QUESTION 5 (5 marks)
a) Describe the roles of messenger RNA and transfer RNA in protein synthesis.
[2 marks]
b) Explain how transcription factors control cell differentiation, using an example.
[3 marks]
QCAA guide · typeset solution
QCAA sample response and mark allocation
5a) | Messenger RNA (or mRNA) provides copies of the gene from the DNA template strand. Transfer RNA (or tRNA) decodes mRNA sequences by matching amino acids to codons of the mRNA. | • describes the role of messenger RNA in protein synthesis [1 mark] • describes the role of transfer RNA in protein synthesis [1 mark] |
5b) | Transcription factors are proteins that turn specific genes on or off by binding to nearby sections of DNA. This allows different genes to be expressed in different cell types. For example, the SRY gene on the Y chromosome promotes the development of testes by producing a protein that regulates the expression of genes (production of proteins) required by Sertoli cells. | • recognises that transcription factors regulate gene expression by binding to specific DNA sequences [1 mark] • explains that this allows for differential gene expression [1 mark] • provides an example [1 mark] |
QCAA sample response and marking criteria reproduced from the official guide.
Compare your working with the guide above.