Protein Synthesis

Question 1

Translation

Answer 1

RNA to protein

occurs at ribosomes

Question 2

Ribosomes structure

Answer 2

large, bind to mRNA to read codons

binding sites for tRNA molecules

Question 3

Ribosomes function

Answer 3

mediate interaction of non-ribosomal protein factors to promote: polypeptide chain initiation, elongation and termination
catalyse peptide bond formation
capable of movement, allow translation of codons

Question 4

Prokaryotic ribosomes

Answer 4

70S
2 subunits: small - 30S, large - 50S
ribosomal proteins located on subunit back and sides, not near tRNA and mRNA binding sites

Question 5

tRNA binding sites

Answer 5

A site: aminoacyl, tRNA and amino acid first loaded here
P site: peptidyl, elongating p chain present and linked to
tRNA
E site: exit site, tRNA stripped of polypeptide chain

Question 6

Eukaryotic ribosomes

Answer 6

80S
small subunit: 40S
large: 60S
more complex

Question 7

tRNA binding

Answer 7

all 3 tRNAs have anticodons which bind to 30S subunit, rest bind to 50S
tRNAs on A site and P site interact with mRNA via base pairings

Question 8

Trnaslation requirements

Answer 8

factors for peptide synthesis (catalytic, stabilisers)

ATP, GTP

Question 9

WHat direction is mRNA read in translation

Answer 9

5’ to 3’
protein made N’ to C’ terminal
mRNA synthesised this way

Question 10

Describe chain elongation

Answer 10

linking growing polypeptide to incoming tRNA’s amino acid residue

1. transferred from peptidyl-RNA at the P to A site
2. new peptidyl-tRNA transferred from A to P site
3. unchanged tRNA moves to E site

Question 11

Difference between eukaryotic and prokaryotic mRNA

Answer 11

p: can have more than one coding region (polycistronic)
e: just one coding region (monocistronic)

Question 12

Translation phases

Answer 12

initiation
elongation
termination

Question 13

Initiation

Answer 13

assembly of translationsystem components
initiation tRNA does not bind in A site, binds at P site instead
recognises start codon (AUG) via Shine-Dalgorno sequence - ps
es: 40S ribosomal subunit structure binds to cap structure

Question 14

Elongation

Answer 14

addition of AAs to carboxyl end of pp chain
delivery to tRNA by elongation factorss, requires GTP hydrolysis
translocation, ribosome moves 3 nucleotides to mRNA 3’ end
movement of uncharged tRNA from P to E
peptidyl-RNA from A to P

Question 15

Termination

Answer 15

recognised by release factors (RF-1, RF-2)
RF binding: hydrolysis of peptide bond to tRNA P site, protein released
release of RF1 and 2, GTP hydrolysed

Question 16

Protein synthesis inhibitors

Answer 16

antibiotics which block translation
eg. streptomycin - low conc: ribosome misreads
high conc: prevents initiation
chloramphenicol
tetracycline

Question 17

Co- and posttranslational modification

Answer 17

co: still attached to ribosome
covalently attached functional groups (eg. phosphates by kinases)
remove N-terminal Met or fMet for signal recognition
carb group added: to be secreted or for cell membrane