Question 20N.2.HL.TZ0.6c
| Date | November 2020 | Marks available | [Maximum mark: 8] | Reference code | 20N.2.HL.TZ0.6c |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Explain | Question number | c | Adapted from | N/A |
Explain how polypeptides are produced by the process of translation.
[8]
a. mRNA is translated;
b. mRNA binds with ribosome/with small subunit of ribosome;
c. tRNA-activating enzymes/aminoacyl tRNA synthetases attach specific amino acid to tRNA;
d. anticodon of 3 bases/nucleotides on tRNA;
e. start codon/AUG on mRNA;
f. tRNA carrying first amino acid/methionine binds to P/peptidyl site (when large subunit binds);
g. anticodon (on tRNA) binds to codon (on mRNA);
h. complementary base pairing (between codon and anticodon);
i. tRNA for next codon binds to A site/amino acyl site;
j. peptide bond forms between amino acids (on tRNAs) at P and A sites;
k. ribosome moves along mRNA to next codon/by three bases/in 5’ to 3’ direction;
l. tRNA released from E/exit site;
m. process/cycle repeats to elongate the polypeptide/until stop codon is reached;
n. release of polypeptide and mRNA/disassembly of ribosome complex at stop codon;
Marks can be awarded in an annotated diagram.
Accept UAA, UAG or UGA instead of stop codon in mpm or mpn but do not accept terminator sequence.
Do not award mpk for the ribosome moving to the start codon in a 5’ to 3’ direction.
Explanations of translation were generally good, with many of the significant events included. Fewer candidates than in the past included unnecessary information about transcription. A common omission was the presence of a three-base (or nucleotide) anticodon on tRNA and a frequent small error was the idea that during initiation the first tRNA binds to the A site and then moves to the P site, rather than binding to the P site immediately.
