Transcription

Question 1

How many different types of RNA polymerase are there in bacteria?

Answer 1

1

Question 2

What are three differences between DNA and RNA polymerases?

Answer 2

1. RNA pol doesn’t need primers.
2. RNA pol uses NTPs (not dNTPs).
3. RNA pol uses shorter stretches of DNA.

Question 3

What are the two main ‘subunits’ of bacterial RNA polymerase?

Answer 3

1. Core tetramer.
2. Sigma subunit.

Question 4

What is the role of the sigma subunit in bacterial RNA pol?

Answer 4

Transcription initiation.

Question 5

The template strand is the coding strand. True or false?

Answer 5

False.

Question 6

The sense strand is transcribed by RNA polymerase. True or false?

Answer 6

False.

Question 7

What is the first step of transcription?

Answer 7

Binding of RNA polymerase to the promoter.

Question 8

Are E. coli promoters upstream or downstream of the start site?

Answer 8

Upstream.

Question 9

What are the two main motif regions that help direct RNA pol in bacterial promoters?

Answer 9

-35 and -10 regions.

Question 10

When does the sigma subunit of bacterial RNA polymerase disassociate in the transcription process?

Answer 10

After its corresponding promoter is found and the core enzyme binds.

Question 11

RNA polymerase does not require helicase. True or false?

Answer 11

True.

Question 12

How large is the transcription bubble?

Answer 12

17 bp.

Question 13

In E. coli genes, what is the general termination signal? Why?

Answer 13

Inverted, GC-rich sequence. Creates stem-loop structure due to self-complementarity.

Question 14

In eukaryotes, what RNA pol in the nucleoli synthesises rRNA precursors?

Answer 14

RNA pol I.

Question 15

In eukaryotes, what RNA pol in the nucleoplasm synthesises mRNA precursors?

Answer 15

RNA pol II.

Question 16

In eukaryotes, what RNA pol in the nucleoplasm synthesises tRNAs?

Answer 16

RNA pol III.

Question 17

What replaces sigma subunit function in eukaryotes?

Answer 17

Transcription factors.

Question 18

What are three differences comparing bacterial to eukaryotic transcription?

Answer 18

1. Bacterial transcription/translation can be simultaneous.
2. Eukaryotes don’t have sigma subunits.
3. Eukaryotes have several RNA polymerases (including organelle-specific).

Question 19

What is a ‘constitutively’ expressed gene?

Answer 19

The gene is transcribed in all tissues.

Question 20

What core promoter element in eukaryotes resembles the bacterial -10 region?

Answer 20

TATA box.

Question 21

What promoter element in eukaryotes is around -70 and -90?

Answer 21

CCAAT box.

Question 22

What class of regulatory element increases transcription rate?

Answer 22

Enhancers.

Question 23

What class of regulatory element decreases transcription rate?

Answer 23

Silencers

Question 24

Target sequences for signalling molecules are also called…

Answer 24

Response elements.

Question 25

What are the three main post-transcriptional mRNA modifications?

Answer 25

1. 5’ capping
2. 3’ polyadenylation
3. Splicing events.

Question 26

Do rRNAs and tRNAs undergo post-transcriptional modification?

Answer 26

Yes.

Question 27

What is a central reason post-transcriptional modification is necessary in eukaryotes?

Answer 27

Eukaryotes don’t have transcription termination sites.

Question 28

What is added to the 5’-end of eukaryotic mRNA as a ‘cap’?

Answer 28

7-methylguanosine.

Question 29

What are two functions of the 5’ cap?

Answer 29

1. Identify the translation start site.
2. Protect from 5’ exonucleases.

Question 30

What is the weird connection between the 5’ cap and the transcript called?

Answer 30

5’-5’ triphosphate bridge.

Question 31

What is the ~250 nucleotide addition to the 3’ end of eukaryotic mRNA transcripts called?

Answer 31

Poly(A) tail.

Question 32

What are the two functions of the 3’ tail?

Answer 32

1. Acts as a handle for ribosomal delivery.
2. Protect from 3’ exonucleases.

Question 33

What enzyme generates the poly(A) tail?

Answer 33

Poly(A) polymerase.

Question 34

Why can eukaryotes but not bacteria have splicing events?

Answer 34

Bacteria don’t have unexpressed regions.

Question 35

What are two other terms for primary mRNA transcripts?

Answer 35

1. Pre-mRNAs.
2. Heterogeneous nuclear RNAs (hnRNAs).

Question 36

What complex carries out splicing?

Answer 36

The spliceosome.

Question 37

What post-transcriptional modification can lead to different protein expression from the same gene?

Answer 37

Alternative splicing.

Question 38

What is spliced together in splicing - introns or exons?

Answer 38

Exons.