Home / A level Biology 6.2 Protein synthesis – Exam style question – Paper 2

A level Biology 6.2 Protein synthesis – Exam style question – Paper 2

A level Biology Paper 2 - All Chapters
Question

(a) Table 4.1 shows a sequence of 12 nucleotides in the template strand of a short length of a DNA molecule, the corresponding primary transcript and the four amino acids coded for by the sequence. The table is incomplete.

(i) Complete Table 4.1 to show the sequence of nucleotides in the primary transcript that would result from transcription of this short length of DNA.

Table 4.1

(ii) Table 4.2 shows all the possible template strand DNA triplets that code for the amino acids labelled aa1, aa2, aa3 and aa4 in Table 4.1.

Table 4.2

Complete Table 4.3 to identify the four amino acids labelled AA1, AA2, AA3, and AA4 in Table 4.1.

Table 4.3

(iii) One type of gene mutation is caused by the substitution of a DNA nucleotide. Using the information in Table 4.2, state and explain the effect on the final protein structure of a substitution of the nucleotide at position 3 in Table 4.1.

(iv) A second type of gene mutation is caused by the deletion of a DNA nucleotide. Using the information in Table 4.2, state and explain the effect on the final protein structure of a deletion of the nucleotide at position 3 in Table 4.1.

(b) Replication of nuclear DNA occurs just once in every mitotic cell cycle. Six named events associated with the mitotic cell cycle are listed. The events are not listed in any particular order. Draw a circle around each event where replication of nuclear DNA occurs.

Mitotic Cell Cycle Events

(c) Outline how DNA is replicated inside the nucleus.

(d) Fig. 4.1 shows the structure of an ATP molecule.

ATP Molecule Structure

State the name of the part of the ATP molecule labelled A in Fig. 4.1.

▶️ Answer/Explanation
Solution

(a)(i)

Answer to Table 4.1

Explanation: The primary transcript is formed by transcribing the DNA template strand, replacing thymine (T) with uracil (U). The sequence is complementary to the template strand.

(a)(ii)

Answer to Table 4.3

Explanation: The amino acids are identified using Table 4.2. AA1 is valine (CAA), AA2 is leucine (GAA), AA3 is aspartate (CTA), and AA4 is glutamate (CTT).

(a)(iii) No effect on the protein structure because all four triplets beginning with CA code for valine (CAA, CAG, CAT, CAC). This demonstrates the redundancy of the genetic code.

(a)(iv) The deletion causes a frameshift mutation, altering all subsequent codons. The first amino acid (valine) remains unchanged, but the rest of the sequence is disrupted, potentially leading to a non-functional protein.

(b) Replication occurs during interphase and specifically the S phase of the cell cycle.

(c) DNA replication involves unwinding the double helix (via helicase), using both strands as templates, adding complementary nucleotides (via DNA polymerase), and joining fragments (via ligase). The process is semi-conservative.

(d) The part labelled A is ribose, a pentose sugar in ATP.

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