Gene Expression 1 - Transcription

Question 1

Transcription

Answer 1

Makes messenger RNA copy of the information in a gene that codes for protein

Question 2

Translation

Answer 2

Conversion of RNA message into protein at ribosome

Question 3

What is the additional step of transcription in eukaryotes

Answer 3

• RNA processing
• RNA transport

Question 4

What is a gene composed of

Answer 4

Specific base sequences organised in a way that allows DNA to be transcribed

Question 5

What do genes contain that are NB for transcription

Answer 5

• Promoter
• Terminator
• Other regulatory sequences

Question 6

Position of the promoters

Answer 6

• -10 (Pribnow box) & -35 bases before transcription start site
• (in the region preceding transcription and 10 nucleotides back)

Question 7

Which enzyme catalyses transcription

Answer 7

RNA polymerase

Question 8

What do the two alpha subunits of RNA polymerase do

Answer 8

The two alpha subunits assemble the enzyme & bind regulatory factors

Question 9

What does the beta subunit of RNA polymerase do

Answer 9

Beta subunit has the polymerase activity (catalyses synthesis of RNA), which includes chain initiation & elongation

Question 10

What does the omega subunit of RNA polymerase do

Answer 10

Restores denatured RNA polymerase to its functional form in vitro. Promotes enzyme assembly.

Question 11

What does the sigma subunit of RNA polymerase holoenzyme do

Answer 11

1.Reduces affinity of enzyme for non specific DNA
2.Increases affinity for promoter sites

Provides specificity of enzyme by directing enzyme to appropriate transcription start sites.

Question 12

When does the sigma factor dissociate from core enzyme

Answer 12

Once a promoter has been bound and first few nucleotides have been bound together

Question 13

How is the initiation of transcription in eukaryotes more complex

Answer 13

• RNA polymerase does not directly recognize the core promoter sequences.
• Transcription factors mediate binding of RNA polyermase forming a transcription initiation complex.

Question 14

What does RNA polymerase do during elongation

Answer 14

• Polymerase unwinds DNA ahead of it & rewinds DNA behind it
• This maintains an unwound region of about 17 base pairs in region of transcription

Question 15

How is the template strand of DNA copied to RNA

Answer 15

Using complementary base pairing & insertion of appropriate ribonucleotides

Question 16

Can RNA polymerase proofread??

Answer 16

YESSS

Question 17

Can multiple RNA polymerases transcribe a single DNA molecule at the same time

Answer 17

YESS OFC

Question 18

How does termination of transcription occur in prokaryotes

Answer 18

Rho dependent or Rho independent process - both lead to release of mRNA transcript

Question 19

How does termination of transcription occur in eukaryotes

Answer 19

• LEss understood
• Occurs in conjunction with polyadenylation of the transcripts

Question 20

Steps of Rho dependent termination

Answer 20

1. Rho protein binds to single stranded RNA as it exits from polymerase enzyme complex
2. Moves along the mRNA strand
3. Uses a helicase activity to release the mRNA from enzyme complex

Question 21

How does Rho independent termination occur

Answer 21

Termination due to specific sequence in terminator DNA

Question 22

In what direction does addition of nucleotides occur in template strand (by RNA polymerase)

Answer 22

Nucleotides added in the 5’ to 3’ direction by RNA polymerase

Question 23

Directionality of template strand

Answer 23

3’ to 5’

Question 24

In what direction does the coding DNA strand run in

Answer 24

Runs in the 5’ to 3’ direction

Question 25

What does the coding DNA strand contain that is the same in the mRNA strand

Answer 25

The same nucleotide sequence