Cambridge OCR A Level · Biology A - H420
5 multiple-choice questions marked as you go, and 4 written questions with worked solutions. All on Cellular control.
A specific mutation in a eukaryotic gene results in the replacement of a single nucleotide within an intron. Which of the following is the most likely effect of this mutation on the final protein product?
I. The primary mRNA transcript will have an altered sequence.
II. The mature mRNA sequence will definitely be different.
III. The protein might remain unchanged if the splicing process is unaffected.
Cyclic AMP (cAMP) plays a crucial role in post-translational control. Which of the following best describes its mechanism of action in this context?
In the lac operon of Escherichia coli, a mutation in the operator region prevents the repressor protein from binding. What is the effect on the metabolism of the cell in the absence of lactose?
During the development of a vertebrate embryo, the formation of individual digits (fingers and toes) requires a precise balance between cell proliferation and cell death. Which of the following describes the role of apoptosis in this process?
Homeobox gene sequences are highly conserved across different kingdoms. Which statement correctly describes the role of Hox genes in the development of an organism?
Explain why a mutation involving the deletion of a single nucleotide in the DNA sequence of a gene is generally more harmful than a substitution mutation.
Write your answer out first, then check it against the worked solution.
Explain how a mutation in the lacI gene, which results in a repressor protein that can no longer bind to the inducer molecule allolactose, would affect the transcription of the structural genes in the lac operon when lactose is present.
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In the context of the lac operon in Escherichia coli, explain the structural and functional consequences of a mutation that prevents the repressor protein from binding to the operator region in the absence of lactose.
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(a) The lac operon in Escherichia coli is a classic example of transcriptional control. Under conditions where glucose is absent and lactose is present, the operon is expressed.
Describe the specific structural changes and molecular interactions that occur at the lac operon when lactose (or its isomer allolactose) is introduced to the environment, and explain how this leads to the production of enzymes required for lactose metabolism. (3 points)
(b) In eukaryotic cells, gene expression is also regulated at the post-transcriptional level. One significant process is the editing of primary mRNA.
Explain the process of splicing, including what is removed and what is joined, and describe how this process can allow a single gene to code for more than one unique protein. (3 points)
(c) Homeobox genes, such as Hox genes, are highly conserved across diverse animal kingdoms. Explain why these genes are considered to be 'highly conserved' and state their fundamental role in the development of an organism's body plan. (2 points)
Write your answer out first, then check it against the worked solution.
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