Gene Expression

Question 1

DNA properties

Answer 1

antiparallel double-stranded helix
ATGC
less reactive - 2’ deoxyribose

Question 2

RNA properties

Answer 2

single-stranded
AUGC
more reactive - 2’ OH in ribose

Question 3

Types of RNA

Answer 3

1. ribosomal (rRNA) 2/3 of ribosomes
2. transfer (tRNA) molecules that deliver amino acids to ribosomes
3. messenger (mRNA) nucleotide sequences that direct protein synthesis

Question 4

How do all cellular RNAs arise?

Answer 4

transcription from DNA templates, using DNA-dependent RNA polymerases, which are directed to specific genes (unlike DNAPs)

Question 5

Action of RNA Polymerase

Answer 5

couples ribonucleotide triphosphates on DNA template (eg. ATP) which is driven by the release and hydrolysis of PPi

Question 6

Is a primer needed in prokaryotic transcription?

Answer 6

no and template is fully conserved

Question 7

How is porkaryotic transcription intiated?

Answer 7

promoters - RNAP binds to initiation site through base sequences (promoter), which is recognised by RNAP sigma factor
lies upstream of RNA’s starting nucleotide

Question 8

What causes the DNA strands to separate?

Answer 8

RNAP holoenzyme binds in its vicinity

Question 9

What direction is RNA synthesis?

Answer 9

5’ to 3’

Question 10

What kind of genome is produced from RNA synthesis in PT?

Answer 10

small, single strand genome portions

Question 11

Is PT rapid?

Answer 11

yes - RNA synthesis initiated as soon as RNAP clears promoters
and protein synthesis can begin before RNA is completely synthesised (only in Ps)
RNAP is processive and does not dissociate from DNA template

Question 12

How is transcription terminated in prokaryotes?

Answer 12

DNA contains specific termination sites:
1. series of 4-10 AT bases
2. A,G,C rich region with palindromic sequence
RNA transcript form self-complementary hairpin, causing RNAP to pause and changes it conformationally

Question 13

How do some prokaryotes terminate transcription without the intrinsic terminator?

Answer 13

‘Rho factor’ - helicase that runs along RNA until caused RNAP is found. Pushes it, causing rewinding of dsDNA and release of RNA

Question 14

How does ET differ to PT?

Answer 14

similar, but have multiple RNAPs, therefore more complicated control sequences
RNAPs have greater subunit complexity
RNAPs do not have sigma factor
Enhancers

Question 15

What is used to identify promoters in ET?

Answer 15

accesory proteins which ID promotors and recruit the RNAPs

Question 16

What are enhancers?

Answer 16

certain sequences that encourage transcription

recognised by TFs and can stimulate RNAP II binding and mediate selective gene expression (in Es)

Question 17

What are general transcription factors?

Uses?

Answer 17

equivalent of sigma factor

1. needed for RNAP II transcription
2. permit basal expression
3. targeted to TATA box by TBP
4. switching transcription machinery to elongation mode after RNAP II initiates RNA synthesis

Question 18

What is the preinitiation complex?

Answer 18

in basal expression, where TFs combine with an enzyme and DNA

Question 19

How can transcription be inhibited?

Answer 19

antibiotics which target RNAP’s essential functions

Question 20

What is RNA capping?

Answer 20

RNAp contains CTD, which, when phosphorylated, recruits capping enzyme complex. This modifies the 5’ end to a 7-methylguanosine (joined by 5’-5’-triphosphate bridge)
involves several enzymatic reactions

Question 21

Use of RNA capping

Answer 21

provides resistane to degradation and ID of translation start site

Question 22

What is polyadenylation?

Answer 22

part of transcription termination, part of the process for producing mRNA for translation
poly(A) added to mRNA
poly (A) tail protects the mRNA from degradation, aids in the export of the mature mRNA to the cytoplasm

Question 23

Splicing

Answer 23

introns removed

splicesomes carry out

Question 24

Why are introns removed?

Answer 24

source of vulnerability

not required to make polypeptide

Question 25

What are spliceosomes?

Answer 25

small ribonucleoproteins (snRNAs + proteins)

Question 26

What is alternative splicing?

Answer 26

where primary transcripts are spliced in different ways

leads to proteins with differing destinations in the cell with different catalytic/interactive properties