QUESTION 74 (5 marks)
A muscle cell and a nerve cell contain the same genome but produce different sets of proteins.
a) Explain how transcription factors can contribute to this difference. [3 marks]
b) Explain how different protein sets can contribute to different cell functions. [2 marks]
Practice marking scheme
Answer
a) Different transcription factors bind regulatory/promoter regions and activate or repress different genes. b) Different proteins give cells different structures or activities, such as contraction or signal transmission.
Working
Cell-specific transcription factors can bind DNA near or at promoters and influence recruitment or activity of transcription machinery. Different combinations of active genes produce different mRNAs and protein sets. Proteins perform structural, catalytic and signalling roles, so differences in their abundance support specialised cell function. For example, muscle cells produce abundant contractile proteins.
Marking criteria
- States that transcription factors bind promoter/regulatory DNA. [1 mark]
- Describes activation or repression of transcription. [1 mark]
- Links different factors or factor activity to different expressed genes. [1 mark]
- Links different proteins to different cell structures or activities. [1 mark]
- Provides an appropriate functional example. [1 mark]
Practice question aligned to the current QCAA syllabus; review the worked solution and marking criteria.
View the QCAA syllabusCompare your working with the guide above.