Transcription

Question 0

Which would you expect to find in an inducible system?

Answer 0

A repressor protein, which is bound to DNA in absence of any other factor.

Question 1

What happens in the lytic cycle of phage replication?

Answer 1

Phage DNA is replicated and transcribed.

Question 2

How does the phage lamba Q protein prevent termination, which allows transcription of the late genes?

Answer 2

Q binds to DNA and then interacts with RNA polymerase.

Question 3

Which best describes the role of the mediator complex in eukaryotic transcription?

Answer 3

Co-activator.

Question 4

When tryptophan is present in the medium, the transcription of tryptophan-producing genes in E. coli is stopped by a helix-turn-helix regulator binding to which structure?

Answer 4

Trp operon.

Question 5

What allows transcription of the lac operon in E. coli in the presence of lactose?

Answer 5

An isomer of lactose binds to the repressor.

Question 6

How do the recognition helices of helix-turn-helix proteins interact with their target DNA?

Answer 6

Both helices bind in the major groove.

Question 7

To what do eukaryotic co-activators and co-repressors bind?

Answer 7

Sequence-specific DNA-binding proteins.

Question 8

Which eukaryotic RNA polymerase transcribes mRNA?

Answer 8

RNA polymerase II

Question 9

Transcription occurs along a _____ template forming an mRNA in the _____ direction.

Answer 9

3’ to 5’; 5’ to 3’

Question 10

What happens each time a nucleotide is added as the transcription bubble passes down the RNA-DNA complex?

Answer 10

Rotation.

Question 11

What is the function of the sigma factor of RNA polymerase?

Answer 11

Assures that transcription begins at the proper point.

Question 12

Not all RNAs produced in the cell encode proteins. Explain.

Answer 12

In some cases, the RNA molecules play a structural role or form part of an enzyme complex. The ribosome is composed mostly of RNA and there are also RNA transcripts that play regulatory roles.

Question 13

Which of the following statements regarding RNA is NOT true?

a. RNA contains the nitrogen base uracil
b. RNA is predominantly double stranded
c. RNA contains the sugar ribose
d. RNA nucleotides are connected by phosphodiester bonds

Answer 13

B

Question 14

What feature of eukaryotic chromosomes presents a barrier to transcription? In general, how do eukaryotic cells overcome this barrier?

Answer 14

The packaging of chromatin. Overcome the chromatin barrier in three ways:

a. nucleosome remodelling enzymes (reproduce histones and histone octamers from one location on the DNA to another
b. histone chaperones (disassemble and reassemble the histone octamer)
c. enzymes that catalyze reversible chemical modification of histone proteins

Question 15

The subunits that make up the core RNA polymerases are capable of synthesizing RNA molecules using a DNA template. Why do they need accessory proteins to function properly?

Answer 15

To target it to promoter sequences.

Question 16

Why is it significant that bacteria, archaea, and eukaryotic RNA polymerases have the highest similarity in the amino acid sequence that contains the active site?

Answer 16

Indicates that all cellular RNA polymerases evolved from a common ancestor.