Lecture 7 - Transcription 1

Question 1

Transcription

Answer 1

Copies information from a DNA sequence (a gene) to a complementary RNA sequence

Question 2

Translation

Answer 2

Converts RNA sequence to amino acid sequence of a polypeptide

Question 3

Ways in which RNA differs from DNA

Answer 3

1. Usually one polynucleotide strand (with secondary structures; hairpins, loops)
2. The sugar is ribose
3. Bases in RNA can pair with a single strand of DNA (A-U)
4. Single-strand RNA can fold into complex shapes by internal base pairing
5. Contains Uracil instead of Thymine

Question 4

Why is there Thymine and not Uracil in DNA?

Answer 4

Because Cytosine can be deaminated which converts it into Uracil, the cell can tell when that is an error and uracil DNA glycosylase comes and puts in a cytosine again. If Uracil was a base this important pathway wouldn’t work as there would be no way to tell if it was incorporated normally or a deamination error

Question 5

In which direction is RNA synthesized?

Answer 5

5’ to 3’ direction

Question 6

5 types of RNA

Answer 6

1. snRNA
2. tRNA
3. mRNA
4. rRNA
5. miRNA

Question 7

snRNA

Answer 7

Required for splicing of mRNA

Question 8

tRNA

Answer 8

Adaptor between amino acids and mRNA sequence

Question 9

miRNA

Answer 9

Inhibits translation

Question 10

mRNA

Answer 10

Contains protein coding sequence from gene

Question 11

rRNA

Answer 11

Structural and catalytic component of ribosome

Question 12

Promoter

Answer 12

Determines where to start and which direction to transcribe. (Not all promoters are identical)

Question 13

RNA polymerase

Answer 13

• Catalyzes synthesis of RNA

- Do not need primers unlike DNA polymerases

Question 14

Transcription factors

Answer 14

RNA polymerase is recruited to the promoter by transcription factors that recognize and bing the promoter

Question 15

Initiation

Answer 15

1. Binding of RNA polymerase to double-stranded DNA at the promoter
2. Transition to single-strandedness in the region of binding

Question 16

Elongation

Answer 16

1. RNA Polymerase released the sigma factor
2. Elongation factors bind and transcription proceeds
3. RNA polymerase unwinds DNA about 10bp at a time
4. Adds nucleotides to the 3’ of the RNA transcript

Question 17

Termination

Answer 17

1. Recognition of transcription termination DNA sequence (many function by forming an RNA hairpin-like structure that destabilizes the polymerases’s hold on the RNA)
2. Release of RNA polymerase
3. U-rich stretch downstream of termination signal allows transcript to fall off the template

Question 18

Consensus sequence

Answer 18

A sequence of DNA having similar structure and function in different organisms

Question 19

RNA polymerase holoenzyme

Answer 19

Associated sigma factor and RNA polymerase core enzymes

Question 20

How does promoter binding work?

Answer 20

• Normally RNA polymerase holoenzyme adheres weakly to bacterial DNA when they collide
• However if the polymerase holoenzyme slides into a special sequence of nucleotides, the promoter, it binds tightly because the sigma factor makes specific contacts with the edges of bases exposed on the outside of the DNA double helix.

Question 21

What transcripts are synthesized while sigma factor remain bound?

Answer 21

Only short (abortive) transcripts can be synthesized whilst sigma factor remains bound to the promoter