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Question 1
Nucleic acids include biological molecules such as DNA and RNA. mRNA and tRNA are both types of RNA. |
a) | Describe two differences between the structure of mRNA and the structure of tRNA.
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b) | 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 Use information from the table above to give the amino acid sequence determined by this sequence.
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c) | 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. Does information in this question support this hypothesis? Give reasons for your answer.
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d) | Explain how a single base substitution causes a change in the structure of a polypeptide.
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Question 2
The table below shows part of a pre-mRNA molecule transcribed from a section of DNA. |
a) | Complete the table with the base sequence of the DNA strand from which this pre-mRNA was synthesised.
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b) | What is the maximum number of amino acids this DNA sequence could code for?
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c) | In a eukaryotic cell, the pre-mRNA sequence may be different to the mature mRNA sequence. Explain why.
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d) | Describe how a polypeptide is formed by translation of mRNA.
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Question 3
The table below shows the mRNA codons for different amino acids. For example, the codon GGG codes for the amino acid alanine. |
a) | Use information from the table to explain why the genetic code is described as degenerate.
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b) | Suggest the role of the mRNA codons UGA, UAG, and UAA.
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c) | Suggest one reason why the genetic code is often shown as mRNA codons rather than DNA triplets.
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d) | Describe how mRNA is formed by transcription of DNA in eukaryotic cells.
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Question 4
DNA is a biological molecule used to transmit genetic information from one generation to the next. |
a) | Describe the structure of a DNA molecule.
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b) | The genetic code uses four different nitrogenous bases. What is the maximum number of different DNA triplets that can be made using these four bases?
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c) | 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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d) | DNA is copied during the process of DNA replication. DNA is also used in the process of transcription to form mRNA. Describe the similarities and the differences between the processes of DNA replication and transcription.
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Question 5
DNA sequences consist of regions known as exons and introns. |
a) | Describe the meaning of the term exon.
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b) | DNA sequences code for proteins such as haemoglobin or digestive enzymes. Explain why the process of transcription is needed to synthesise these proteins.
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c) | 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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d) | 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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Question 6
DNA sequences within the nucleus need to be transcribed into mRNA to synthesis proteins. |
a) | Describe the role of RNA polymerase in the process of transcription.
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b) | Some antibiotics are designed to interfere with the process of protein synthesis. The antibiotic actinomycin D works by binding to molecules of DNA directly, whereas the antibiotic α-amanitin works by binding to RNA polymerase. Explain how actinomycin D affects protein synthesis.
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c) | Explain how α-amanitin affects protein synthesis.
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d) | After transcription, mRNA molecules leave the nucleus and travel to the ribosomes. Describe the role of ribosomes in the the synthesis of proteins.
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Question 7
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). |
a) | Describe why the genetic code is described as being universal.
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b) | 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 Use the information above to write the mRNA sequence for the section of DNA in an unaffected individual.
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c) | Use the table and the information above to write out the amino acid sequence coded for by the sequence in an unaffected individual.
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d) | Use the information above to identify the type of mutation that causes sickle cell anaemia.
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e) | Explain how this mutation results in the production of faulty haemoglobin molecules.
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Question 8
The diagram below shows the codons for each amino acid. A DNA base sequence that codes for a protein is shown below: GGT CAC GAA CCT TTA |
a) | Use this sequence and the table above to work out the sequence of amino acids in this protein.
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b) | 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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c) | 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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d) | Use the information above to explain the nature of the genetic code.
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Question 9
The diagram below shows an example of a tRNA molecule. |
a) | Name structures labelled A and B in the diagram above.
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b) | tRNA molecules interact with ribosomes during the process of protein synthesis. Name the two types of molecule a ribosome is made up of.
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c) | Describe how one amino acid is added onto a growing polypeptide chain being synthesised by a ribosome.
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d) | 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
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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d) | DNA is found in both eukaryotic and prokaryotic cells. Describe the similarities and differences between the DNA found in these two types of cells.
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