Gene expression

Question 1

What is a gene

Answer 1

unit of transcription

Question 2

What is a promoter sequence

Answer 2

TATA box

Question 3

name/ explain the steps involved in the initiation of transcription

Answer 3

promoter recognition
transcription initiation factors bind
RNA polymerase II recruited

Question 4

Name/ explain the steps involved in the elongation of mRNA

Answer 4

DNA strand separated

3’ 5’ strand acts as template so that mRNA produced 5’ to 3’

Question 5

Explain the steps involved in the termination of mRNA production

Answer 5

sequence dependent

specific endonuclease comes and cleaves mRNA a cleavage site

Question 6

What prevents mRNA degradation? How are these added?

Answer 6

5’ cap 5’5 linkage made immediately

polyA tail on 3’ end added by poly A polymerase after termination of mRNA production

Question 7

Why is the DNA sequence often much longer than the mature mRNA?

Answer 7

splicing occurs where introns are removed

Question 8

What ribosomes and their subunits are present in prokaryotes?

Answer 8

30s and 50s

70 s ribosome

Question 9

What ribosomes and their subunits are present in eukaryotes?

Answer 9

40s and 60s

80 s ribosomes

Question 10

What RNA polymerase produces mRNA?

Answer 10

II

Question 11

What RNA polymerase produces tRNA?

Answer 11

III

Question 12

What RNA polymerase produces rRNA?

Answer 12

I

Question 13

Explain the process of translation in simple terms

Answer 13

mRNA read 5’ to 3’
each codon= aa delivered by tRNA
polypeptide produced N–> C

Question 14

Explain the structure of a tRNA molecule

Answer 14

Clover model
tRNA single stranded–> folded to form double stranded regions
H bonds form between antiparallel complementary sequences
bottom= anticodon
3’OH = amino acyl group added

Question 15

How is amino acyl group added to tRNA?

Answer 15

At 3’ OH end
requires ATP and aminoacyl tRNA synthase
pyrophosphate released providing energy to drive reaction

Question 16

What is always the start codon ?

Answer 16

AUG

Question 17

Why is the genetic code described as degenerate?

Answer 17

every 3’ base in codon/ 5’ base in anticodon is in the wobble position meaning it is variable
as a result a single tRNA species recognise more than 1 codon
Degenerate means more than one thing means the same in this instance more than one codon codes for the same amino acid

Question 18

Explain the process of initiation in translation

Answer 18

40s subunit
GTP 
cap binding proteins 
initiation factors 
met-tRNA 
all bind mRNA sequence 
Sequence read 5' to 3' until AUG reached
ATP to ADP energy used to recruit 60s subunit and remove GDP/ initiation factors/ capping proteins
AUG is in ribosome in P site

Question 19

Explain the process of elongation in translation

Answer 19

AUG and met-tRNA in p site, a site empty
aminoacyl tRNA binds at A site GTP –>Pi
Peptide bond forms chain in A site requires enzyme peptidyl transferase
gtp to gdp provides energy for translocation of chain to P site
A site now free for cycle above to repeat

Question 20

What enzyme is required to form peptide bond in translation?

Answer 20

peptidyl transferase

Question 21

How is translation terminated ?

Answer 21

Stop codon reached in A site

water enters ribosome and kicks out protein