TOPIC 2 - GENE EXPRESSION AND TRANSLATION

Question 1

what is transcription

Answer 1

making RNA by using DNA as a template

Question 2

what is the strand called that is read by the RNA polymerase

Answer 2

template strand/ coding strand

Question 3

the coding strand is identical to …

Answer 3

the mRNA synthesised by rna polymerase, differing by U

Question 4

rna polymerase reads the DNA strand

Answer 4

3’ to 5’

and synthesises 5’ to 3’

Question 5

where does energy for rna polymerase to work come from

Answer 5

the breaking of two phosphates while forming a phosphodiester bond

Question 6

what is the transcription bubble

Answer 6

where the 2 strands are unwinded and read in the rna polymerase

Question 7

no. of rna polymerases in prok and euk

Answer 7

prok = 1
euk = 3 (type 1, 2 and 3)

Question 8

outline initiation of transcription

Answer 8

promoter sequence is located 35 & 10bp from start of transcription
sigma factor specific to promoter identifies it and brings rna polymerase to it as a holoenzyme

Question 9

outline intrinsic termination

Answer 9

sequence that forms a hairpin loop after transcription
followed by an unstable sequence of A
polymerase tries to back track to stabilise but can’t because of hairpin
dissociates from mRNA

Question 10

Outline Rho dependent termination

Answer 10

the ‘Rut’ sequence is read by rna poly forming a rho binding site
rho protein attaches and propels down mRNA until it reaches poly
will unwind dna hybrid and cause polymerase dissociation

Question 11

what is translation

Answer 11

the process of producing proteins by using RNA as a template

Question 12

what is a codon

Answer 12

triplet code of nucleotides that corresponds to a specific amino acid

they are read in a 5’ to 3’ direction

Question 13

start and stop codon

Answer 13

start = UAG methionine
stop = UAA, UAG, UGA

Question 14

What is codon degeneracy

Answer 14

refers to how the 3rd nucleotide of the codon can be changed and usually still give the same amino acid

Question 15

what is a reading frame

Answer 15

how the RNA is read to code for amino acids. depends on if the 1st 2nd or 2rd nucleotide is used to start translation

Question 16

outline transfer RNA structure

Answer 16

has an amino acid arm and anticodon arm used to activate

Question 17

outline aminoacyl synthetase

Answer 17

finds the right amino acid to give to the tRNA.

there are only 20 meaning some can bring more than one amino acid

Question 18

where does energy for peptide growth come from

Answer 18

activation of amino acid binding to tRNA

amino acyl-tRNA is formed using ATP which then provides energy for covalent peptide formation

Question 19

what is the wobble hypothesis

Answer 19

some anticodons can tolerate a mismatch at the 3’ position of the codon
this is called the wobble postion
explains why we only need 31 tRNAs instead of one for each codon

Question 20

4 steps of translation

Answer 20

activation of amino acids
initiation
elongation
termination

Question 21

what is a ribozyme

Answer 21

an RNA based enzyme that can catalyse reactions

Question 22

small and large prokaryote ribosomal sub units

Answer 22

30S

50S

Question 23

small and large eukaryote ribosomal sub units

Answer 23

40S

60S

Question 24

Small and large sub units of ribosome functions

Answer 24

small = binding to mRNA, initiation
large = peptide formation (ribozyme activity)

Question 25

outline initiation in prokaryotes

Answer 25

at RBS 16S RNA binds to complimentary "shine delgrano sequence" on mRNA upstream from first codon. first codon lined up with P site IF3 and IF1 block E and A site. IF2 binds to 30s subunit and recruits fMet to correspond to the start codon being read.

Question 26

outline elongation

Answer 26

activated trna enter the ribosome at the A site for corresponding codon peptide chain shifts from trna in p site to a site trna translocation occurs where trnas shift to e and p site. trna in e site is ejected.

Question 27

in elongation the ribosome...

Answer 27

catalyses nucleophilic attack and hydrolyses amino acid from p site to produce new peptide in a site.

Question 28

outline termination of translation

Answer 28

signalled by stop codons codons recognised by release factors factors enter a site causing hydrolysis of last peptide-trna bond and dissociation of the ribosome.

Question 29

outline initiation in eukaryotes

Answer 29

5' cap on mRNA binds to an initiation factor | correct reading frame determined

Question 30

antibiotics that work by blocking translation...

Answer 30

block prokaryotic ribosomes | don't block eukaryotic ribosomes due to the structural difference

Question 31

what is a polyribosome

Answer 31

where multiple ribosomes move along mRNA all at once in eukaryotes: 5' cap binds to initiation factors 4e and 4g allows 3' end to be held close to 5' forms spiral shape producing a polyribosome

Question 32

prokaryotic post translation events

Answer 32

removal of formyl group on fmet | amino acid modifications

Question 33

eukaryotic post translation events

Answer 33

proteolytic maturation complex folding process amino acid modification

Question 34

endoplasmic reticulum translation

Answer 34

translation stalled and finalised as ER surface signal sequence binds to unfinished peptide enters ER through channel signal sequence snipped off and translation resumes feeding into ER other signals cause proteins to move to GA, lysosomes, plasma membrane

Question 35

travelling to become membrane proteins

Answer 35

on way out of cell, get stuck in membrane, embedding them into the organelle making a membrane protein

Question 36

what are chaperones

Answer 36

2 hydrophobic cavities that close with a GroES cap help some 3º structures to form if needed Uses ATP

Question 37

what are proteasomes

Answer 37

proteins are labelled by ubiquitin attachment proteasome recognises the label and degrades the protein to 3-25 aa long uses ATP