6 - Translation

Question 1

Where does translation occur

Answer 1

Cytoplasm

Question 2

How many possible codons

Answer 2

64

Question 3

Start codon

Answer 3

AUG (methionine)

Question 4

3 stop codons

Answer 4

UAA, UAG and UGA

Question 5

Redundancy of the genetic code

Answer 5

a single amino acid may be coded for by more than one codon

Question 6

Unambiguous genetic code

Answer 6

each codon only encodes one amino acid

Question 7

Open reading frame

Answer 7

One of the three possible reading frames that encode a protein

Question 8

tRNA

Answer 8

• An adaptor molecule (30-50 different types).
• Matches amino acids to codons
• Corresponding amino acid attaches to 3’ end of tRNA

Question 9

Anticodon loop

Answer 9

Part of tRNA that base pairs with the amino acid sequence

Question 10

Aminoacyl-tRNA

Answer 10

tRNA with amino acid attached

Question 11

What synthesises aminoacyl-tRNA

Answer 11

Aminoacyl-tRNA synthetase

Question 12

Wobble position

Answer 12

• Not enough tRNAs for each codon so some bind to more than one
• Pairing at 3rd position is relaxed

Question 13

Codon-anticodon pairings allowed by wobble rules

Answer 13

G - C or U
U - A or G
I - U, C, or A

Question 14

What is ribosome made up of

Answer 14

rRNA (2/3) and protein (1/3)

Question 15

2 subunits of ribosome

Answer 15

60S and 40S = 80S ribosome

Question 16

4 RNA components of ribosome

Answer 16

• 18S, 5.8S, and 28S (made from large precursor)
• 5S made from seperate gene

Question 17

4 stages of protein synthesis

Answer 17

1. Amino acid activation (tRNA aminoacylated)
2. Initiation
3. Elongation
4. Termination

Question 18

3 binding pockets of mRNA

Answer 18

• A: Aminoacyl
• P: Peptidyl
• E: Exit

Question 19

initiation of translation

Answer 19

• Met tRNA binds to P site in small subunit
• eIF4g recognises cap on 5’ end of mRNA
• GTP and eIFs required
• Complex slides along mRNA until AUG codon is recognised

Question 20

Elongation of translation

Answer 20

1. tRNA binds to A site
2. Peptide bond formed between tRNA with C terminal amino acid in P site
3. Large subunit moves, leaving two tRNAs in P and E site on large (A and P on small)
4. Small subunit moves (empty tRNA ejected from E site, empty A site)

Question 21

Termination of translation

Answer 21

• Stop codons mark end of translation
• Release factors binds to A site containing stop codon
• Catalyses hydrolysis of last amino acid at P site
• Ribosome complex dissociates

Question 22

Polyribosome

Answer 22

Many ribosomes translating one mRNA molecule simultaneously

Question 23

Nonsense mediated decay

Answer 23

• Many stop codons in introns
• EJCs bond to splice junctions (stripped off when mRNA exists nucleus
• Abnormal splicing leaves extra stop codon
• Up frameshift (Upf) proteins form bridge between upstream stop codons and downstream EJCs
• Ribosome detects Upf complex and triggers mRNA degradation