Question
HLPaper 2
Proteins are an important group of chemicals found in all living organisms.
1.[2]
Draw a molecular diagram to show the formation of a peptide bond.
Verified
Solution
- Two amino acids correctly drawn;
1 mark - Removal/production of molecule shown;
1 mark - Peptide bond labelled between C of C=O and N of N-H;
1 mark
2.[5]
Outline how proteins are digested and the products of protein digestion absorbed in humans.
Verified
Solution
- Digested by peptidases/proteases;
1 mark - Pepsin/pepsinogen/endopeptidase secreted by stomach (lining)/digests proteins in the stomach;
1 mark - Pancreas secretes/pancreatic juice contains endopeptidase/trypsin/peptidase;
1 mark - Endopeptidase digest proteins/polypeptides to shorter chains of amino acids/shorter peptides;
1 mark - Amino acids absorbed by active uptake/transport;
1 mark - In small intestine/ileum;
1 mark - Villi increase the surface area for absorption;
1 mark - Absorbed into bloodstream/into capillaries;
1 mark
3.[6]
Explain how polypeptides are produced by the process of translation.
Verified
Solution
- mRNA is translated;
1 mark - mRNA binds with ribosome/with small subunit of ribosome;
1 mark - tRNA-activating enzymes/aminoacyl tRNA synthetases attach specific amino acid to tRNA;
1 mark - Anticodon of 3 bases/nucleotides on tRNA;
1 mark - Start codon/AUG on mRNA;
1 mark - tRNA carrying first amino acid/methionine binds to P/peptidyl site (when large subunit binds);
1 mark - Anticodon (on tRNA) binds to codon (on mRNA);
1 mark - Complementary base pairing (between codon and anticodon);
1 mark - tRNA for next codon binds to A site/amino acyl site;
1 mark - Peptide bond forms between amino acids (on tRNAs) at P and A sites;
1 mark - Ribosome moves along mRNA to next codon/by three bases/in 5' to 3' direction;
1 mark - tRNA released from E/exit site;
1 mark - Process/cycle repeats to elongate the polypeptide/until stop codon is reached;
1 mark - Release of polypeptide and mRNA/disassembly of ribosome complex at stop codon;
1 mark
