MCBG gene expression. topic 13

Question 1

which is the 5’ and 3’ end of tRNA?

Answer 1

5’-left. shorter.
3’ right
(see photo google)

Question 2

to which end of tRNA molecule is an amino acid attached?

Answer 2

the 3’ OH

amino acid attachment site

Question 3

which enzyme catalyses the charging of a tRNA molecule with its cognate activated amino acid

Answer 3

amino acyl tRNA synthetase

Question 4

what is the role of amino acyl tRNA synthetase? describe process

Answer 4

Charging of tRNA

1) amino acid and ATP bind to enzyme
2) amino acid is coupled to AMP forming aminoacyl-AMP. two phosphates lost.
3) uncharged tRNA binds to enzyme
4) amino acid transferred from aa-AMP to tRNA to form aminoacyl tRNA (charged tRNA)

> products released. enzyme returns to original state.

Question 5

which bases can purine nucleoside inosine (I) complementary bind to?

Answer 5

A/C/U

Question 6

what is the difference between nucleotide and nucleoside

Answer 6

nucleotide- phosphate, sugar, base

nucleoSIDE- sugar AND base (NO phosphate)

Question 7

which bases are purine which are pyrimidine?

Answer 7

purine-
Adenine
Guanine

(All Girls are pure)

pyrimidine-
Thymine/ Uracil
Cytosine
(all contain a Y)

Question 8

key feature about tRNA anticodon

anticodon= 5’ UAC 3’ codon=?

Answer 8

recognises ANTIPARALLEL complementary codon

codon= 3’ AUG 5’

Question 9

compare and contrast DNA to RNA

Answer 9

• RNA has ribose sugar (C2 OH group)
• RNA contains U instead of T
• RNA single stranded
• RNA forms stem loops ( complementary, antiparallel strands which form mini helix)
• RNA can form non standard base pairing, complex 3D structure (e.g. 3 linked base pairs)

Question 10

describe the relative amount of each type of RNA and the amount of different kinds and copies of each

Answer 10

rRNA

• most abundant
• few kinds, many copies

tRNA

• 15% of total RNA
• 100 kinds, many copies

mRNA

• least abundant
• 1000s of kinds, few copies

Question 11

what does a gene contain

Answer 11

coding region

AND regulatory sequences around it (promoter, transcription initiation/ terminator, transcription termination)

Question 12

where is the promoter in relation to transcription initiation?

Answer 12

promoter is UPSTREAM

Question 13

what are the other minor types of RNA

Answer 13

• non coding RNA
• snRNA > splicing
• miRNA > regulation of gene expression
• antisense RNA > complimentary copy of mRNA

Question 14

role of transcription factor

Answer 14

TF binds promoter
binding is directional on the TATA box (specific sequence on all eukaryotic promoter sequences)
more TF bind to upstream sequences
RNA polymerase recruited (beginning initiation)

Question 15

for transcription elongation which strand is coding and which is non coding?

Answer 15

non transcribed DNA= coding strand

transcribed DNA = non-coding strand (template)

Question 16

what is the role of capping?

Answer 16

5’ cap. put on 5’ to 5’ phosphodiester bond

• provides protection
• role in translation

Question 17

role of tailing? enzyme involved?

Answer 17

3’ polyA tail

• protection
• regulation

endonuclease

Question 18

splicing carried out by?

Answer 18

spliceosomes

Question 19

what are the 3 sites on the large ribosomal subunit

Answer 19

5’ EPA 3’

only two sites occupied at one time

Question 20

which enzyme catalyses the peptide bond formation in translation elongation

Answer 20

peptidyltransferase

Question 21

Describe translation initiation in detail

Answer 21

1) met cap is recognised by tRNA* met
> finds AUG start codon
2) initiation factors removed
3) large ribosomal subunit recruited producing functional ribosome complex

E
P site- contains tRNA met bound to AUG
A- free ready for elongation

Question 22

describe translation elongation in detail

Answer 22

1) P site already occupied. binding of aminoacyl-tRNA on A site
2) peptide bond formation between 2 amino acids
3) peptidyl tRNA moves to P site (translocation), freeing up A site
> pushes the now uncharged tRNA to E site

Question 23

describe translation termination in detail

Answer 23

1) P site contains peptidyl-tRNA. empty A site.
2) stop codon recognised by release factor causing hydrolysis reaction resulting in uncharged tRNA in P site and free peptide
> peptide leaves ribosome through exit tunnel in large ribosomal subunit
3) dissociation of ribosome into subunits

Question 24

compare prokaryote and eukaryote ribosomes

Answer 24

prokaryote- 30s and 50s subunits
70s

eukaryote - 40s and 60s subunits
80s

Question 25

describe features of RNA polymerase in prokaryotes

Answer 25

RNAP CORE enzyme- has 5 subunits
HOLOenzyme - has 6 subunits (core enzyme + sigma)

non specific DNA binding by core enzyme
sigma subunit needed to make specific RNA

Question 26

what additional molecules required for translation

Answer 26

initiation factors
elongation factors
release factors
energy GTP/ATP