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CAIE A-Level Biology 6 Nucleic Acids & Protein Synthesis

Practise moving between nucleotide structures, DNA replication, base sequences, transcription, translation and mutation evidence.

Syllabus
2028–2030
Course
Biology 9700
Level
AS

Covered syllabus points

6.1 Structure of Nucleic Acids and DNA Replication6.2 Protein Synthesis

6. Nucleic Acids and Protein Synthesis question 1

[Maximum number: 1]

The diagrams show the chemical structure of four bases.

1

1

2

2

3

3

4

4

Which diagrams show thymine and cytosine?

A

1 and 2

B

1 and 4

C

2 and 3

D

3 and 4

6. Nucleic Acids and Protein Synthesis question 2

[Maximum number: 6]

DNA and RNA are polynucleotides.

Question (a)

(a)

Describe three ways in which the structure of messenger RNA (mRNA) differs from the structure of DNA.

In each of your answers, include information about the structure of mRNA and the structure of DNA.

1.

2.

3

[ 3 ]

Question (b)

(b)

Scientists have synthesised four synthetic bases, Z, P, S and B . The base pairings of the synthetic bases are shown in Fig. 6.1.

Fig. 6.1

Fig. 6.1

[ 3 ]

Question (i)

(i)

State the letters that represent the two purine synthetic bases in Fig. 6.1.

[ 1 ]

Question (ii)

(ii)

State and explain which DNA base pair is most similar to the synthetic base pairs in Fig. 6.1.

[ 2 ]

6. Nucleic Acids and Protein Synthesis question 3

[Maximum number: 4]

Smooth muscle is a tissue composed of smooth muscle cells. The cells contain cytoplasm packed with proteins that are involved in contraction and relaxation.

Question (a)

(a)

Caldesmon is a large protein with a number of binding sites to attach to other proteins.

Caldesmon exists in two different forms, H-caldesmon and L-caldesmon.
H-caldesmon helps to regulate contraction and relaxation in smooth muscle cells.
L -caldesmon is found in some non-muscle cells, where it also acts as a regulatory protein.
- Caldesmon is coded for by a gene known as CALD1.
- CALD1 has 17 exons.
- The primary structure of H-caldesmon has a repeating sequence in the middle of the amino acid chain that is not present in L-caldesmon.

[ 4 ]

Question (i)

(i)

Researchers have discovered that a gene mutation is not the cause of the two different forms of caldesmon.

Explain what is meant by a gene mutation.

[ 2 ]

Question (ii)

(ii)

Researchers now know that the two different forms of caldesmon are the result of events occurring directly after transcription of DNA. Changes occur to the primary transcript that is formed by DNA transcription.

Suggest how the smooth muscle cells and non-muscle cells can produce different forms of caldesmon from the same primary transcript.

[ 2 ]
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