Neyfakh-Questions (77 points)

 

1. 18 points. Approximately 99% of human DNA does not code for proteins. Which of the following statements about this “junk” DNA are true (mark them with T) and which are false (mark them with F)?

 

A) Part of this junk DNA is located within protein-coding genes.   T

 

B) Part of this junk DNA are plasmids integrated into the genome.  F

 

C) Part of this junk DNA are DNA copies of RNA, which were generated by reverse   T transcriptase.

 

D) Part of this junk DNA contains uridine instead of thymidine.   F

 

E) Part of this junk DNA is the same nucleotide sequence repeated thousands times. T

 

F) Part of this junk DNA is transcribed.  T

 

2. 10 points. Which of the following viruses must carry a polymerase (either DNA-polymerase, or reverse transcriptase, or RNA replicase) in viral particles. Mark T the ones which do, and F the ones which do not.

 

A) Viruses whose genome is ssDNA.   F

 

B) Retroviruses. T

 

C) Viruses whose genome is dsRNA. T

 

D) Viruses whose genome is (+) ssRNA. F

 

E) Viruses whose genome is (-) ssRNA. T

 

3. (14 points) A plasmid vector containing the gene for the cro protein of bacteriophage lambda has been constructed. In this vector, the cro gene is placed under control of the regulatory region of the lac operon.  The E. coli cells containing this vector were infected with bacteriophage lambda. Will anything happen to these cells upon the addition of lactose to the medium. Explain (do not exceed the space below).

 

Lactose will induce expression of the cro protein. Cro protein will shut down cI expression from the bacteriophage genome and induce expression of other bacteriophage genes, which will eventually lead to the formation of phage particles and cell lysis.

 

 

 

 

 

4. (15 points) What level of expression of the Lac operon (high, low, or none) would you expect in the following strains of E. coli placed into a medium containing no glucose and no lactose:

 

a) wild-type cells (no mutations)      None

 

 

b) cells with destroyed gene of Lac repressor   High

 

 

c) cells with highly mutated operator region    High

 

 

d)cells with destroyed genes of CRP and Lac repressor   Low

 

 

e) cells with destroyed genes of adenylate cyclase (an enzyme which makes cAMP) and Lac repressor      Low

 

 

 

5. (10 points; no answer - 3 points) Tumors arise because of the activation of oncogenes or mutations in antioncogenes. Many retroviruses contain an oncogene in their genome. Why does not any of them contain a mutated antioncogene? Do not exceed the space provided.

 

Mutations in antioncogenes are genetically recessive. A mutated copy of the antioncogene, brought by a virus, will not manifest itself because each cell contains two copies of an intact antioncogene.

 

 

 

 

6. (10 points) There are many cells in the organism which are dividing faster than tumor cells. Why does antitumor therapy work? Indicate whether the following answers are true (T) or false (F).

 

A) Because antitumor drugs interact specifically with the products of oncogenes.  F

 

B) Because antitumor drugs eliminate stem cells.   F

 

C) Because the population of normal cells is replenished from stem cells.    T

 

D) Because the population of tumor cells has more active apoptosis system.   F

 

E) Because antitumor drugs activate anti-tumor immune response.   F