Protein Synthesis

Question 1

Describe what happens in transcription

Answer 1

Pre-mRNA
Introns removed
Exons = mRNA

Question 2

What are the major components in translation?

Answer 2

Ribosomes
tRNA
Aminoacyl-tRNA synthetases 
mRNA molecules
Protein factors (facilitators)

Question 3

What are the sites found in ribosomes?

Answer 3

E-site = exit (where tRNA leaves)
P-site = peptidyl (where peptides grow)
A-site = amino acyl (where incoming amino acids enter)

Question 4

What do prokaryotes have?

Answer 4

70s ribosomes

= 30s subunit + 50s subunit

Question 5

What do eukaryotes have?

Answer 5

80s ribosomes

= 40s subunit + 60s subunit

Question 6

Describe initiation

Translation

Answer 6

tRNA binds to small ribosomal unit
Complex scans to find start codon
Initiator tRNA binds to start codon
Large ribosomal subunit joins to form initiation complex

Question 7

How many codons is there?

Answer 7

64

Question 8

How many amino acids is there?

Answer 8

20

Question 9

Describe elongation

Translation

Answer 9

mRNA shifted forward, exposing new codon
tRNA binds to matching codon
Polypeptide is linked to new amino acid

Question 10

Describe secondary structure of tRNA

Answer 10

Amino acid attachment site
Anti-codon
Clover leaf structure
Base pairing

Question 11

Describe tertiary tRNA structure

Answer 11

L shaped tRNA
Single conformation of tRNA increases efficiency of binding within ribosome
Amino acid in correct position for formation of peptide bonds

Question 12

How is aminoacyl-tRNA formed?

Answer 12

ATP + amino acid —-> aminoacyl-AMP —-> aminoacyl-tRNA

Question 13

What does aminoacyl-tRNA do?

Answer 13

Allows tRNA to pick up amino acid using ATP

Question 14

Describe termination

Translation

Answer 14

Ribosome reaches stop codon on MRNA
The A site of ribosome accepts protein called release factor instead of tRNA
Hydrolyses bod between tRNA + P site + last amino acid of polypeptide
2 ribosomal subunits + other components of assembly dissociate

Question 15

Describe GM insulin

Answer 15

Bacteria with plasmid

Insert gene that makes insulin into it

Question 16

What are the post-translational modification of proteins?

Answer 16

Proteolysis
Glycosylation
Phosphorylation

Question 17

What is proteolysis?

Answer 17

Polypeptide chain is cleaved into fragments which takes on different shapes

Question 18

What is glycosylation?

Answer 18

The addition of sugars to polypeptide chains

Important in targeting + recognition

Question 19

What is phosphorylation?

Answer 19

The addition of phosphate groups

Often changes the shape of protein, exposing an active site of an enzyme or binding site for another molecule

Question 20

What happens in post-translational modification of proteins?

Answer 20

Leader sequence aids transfer of polypeptide over membrane
After transfer leader sequence removed by cleavage
Proinsulin folds into favourable conformation
Disulphide bonds form
Connective sequence cleaved + active form of insulin observed