lecture 17, translation

Question 1

how many codons are there

Answer 1

64

Question 2

how many codons code for amino acids

Answer 2

61

Question 3

what is the start codon on the mRNA/ amino acid

Answer 3

AUG, methionine

Question 4

what are the three stop codons

Answer 4

UAA, UAG and UGA

Question 5

whats the 1st key feature of tRNA that makes it an adaptor molecule

Answer 5

as it is an adaptor it must be able to bond with the mRNA sequence, so there is an amino acid binding site at the three prime end of the tRNA.

Question 6

whats the 2nd key feature of tRNA that makes it an adaptor molecule

Answer 6

the tRNA also needs to interact with the mRNA, so the tRNA has a RNA binding site. This is what we call an anticodon, the complementary 3 nucleotide bases on tRNA to the mRNA codon.

Question 7

what’s the third key feature that makes tRNA an adaptor molecule

Answer 7

tRNA has a structure which is 3d. This 3d structure allows it to fit within the ribosome.

Question 8

what does it mean for the tRNA to be charged

Answer 8

a tRNA that has an amino acid bonded to it

Question 9

how does a tRNA get charged

Answer 9

An enzyme (aminoacyltRNA synthetase),
recognises both a specific
amino acid and the
correct tRNA for this
amino acid and joins
them together

Question 10

what are the three steps in translation

Answer 10

initiation, elongation and termination

Question 11

what’s the first step in the initiation in translation

Answer 11

the tRNA that has the UAC start anticodon, carrying methionine, binds to the small subunit.

Question 12

whats the second step in initiation

Answer 12

2: the small subunit and tRNA then binds to the mRNA at the 5’ g cap

Question 13

whats the third step in initiation

Answer 13

the tRNA and small subunit then move down the mRNA strand until the start codon AUG is reached

Question 14

whats the 4th step in initiation

Answer 14

4: the complex stops and the initator tRNA with methionine is placed in the p site

Question 15

whats the fifth step in initiation

Answer 15

5: the large subunit joins onto the small subunit, making the whole ribosome.

Question 16

first elongation step

Answer 16

A “Charged” tRNA comes onto the mRNA at the codon corresponding to the anticodon on the tRNA.

Question 17

second elongation step, the two things at the same time

Answer 17

2: in this two things occur simultaneously
i) A polypeptide bond gets formed between the amino acid on the A site tRNA and the P site tRNA. The Polypeptide bond between P site tRNA and polypeptide chain is broken, placing the Amino acid chain on the A site tRNA.
ii) The ribosome then moves forward 3 nucleotides placing the A site tRNA in the P site, and the P site tRNA in the E site

Question 18

third elongation step

Answer 18

3: The E site uncharged tRNA is ejected back into cytoplasm where it will be recharged for a future use

Question 19

fourth elongation step in translation

Answer 19

4: the tRNA for the new corresponding codon comes into the A site of the Ribosome and elongation repeats.

Question 20

first termination step

Answer 20

1: when one of the three stop codons is reached a release factor protein binds to mRNA in the A site

Question 21

second termination step

Answer 21

2: This release factor hydrolyses the polypeptide bond between the P site tRNA and the amino acid sequence. Releasing the amino acid chain out of the exit tunnel.

Question 22

third termination step

Answer 22

3: The small and large ribosomal subunits dissociate from the mRNA and each other.

Question 23

what stages of translation require energy

Answer 23

all three of initiation, elongation and termination