question 3 Part 1 [9 pts] The eukaryotic cell cycle is very strictly regulated with multiple checkpoints that prevent the cell cycle from continuing if certain conditions are not met A. For each of the following checkpoints, describe a condition in which cells are blocked from progressing past the checkpoint. Then, explain why each of these checkpoints is important for the cell. [2 pt each] Restriction (R) point Post-replication checkpoints Spindle assembly checkpoint B. However, when the appropriate conditions are met, the cell can advance past these checkpoints. For the R checkpoint, this requires phosphorylation of the Rb protein. How is this post-translational modification of Rb similar to the allosteric regulation we have previously discussed? How might this lead to a change in the function of a phosphorylated protein? How does the nature of a phosphate group play a role in this process? [3 pt]Explanation / Answer
Ans1. Restriction checkpoint: It is also called G1 checkpoint. It is the first and the most important checkpoint of cell division. This is the primary stage at which cell decides whether it has to divide or not. If a cell passes this checkpoint then it is irreversible process and it enters the S phase and undergoes next division process.
Cell division blocks at this stage if there is DNA damage, or some other replication errors in the DNA. At this stage any internal or external factors like cell size/volume ratio, nutrient availability, molecular signals correct transduction is responsible top check the cell division at this stage. Any discrepancy in these factors leads to the blocked cell division at restriction checkpoint.
Post Replication checkpoint: Before undergoing to Mitosis phase of cell cycle, there is a post-replication checkpoint also known as G2 checkpoint which ensures whether the replication is done properly or the completeness of the replication process of cell division. It allows cell to pass this checkpoint only after the proper integrity of DNA without any damage and after the complete DNA copies formed in S phase.
If there is any DNA damage in the new strand or there is incomplete replication process due to unavailability of any replication factor, the post replication checkpoint halts the cell division at this stage for repair, or to attempt the complete DNA replication. And If the damage is irreparable cell undergoes apoptosis.
Spindle assembly checkpoint: It is also known as M checkpoint. It looks for correctness of the sister chromatids to be attached correctly with the spindle microtubules, as the detachment or separation of sister chromatids during metaphase is irreparable and the cell cycle will not be completed. So it is mandatory to ensure that the sister chromatids are attached to at least two spindle fibers from opposite poles of the cell.
This checkpoints looks for or scan any looses or staggered chromosome floating in the cytoplasm and confirms that every chromosome is placed properly on the metaphase plate. If there is misplacement of the chromosome then the mitosis will halts and allow the spindle to place the stray chromosome on the metaphase plate properly.
2. Retinoblastoma Rb protein is a unique protein similar to an allosteric enzyme as it has multiple binding and phosphorylation sites. It seems to bind and restrict E2F targets. It has many pockets for binding of various proteins as well as total of 15 possible phosphorylation sites. This is how it regulates the cell cycle at restriction checkpoint. As in the phosphorylated form it passes the R checkpoint and allows the cell division.
3. a. This data suggests that the mutation in which the amino acid is replaced by an amino acid with different acidity or pI value shows different character like Lys replaced by Leu or Glu.
While, that one in which Lys is replaced by Arg having same basic character, have shown similarity in their character as seen in the diagram.
B. The outcome of the experiment in which we have inserted the wild type sequence in the wild type without removing wild type signal will look like wild type only as the signals allow only wild type sequence to get transferred in the next generation after successfully passing the checkpoints.