Gene expression Flashcards

1
Q

The production if RNA from DNA is carried out by

A

DNA-dependant RNA polymerases (RNAP)

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2
Q

Prokaryotic transcription

A

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

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3
Q

Direction of coding/non-coding strand

A

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

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4
Q

Main difference between prokaryotic and eukaryotic transcription

A

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

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5
Q

What are promoters?

A

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

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6
Q

Mutation of the promoter regions can

A

Regulate transcription

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7
Q

What direction does RNA synthesis occur in

A

5’ to 3’

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8
Q

RNAP is processive

explain what this means

A

RNAP does not dissociate from the DNA template

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9
Q

In prokaryotes , protein synthesis can begin before …..

A

RNA synthesis is completely synthesised

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10
Q

Transcription termination

A

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

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11
Q

How many RNAPs involved in prokaryotic/eukaryotic transcription ?

A

Eukaryotes have multiple RNAPs

prokaryotes have only one RNAP

Eukaryotic RNAPs are larger and have greater subunit complexity

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12
Q

Eukaryotic RNAPs

how do they work

A

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)

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13
Q

What are enhancers

A

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

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14
Q

General transcription factors

A

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

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15
Q

What is the TATA box

A

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

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16
Q

What is hnRNA

A

Pre-mRNA

17
Q

hnRNA processing

A

Capping → cleavage →polyadenylation → splicing

18
Q

what is RNA capping?

what is the purpose of it?

A

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

19
Q

Polyadenylation

definition and purpose

A

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

20
Q

What is alternative splicing

A

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

21
Q

Mutatations in the splice sites of intron sequences can ____

A

Lead to disease