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Question 1
The body plan of multicellular organisms is determined by DNA. |
a) | Some regions of DNA are non-coding. Explain why.
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b) | Name the type of gene that controls the development of body plans in eukaryotic organisms.
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c) | The expression of genes is influenced by proteins known as transcription factors. Describe the role of transcription factors.
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d) | Scientists often use fruit flies to investigate the genes that control the development of body plans. Suggest two reasons why fruit flies are used for this purpose.
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Question 2
Steroid hormones, such as oestrogen, can influence the genome of a cell. |
a) | What is a genome?
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b) | In the cytoplasm, oestrogen binds to a specific androgen receptor. Suggest and explain why oestrogen only binds to specific receptors.
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c) | The binding of oestrogen to an androgen receptor changes its shape, causing the oestrogen-receptor complex to enter the nucleus and stimulate gene expression. Suggest how the oestrogen-receptor complex could stimulate gene expression.
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d) | Oestrogen can stimulate the growth of some types of breast tumour. A drug known as tamoxifen can be used to treat these tumours. In the liver, tamoxifen is converted into a substance known as endoxifen which has a similar shape to oestrogen. Suggest how endoxifen may reduce the growth rate of breast tumours.
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Question 3
The diagram below shows the lac operon found within the genome of E. coli. This operon contains both structural and regulatory genes. lacA is a structural gene that codes for a protein called transacetylase.
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a) | Describe the difference between structural and regulatory genes.
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b) | Name sections A and B of the lac operon shown in the diagram above.
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c) | Sections C and D of the lac operon shown above code for enzymes. Name sections C and D in the diagram above and describe the function of the enzymes coded for by each section.
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d) | Describe and explain how the absence of lactose affects gene expression within the lac operon.
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Question 4
RNA produced from one gene can give rise to more than one type of protein. The diagram below shows a part of this process.
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a) | Use the diagram above to explain how RNA from one gene can produce more than one type of protein.
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b) | Beta cells in the pancreas produce the protein insulin to control blood glucose concentration. Transcription factors are involved in the activation of the insulin gene. Explain how transcription factors activate this gene.
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c) | Explain why beta cells can produce insulin but other cells within the pancreas cannot.
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Question 5
The diagram below shows the mechanism of action for a transcription factor that increases transcription. |
a) | Name region A in the diagram above.
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b) | Name enzyme B in the diagram above.
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c) | Use the diagram above to explain how transcription factors can increase the rate of transcription.
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d) | Some transcription factors are activators, meaning they increase the rate of transcription. Explain how a transcription factor may function as a repressor.
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Question 6
The diagram below shows the functioning of the lac operon when bacteria are exposed to lactose.
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a) | The lac operon consists of structural and regulatory genes. Name the products of two structural genes within the lac operon.
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b) | Gene I is located a short distance away from the lac operon. The product of this gene is a constitutive protein. What is a constitutive protein?
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c) | Explain how the presence of lactose affects gene expression in the lac operon.
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d) | The structural genes of the lac operon are not expressed in the absence of lactose. Explain why this is beneficial to E. coli.
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Question 7
The diagram below shows the trp operon found in many prokaryotes.
The gene trpA codes for the enzyme tryptophan synthase. This enzyme catalyses the formation of the amino acid tryptophan. |
a) | Explain why tryptophan synthase is an example of a repressible enzyme.
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b) | Describe three similarities between the structure of the lac operon and the trp operon.
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c) | Describe two differences between the functioning of the lac operon and the trp operon.
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d) | A strain of bacteria has been produced with a mutation in the trpR gene, resulting in a non-functional repressor protein. Suggest a negative effect that this mutation will have on this strain of bacteria.
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Question 8
The table below shows the mRNA codons that result in different amino acids. For example, the codon UUC codes for the amino acid phenylalanine (Phe). Sickle cell anaemia is a disease caused by mutations in the beta chain of the haemoglobin protein. The sequences below show sections of DNA sequence coding for the beta chain in an affected and unaffected individual. DNA sequence in unaffected individual: TGA GGA CTC DNA sequence in affected individual: TGA GGA CAC |
a) | Use the information above to identify the type of mutation that causes sickle cell anaemia.
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b) | Explain how this mutation results in the production of faulty haemoglobin molecules.
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c) | A DNA base sequence that codes for a protein is shown below: GGT CAC GAA CCT TTA Scientists identified a mutation that results in the first thymine base being substituted for an adenine base. Explain how this mutation would affect the structure of the protein.
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d) | Scientists identified another mutation that results in the deletion of the fifth nucleotide in the sequence. Explain how this mutation would affect the structure of the protein.
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Question 9
The table below shows the mRNA codons for some different amino acids. Below is the DNA template sequence used to determine the sequence of five amino acids. CAT CCT CCC CGC CAA A mutation in the DNA sequence shown above produced the following amino acid sequence: valine glycine glycine valine valine A student hypothesised that the mutation involved the deletion of one nucleotide within the DNA sequence. |
a) | Does information in this question support this hypothesis? Give reasons for your answer.
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b) | Explain how a single base substitution causes a change in the structure of a polypeptide.
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c) | Mutations in the DNA sequence can impact the structure of proteins produced in translation. Describe the different types of mutation that can occur and explain how they may result in a shortened polypeptide.
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Question 10
DNA sequences consist of regions known as exons and introns. |
a) | Describe the meaning of the term exon.
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b) | The diagram below shows part of a pre-mRNA molecule. Scientists have identified two mutations that commonly affect this region of pre-mRNA. Mutation 1 is a single base substitution. Explain how this mutation might affect the protein coded for by this pre-mRNA.
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c) | Mutation 2 is a deletion of two nucleotides. Explain how this mutation might affect the protein coded for by this pre-mRNA.
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d) | In a eukaryotic cell, the pre-mRNA sequence may be different to the mature mRNA sequence. Explain why.
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e) | Mutations such as substitutions, deletions, or insertions can affect the DNA sequence. However, not all mutations cause a change in protein structure. Give two reasons why.
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Question 11
The genome of a cell refers to the complete set of genes within a cell. |
a) | Define gene mutation.
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b) | Suggest two ways a gene mutation can have no effect on an individual.
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c) | Explain how a gene mutation can have a positive effect on an individual.
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Question 12
The diagram below shows how hormones and transcription factors can control transcription of a gene.
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a) | Name region X in the diagram above.
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b) | Use the diagram above to describe how transcription can be controlled in eukaryotes.
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c) | Explain how gene expression can be regulated after the process of transcription.
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