Gene expression

Question 1

The production if RNA from DNA is carried out by

Answer 1

DNA-dependant RNA polymerases (RNAP)

Question 2

Prokaryotic transcription

Answer 2

Expression involves small single strand genome portions
No primer
And DNA template fully conserved

Question 3

Direction of coding/non-coding strand

Answer 3

Coding strand is 5’ to 3’
Non-coding strand is 3’ to 5’

Question 4

Main difference between prokaryotic and eukaryotic transcription

Answer 4

Genes transcribed individually in eukaryotes
Tandem layout in prokaryotes ; several genes transcribed together (these are called operons)

Question 5

What are promoters?

Answer 5

Base sequences that allow the RNAP to bind and imitate transcription
They are found on the 5’ side, upstream of the starting nucleotide

Question 6

Mutation of the promoter regions can

Answer 6

Regulate transcription

Question 7

What direction does RNA synthesis occur in

Answer 7

5’ to 3’

Question 8

RNAP is processive

explain what this means

Answer 8

RNAP does not dissociate from the DNA template

Question 9

In prokaryotes , protein synthesis can begin before …..

Answer 9

RNA synthesis is completely synthesised

Question 10

Transcription termination

Answer 10

Termination sites contain series of 4-10 AT bases and a G+C rich region with a palindromic sequence

this leads to the RNA formed forming a self complementary hairpin (folds in on itself)

this permits RNAP to make a conformational change that allows termination

Question 11

How many RNAPs involved in prokaryotic/eukaryotic transcription ?

Answer 11

Eukaryotes have multiple RNAPs

prokaryotes have only one RNAP

Eukaryotic RNAPs are larger and have greater subunit complexity

Question 12

Eukaryotic RNAPs

how do they work

Answer 12

Highly complex

can require the action of hundreds of proteins

promoters can be complex and diverse if selectively expressed (to allow specialised function of cells)

Question 13

What are enhancers

Answer 13

Sequences upstream or downstream of the promoter region

they are recognised by TFs which can stimulate RNAP II binding

this allows selective gene expression to occur

they can have a much larger effect on transcription rate than just promoters

Question 14

General transcription factors

Answer 14

Permit basal expression by combining with RNAP and DNA to form a pre-initiation complex

other gene-specific factors needed to further enhance transcription

often targeted to TATA box

different TFs needed once elongation phase begins

Question 15

What is the TATA box

Answer 15

TATA box is a sequence of DNA found in the core promoter region of genes in archaea and eukaryotes

Question 16

What is hnRNA

Answer 16

Pre-mRNA

Question 17

hnRNA processing

Answer 17

Capping → cleavage →polyadenylation → splicing

Question 18

what is RNA capping?

what is the purpose of it?

Answer 18

the 5’ end is modified to a 7-methylguanosine by 5’-5’ triphosphate bridge

this is called a type O cap

involves several different enzymes

provides resistance to degradation and identification of the translation start site

Question 19

Polyadenylation

definition and purpose

Answer 19

Most eukaryotic mRNAs have defined 3’ ends terminating in 250 adenosines

added by poly(A)polymerase and not encoded by sequence

Part of transcription termination

complex formed with poly(A)-binding protein - this prevents degradation

Question 20

What is alternative splicing

Answer 20

Differentials spliced transcripts may lead to proteins with differing catalytic properties

this means 1 gene can encode several different proteins

source of complexity in organism

Question 21

Mutatations in the splice sites of intron sequences can ____

Answer 21

Lead to disease