NCEA Level 2 Biology 91159 Expression free practice questions with answers

Question 1 (15 marks) [Gene expression]

(a) Part of the template (antisense) strand of a gene is shown, written 3′ to 5′: 3′ TAC AGG GGG CAG TAT AAA ATC 5′ (i) Write the base sequence of the mRNA transcribed from this strand (5′ to 3′) and state where transcription occurs in a eukaryotic cell. (ii) Write the anticodon of each tRNA that pairs with the codons of the mRNA, up to but not including the stop codon. (iii) Use the genetic code table supplied (below) to give the amino acid sequence of the polypeptide. (iv) Explain the role of tRNA in translation. Genetic code (mRNA codons): Phe = UUU, UUC; Leu = UUA, UUG, CUU, CUC, CUA, CUG; Ile = AUU, AUC, AUA; Met = AUG; Val = GUU, GUC, GUA, GUG; Ser = UCU, UCC, UCA, UCG, AGU, AGC; Pro = CCU, CCC, CCA, CCG; Thr = ACU, ACC, ACA, ACG; Ala = GCU, GCC, GCA, GCG; Tyr = UAU, UAC; His = CAU, CAC; Gln = CAA, CAG; Asn = AAU, AAC; Lys = AAA, AAG; Asp = GAU, GAC; Glu = GAA, GAG; Cys = UGU, UGC; Trp = UGG; Arg = CGU, CGC, CGA, CGG, AGA, AGG; Gly = GGU, GGC, GGA, GGG; Stop = UAA, UAG, UGA.

(a) Answer: (i) mRNA AUG UCC CCC GUC AUA UUU UAG, nucleus; (ii) anticodons UAC, AGG, GGG, CAG, UAU, AAA; (iii) Met – Ser – Pro – Val – Ile – Phe

• Evidence level: Excellence (complementary base pairing: DNA template → mRNA (A→U, T→A, G→C, C→G), codon → anticodon, codon → amino acid).

• (i) mRNA (5′ to 3′): AUG UCC CCC GUC AUA UUU UAG; transcription occurs in the nucleus (catalysed by RNA polymerase).

• (ii) Anticodons (3′ to 5′): UAC, AGG, GGG, CAG, UAU, AAA.

• (iii) Codons AUG UCC CCC GUC AUA UUU UAG give: Met – Ser – Pro – Val – Ile – Phe (then the stop codon UAG ends translation; no amino acid is added)..

• Achievement: (iv) States that tRNA carries amino acids to the ribosome.

• Merit: Links to the codon: each tRNA has an anticodon that pairs with a specific mRNA codon.

• Excellence: Full explanation: each tRNA molecule carries a specific amino acid at one end and has an anticodon at the other that pairs by complementary base pairing with the matching mRNA codon on the ribosome; this ensures the amino acids are added in the sequence specified by the codons, and peptide bonds join them to form the polypeptide.

(b) A salivary gland cell makes large quantities of the protein amylase. (i) State where in the cell transcription and translation of the amylase gene take place. (ii) Explain the role of the ribosome in the production of amylase. (iii) Explain why two different cell types in the same person (for example a salivary gland cell and a nerve cell) have the same genes but make different proteins.

(b) Answer: (i) transcription in the nucleus, translation at ribosomes; (ii) the ribosome in translation; (iii) different genes are switched on in different cells

• Evidence level: Excellence (link each stage of gene expression to its location and its molecules).

• (i) Transcription occurs in the nucleus; translation occurs on ribosomes in the cytoplasm (on the rough endoplasmic reticulum for proteins that are secreted).

• Achievement: (ii) States that the ribosome is involved in translation.