Questions 5 and 6 deal with the prokaryotic promoter sequence shown below 5’-ATC

Question

Questions 5 and 6 deal with the prokaryotic promoter sequence shown below

5’-ATCGGTACCGTTGACAATCGACTAGGCTAGCTTATATTGTACGTAGGTC-3’

3’-TAGCCATGGCAACTGTTAGCTGATCCGATCGAATATAACATGCATCCAG-5’

5. The bold sequences (TTGACA and TATATT) represent

a. TATA boxes recognized by RNAP II

b. -35 and -10 boxes recognized by the sigma factor of RNAP

c. Binding sites for general transcription factors

d. Binding sites for the small subunit of the ribosome

6. If transcription starts at the arrow, the sequence of the transcribed RNA will be:

a. 5’-AGGTC…-3’

b. 5’-AGGUC…-3’

c. 5‘-TCCAG…-3’

d. 5’-UCCAG…-3

7. You have identified a protein factor that when added to in vitro protein synthesis reaction increases the incorporation of 35S-methionine from 4 pmoles/minute to 8 pmoles/min. When you centrifuge these reactions and measure polyribosomes and free ribosomes, you observe that more of the ribosomes are present as polyribosomes for the reactions that contain your stimulatory factor. Which explanation is consistent with this result?

a. Your factor binds to the small subunit to promote translation initiation

b. Your factor binds to the large subunit to promote translation termination

c. Your factor binds to the ribosome to decrease the rate of elongation

d. Your factor binds to the ribosome to increase the rate of elongation

10. The concentration of a particular protein X in a normal human cell rises gradually from a low point, immediately after cell division, to a high point, just before cell division, and then drops sharply. The level of its mRNA in the cell remains fairly constant throughout this time. Protein X is required for cell growth and survival, but the drop in its level just before cell division is essential for division to proceed. You have isolated a line of human cells that grow in size in culture but cannot divide, and on analyzing these mutants, you find that levels of X protein do not decrease. Which of the following mutations could explain these results?

a. A mutation that results in the loss of an enzyme that adds a ubiquitin tag to the protein.

b. a mutation in gene X that results in the loss of polyA addition to its mRNA

c. a mutation in gene X that changes the sequence that encodes sites at which ubiquitin can be attached to the protein

d. Both A and C

Explanation / Answer

5. Option b

TTGACA : -35 region

TATAAT : -10 region

Negative sign denotes upstream region of transcription initiation site.

6. Option a

The start site of transcription is N6 or N7 away from -10 region.

7. Option a.

Methionine is the start codon of transcription. 35s- methionine is a labelled amino acid. When we observe many methionine, it means the transcription initiation is enhanced.

8. Option c

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