Transcription (1 & 2)

Question 1

What is transcription?

Answer 1

The copy of information from a DNA sequence (a gene) to a complementary RNA sequence

Question 2

What is translation?

Answer 2

The conversion of an RNA sequence to an amino acid sequence of polypeptides

Question 3

How does RNA differ from DNA?

Answer 3

RNA has one polynucleotide chain with secondary structures (hairpins, loops); the sugar is ribose; bases can pair with a single strand of DNA; can fold into complex shapes by internal base pairing; contains uracil instead of thymine

Question 4

Why does RNA contain uracil and not thymine?

Answer 4

Uracil is energetically less expensive to produce than thymine

Question 5

What direction is RNA synthesised in?

Answer 5

5’ - 3’ direction

Question 6

What are the different types of RNA?

Answer 6

snRNA (spicing of mRNA); tRNA (adaptor between amino acids and mRNA sequences); mRNA (contains protein coding sequence from gene); miRNA (inhibits translation); rRNA (structural and catalytic component of ribosome)

Question 7

What are the components needed for transcription?

Answer 7

a DNA template for base pairings; nucleoside triphosphates (ATP, GTP, CTP, UTP) as substrates; a RNA polymerase enzyme; basic features of a gene

Question 8

What does RNA polymerase catalyse?

Answer 8

Synthesis of RNA

Question 9

Does RNA polymerase need a primer?

Answer 9

No

Question 10

RNA polymerase is recruited by the promoter needed for initiation by what?

Answer 10

Transcription factors that bind to the promoter

Question 11

What happens (in inititation) after the promoter has located RNA polymerase?

Answer 11

RNA polymerase will bind to the promoter and unwind DNA

Question 12

In elongation, what direction does RNA polymerase read the template strand?

Answer 12

3’ - 5’ direction

Question 13

What end does the RNA transcript add nucleotides to the template strand?

Answer 13

The 3’ end

Question 14

Describe what happens in termination?

Answer 14

When RNA polymerase reaches the termination site, the RNA transcript is set free from the template.

Question 15

What are the four subunits of E.coli core RNA polymerase?

Answer 15

2 alpha units and one beta unit and one beta’ unit

Question 16

What is holoenzyme and what does it do?

Answer 16

It is formed by the combination of an enzyme with a coenzyme and cn recognise and bind the promoter

Question 17

What role do sigma factors play in intiation?

Answer 17

They bind consensus sequences in the core promoter

Question 18

What happens to signma factors in elongation?

Answer 18

They are released

Question 19

Are transcripts longer or shorter in elongation?

Answer 19

Longer (because sigma factor are released as they only allow short abortive transcripts to be synthesised)

Question 20

What cause the RNA polymerase to stall in termination?

Answer 20

The form of a hairpin loop from the palindromic sequence

Question 21

What is TFIIB?

Answer 21

It is a general transcription factor that is involved in the formation of the RNA polymerase II preinitiation complex and aids in stimulating transcription initiation

Question 22

What is TFIIE?

Answer 22

It is one of several general transcription factors that make up the RNA polymerase II pre-initiation complex.

Question 23

What is TFIIH?

Answer 23

It is an important protein complex, having roles in transcription of various protein-coding genes and DNA nucleotide excision repair pathway

Question 24

Can TFIIB initiate transcription?

Answer 24

No, even though it has recruited RNA polymerase II?

Question 25

What roles do TFIIE and TFIIH play in transcription?

Answer 25

They stimulate and stabilise promoter opening, to allow for initiation of transcription

Question 26

What does TFIIH trigger?

Answer 26

It triggers promoter escape through the CTD (C-terminal domain) of polymerase II

Question 27

What does the subunit of TFIIH phosphorylated?

Answer 27

The CTD of polymerase II

Question 28

What does the CTF of polymerase couple transcription with?

Answer 28

mRNA processing

Question 29

What processes take place on pre-initiation?

Answer 29

Cleavage; polyadenylation; splicing

Question 30

Describe alternative splicing

Answer 30

It can give more than one product from a single gene and can be regulated to give differential gene expression

Question 31

Are RNA transcripts translated as they are synthesised in prokaryotes or eukaryotes?

Answer 31

Prokaryotes (RNA transcripts must be processed and transported to the cytoplasm before being translated)