VCE-BIO-U34 4.1 📋 – Practice Exam 1: Question Paper

Which three components make up a single DNA nucleotide?

In DNA, adenine forms hydrogen bonds with which base, and how many hydrogen bonds are formed?

Chargaff’s rules state that in double-stranded DNA:

The two strands of a DNA double helix are described as ‘antiparallel’ because:

The Meselson-Stahl experiment, using density-labelled nitrogen isotopes (15N/14N), provided evidence that DNA replication is:

Which enzyme unwinds the DNA double helix at the replication fork by breaking hydrogen bonds between base pairs?

Single-strand binding proteins (SSBPs) function during replication to:

Primase is required during DNA replication because:

The lagging strand is synthesised discontinuously as Okazaki fragments because:

Which enzyme joins Okazaki fragments together by forming phosphodiester bonds between them?

In prokaryotes, which enzyme removes RNA primers and replaces them with DNA nucleotides?

The ‘proofreading’ function of DNA polymerase relies on its:

Mismatch repair differs from proofreading in that mismatch repair:

Nucleotide excision repair (NER) is primarily responsible for removing:

A person with xeroderma pigmentosum has a defect in which repair pathway, resulting in extreme sensitivity to UV light and a high skin cancer risk?

Telomeres protect chromosomes primarily by:

Telomerase is an enzyme that:

The ‘end-replication problem’ refers to the fact that:

A point mutation that changes a codon but still codes for the same amino acid is called a:

A point mutation that changes a codon to code for a different amino acid is called a:

A point mutation that converts a codon into a premature stop codon is called a:

Which chromosomal mutation involves a segment of a chromosome breaking off, flipping, and reattaching in the reverse orientation?

A chromosomal mutation in which a segment of one chromosome becomes attached to a non-homologous chromosome is called a:

Nondisjunction during meiosis, resulting in gametes with an abnormal chromosome number (e.g. trisomy 21), refers to:

Why is the genetic code described as ‘degenerate’?

The genetic code is described as (near) ‘universal’ because:

The ‘wobble hypothesis’ explains why:

Which codon signals both the start of translation and codes for the amino acid methionine?

Which of the following is NOT a stop codon?

A ribosome is composed of:

Free ribosomes in the cytosol typically synthesise proteins that:

Which of the following is a post-translational modification of a protein?

An operon is best described as:

The lac operon is described as ‘inducible’ because:

The trp operon is described as ‘repressible’ because:

Which molecule acts as a co-repressor in the trp operon system, switching off transcription of tryptophan-synthesising genes when it is abundant?

DNA methylation, an epigenetic modification, typically involves:

Histone acetylation tends to:

X-chromosome inactivation in female mammals, which forms a condensed Barr body, is an example of epigenetic regulation because it:

Genomic imprinting refers to a phenomenon where:

Describe the process of transcription in eukaryotes, including initiation, elongation and termination.

Explain how the lac operon in E. coli is regulated when lactose is absent and when lactose is present.

A segment of DNA template strand has the sequence: 3′-TACGAACTTGCA-5′. Write the mRNA sequence and the amino acid sequence encoded.

Explain why a frameshift mutation is generally more damaging than a point substitution mutation.

Describe two ways in which gene expression can be regulated at the transcriptional level in eukaryotes.

What is alternative splicing and why is it significant for proteome diversity?

Describe how siRNA (small interfering RNA) can silence gene expression. Include the role of the RISC complex.

Explain what is meant by ‘gene expression’ being regulated at multiple levels. Give one example at each of three different levels.

<strong>Extended Response 1: Protein Synthesis (a)</strong><br>Describe the process of translation, including initiation, elongation and termination.

<strong>Extended Response 1: Protein Synthesis (b)</strong><br>Explain the roles of the A, P, and E sites of the ribosome during translation.

<strong>Extended Response 2: Genetic Technologies (a)</strong><br>Describe how polymerase chain reaction (PCR) works. Include the steps in one cycle and explain the role of Taq polymerase.

<strong>Extended Response 2: Genetic Technologies (b)</strong><br>Explain one ethical consideration associated with the use of genetic technologies in medicine or agriculture.

Extended Response 3: DNA Replication Fidelity and Repair

Extended Response 3: DNA Replication Fidelity and Repair (a)
Table 1 shows mutation rates measured in wild-type E. coli and in a mutant strain lacking a functional mutS gene (which encodes a key mismatch repair protein).

Strain | Mutation rate (mutations per 10^8 cell divisions)
Wild-type (mutS+) | 3
mutS-deficient (mutS-) | 450

Calculate the fold-increase in mutation rate of the mutS-deficient strain compared to the wild-type strain, showing your working.

Extended Response 3: DNA Replication Fidelity and Repair

Extended Response 3: DNA Replication Fidelity and Repair (b)
Explain the normal role of mismatch repair (MMR) proteins, such as MutS and MutL homologues, in maintaining the fidelity of the genome during and after DNA replication.

Extended Response 3: DNA Replication Fidelity and Repair

Extended Response 3: DNA Replication Fidelity and Repair (c)
The human homologue of mutS is called MSH2. Inherited (germline) mutations in MSH2 (or related MMR genes such as MLH1) cause Lynch syndrome, a hereditary condition that greatly increases the risk of colorectal and other cancers. Explain, with reference to the function of MSH2, how inheriting one defective MSH2 allele increases an individual’s cancer risk over their lifetime.

Extended Response 3: DNA Replication Fidelity and Repair

Extended Response 3: DNA Replication Fidelity and Repair (d)
Predict and justify what would happen to the frequency of small insertion/deletion (frameshift) mutations in a bacterial strain that is deficient in both mismatch repair and nucleotide excision repair, if this strain is exposed to UV radiation, compared to a wild-type strain exposed to the same UV dose.

Extended Response 4: Epigenetic Silencing of a Tumour Suppressor Gene

Extended Response 4: Epigenetic Silencing of a Tumour Suppressor Gene (a)
A study compared promoter methylation of the BRCA1 tumour suppressor gene and its mRNA expression level in normal breast tissue and in breast tumour tissue from the same patients.

Tissue type | BRCA1 promoter methylation (%) | Relative BRCA1 mRNA expression
Normal breast tissue | 5 | 1.00
Breast tumour tissue | 78 | 0.06

Describe the relationship shown in the table between BRCA1 promoter methylation level and BRCA1 mRNA expression.

Extended Response 4: Epigenetic Silencing of a Tumour Suppressor Gene

Extended Response 4: Epigenetic Silencing of a Tumour Suppressor Gene (b)
Explain the molecular mechanism by which increased DNA methylation at a gene’s promoter region leads to reduced transcription of that gene.

Extended Response 4: Epigenetic Silencing of a Tumour Suppressor Gene

Extended Response 4: Epigenetic Silencing of a Tumour Suppressor Gene (c)
Distinguish between a genetic mutation and an epigenetic change (such as promoter methylation) as mechanisms for loss of tumour suppressor gene function, with reference to reversibility and heritability through cell division.

Extended Response 4: Epigenetic Silencing of a Tumour Suppressor Gene

Extended Response 4: Epigenetic Silencing of a Tumour Suppressor Gene (d)
A drug that inhibits DNA methyltransferase (DNMT) enzymes has been proposed as a treatment to reactivate silenced tumour suppressor genes, such as BRCA1, in cancer cells. Evaluate this therapeutic approach by outlining one potential benefit and one potential limitation.