Instructions: Answer each of the questions given below in your own words. Write
ID: 85281 • Letter: I
Question
Instructions: Answer each of the questions given below in your own words. Write in complete sentences where appropriate. A complete answer usually requires one to two sentences per mark, so a three-mark question would be answered in three to six sentences. This section is worth a total of 40 marks. (4 marks)
1. Explain how CDKs regulate cell division. (4 marks)
2. Explain the role of transposable elements in eukaryotes. (8 marks)
3. Using the following DNA template strand sequence, answer the questions that follow: 3’–TGCAGGAAGCTACATTAG–5’ a. What is the mRNA sequence? b. What is the final sequence of amino acids in the peptide produced? c. If the sequence is mutated so that adenine at position 11 is replaced with uracil, how will the peptide be affected? What kind of a mutation is this? (5 marks)
4. a. What is an operon? b. How do inducible operons (e.g., the lactose operon) and repressible operons (e.g., the tryptophan operon) benefit a bacterial cell? (5 marks)
5. Explain the possible role of telomerase in cellular aging and in cancer formation. (6 marks)
6. a. Draw a diagram to show what could happen during meiosis that would result in an egg with two X chromosomes. b. If this egg is fertilized and develops, what are the possible karyotypes of the offspring? (6 marks)
7. A female yellow Labrador retriever homozygous for coat colour (bbee) is mated with a male black lab. They have two chocolate puppies, three black puppies and one yellow puppy. What is the genotype of the father? Use Punnett squares to show your reasoning. (2 marks)
8. What is a proteome, and why is it studied in addition to (or instead of) the genome?
Explanation / Answer
Que 1.
Ans:
CDKs regulate cell division:
- Cyclin dependent kinases (CDKs) are protein kinases chracterized by needing a seperate subunit - a cyclin- that provides domains essential for enzymatic activity.
- CDKs play important roles in the control of cell division. CDKs are kinases, enzymes that phosphorylate specific target proteins. The attached phosphate group acts like a switch, making the target protein less or more active.
- When cyclin attaches to a CDK, it has a two important effects: it activates the CDK as a kinase, but it also directs the CDK to a specific set of target proteins, once appropriate to the cell cycle peroid controlled by the cyclin.
- For instance, G1/S cyclins send CDKs to S phase targets (e.g. promoting DNA replication), while M cyclins send CDKs to M phase targets ( e.g. making the nuclear membrane break down).
- In general CDKs level remain relatively constant across the cell cycle, but CDK activity and target proteins change as the level of various cyclins rise and fall.
- A CDKs is an enzyme that adds negatively chrged phosphate group to other molecules in process called phosphorylation.
- Through phosphorylation, CDKs signal the cell that it is ready to pass into the next stage of the cell cycle.
- Cyclins bind to CDKs to form cyclin-CDK complex. Eventually, the cyclin degrades, deactivating the CDK, thus signalling exit from particular phase.