Biology

The diagram shows a simplified version of the process of polypeptide synthesis.

Explain the importance of mRNA and tRNA in polypeptide synthesis.

The diagram shows a simplified version of the process of polypeptide synthesis.
Compare Process A with DNA replication.

Below is a diagram of a process during protein synthesis
Determine the DNA sequence that codes for the amino acid “Asp”.
(A) CTA
(B) CUA
(C) GAT
(D) GAU

Which epigenic mechanism can repress gene expression?
(A) Methylation of DNA
(B) Acetylation of histones
(C) Transcription of non-coding RNAs
(D) Chromosomal recombination

Human papillomavirus (HPV) is a group of viruses that infect the skin and mucous membranes of humans. HPV viruses are classified into different serotypes based on the DNA sequences of their viral genomes. Each HPV type is identified by a specific number (e.g., HPV-16, HPV-18, etc.). HPV types can cause changes in the cells of the cervix, leading to the development of precancerous lesions. If these lesions are left untreated, they may progress to invasive cervical cancer. HPV binds to the surface of epithelial cells and gain entry via endocytosis. Once inside the cell it introduces its viral DNA into the cells nucleus. It uses the hosts cell’s machinery to produce a viral E6 protein. Schematic of HPV infection of a epithelial cell Adapted from Human Papillomavirus and Oropharynx Cancer: Biology, Detection and Clinical Implications

With reference to protein synthesis, explain how infection of high risk HPV strains can lead to cervical cancer. The graph below shows the ten year cumulative incidence rate of cervical precancer by different HPV serotypes. Patients were tested for HPV at the beginning of the 10 year period.

The following diagram represents a short section of DNA.
What are the components labelled X, Y and Z ?

Outline the ways in which the DNA of prokaryotes and eukaryotes differ.

Streptomycin is an antibiotic that kills bacteria by interfering with the function of their ribosomes. The primary effect of the antibiotic is that it prevents the bacteria from producing
A. tRNA.
B. mRNA.
C. amino acids.
D. polypeptides.

The coiled-coil was one of the earliest tertiary protein structures described and first discovered in the two-stranded coiled-coil protein (CC) alpha-keratin. Coiled-coils consist of two or more alpha-helices winding around each other.
Figure 1: Coiled-coil
Such proteins are involved in a wide variety of structural and mechanical processes in cells. Long-CC (LCC) includes long coiled-coils with a minimum stretch of 70 amino acids in one coiled coil and a minimum stretch of 50 amino acids in the other.
A study was carried out to compare the presence of CC and LCC proteins in species from different kingdoms. The graph below represents the estimated percentages of CC proteins, LCC proteins and superlong CC per genome for 22 different species.
Figure 2: % coiled-coil proteins per genome for 22 species. A: Archaea; B: Gram positive bacteria; C: Gram negative bacteria; D: Fungi; E: Animals; F: Plants

“Animals are more closely related to plants than other kingdoms”. Analyse the data provided and assess whether this statement is supported.

Agrobacterium tumefaciens is a rod-shaped bacterium found in soil. Its flagella allow it to move through the soil in response to chemicals released by wounded plant cells. Once it enters its plant host, it injects a section of its DNA called the T-DNA which is derived from its Ti (tumour inducing) plasmid into its host causing the host to form undifferentiated (tumour) tissue termed a crown gall. Figure 1: Crown gall The interaction between a plant and Agrobacterium is detailed below: (A) Agrobacteria cells produce the hormones cytokinin and auxin, which increase host susceptibility and inhibit H2O2 production and hypersensitive response (HR) upon infection. (B) After integration of the bacterial T-DNA into the plant genome, cytokinin and auxin are synthesized by T-DNA encoded enzymes and accumulate inside the tumour. (C) This causes massive changes in the gene expression pattern resulting in metabolomic and morphological adaptations that are necessary for tumour growth and differentiation. (D) Loss of water is minimized by an increase in the levels of the stress hormone ABA. Evaporation of water from the disrupted crown gall surface drives the flow of water and minerals into crown galls. (E) Because photosynthesis is downregulated, the O2 levels are low, the tumour produces C and N compounds heterotrophically and gains energy mainly anaerobically by alcoholic fermentation. (F) The developing tumour becomes a metabolic sink for the host plant, which accumulates metabolites produced by source leaves and minerals taken up by the roots. (G) Auxin and cytokinin also cause an increase in ethylene (ET) which together with salicylic acid (SA) inhibits agrobacterial virulence. (H) ABA induces DNA methylation of the plant genome, regulating gene expression of drought- stress responsive genes. The oncogenes of the T-DNA remain unaffected by methylation of the plant genome.

“Regulation of genes affects the phenotype of the organism.” Discuss this statement using the information provided.

Agrobacterium tumefaciens is a rod-shaped bacterium found in soil. Its flagella allow it to move through the soil in response to chemicals released by wounded plant cells. Once it enters its plant host, it injects a section of its DNA called the T-DNA which is derived from its Ti (tumour inducing) plasmid into its host causing the host to form undifferentiated (tumour) tissue termed a crown gall.
Figure 1: Crown gall

Compare the forms in which DNA is found in agrobacterium and its host before infection.

Which row of the table best describes DNA in both prokaryotic and eukaryotic cells? Prokaryotic Eukaryotic

Analysis of DNA shows that adenine and guanine always make up 50% of the total amount of nitrogenous bases in DNA. Which structural feature of DNA does this provide evidence for?
A. DNA is helical in structure.
B. DNA is always a double-stranded molecule.
C. DNA always has adenine paired with guanine.
D. DNA is made up of equal amounts of nitrogenous bases.

There are about 10 million single nucleotide polymorphisms (SNPs) found in the human genome. Four SNPs are modelled in the diagram.
The SNPs modelled do not affect the phenotype of the individuals shown. Which is the best explanation for this?
A. Only one nucleotide is different at each SNP.
B. The SNPs are part of DNA that is not expressed.
C. AGA, CAA, TAT and CTC all code for the same amino acid.
D. The SNPs are present on one strand of the DNA molecule only.

This chart illustrates three correlation patterns indicating the influence of genes and environment on different traits in individuals.
What does the data show about how genes and family environment affect the three traits?

After infection the virus reproduces in muscle cells near the bite site and in the central nervous system. This requires the single-stranded rabies RNA to be transcribed, translated and replicated in the cytoplasm of host cells. These processes are shown in Diagram 2. Use the information provided in Diagrams 1 and 2 to explain the role of viral RNA polymerase in the reproduction of the virus.

The following DNA base sequence is used to code for a sequence of four amino acids.
CGC ATC ATG CTA
Which of the following correctly represents the anticodons on the transfer RNA during synthesis of this string of amino acids?
A. GCG UAG UAC GAU
B. CGC AUC AUG CUA
C. CGC ATC ATG CTA
D. GCG TAG TAC GAT

Alzheimer’s disease causes destruction of brain tissue, dementia and eventually death. The diagram shows the effect of Alzheimer’s disease on the brain.
The gene with the greatest known effect on the risk of developing late-onset Alzheimer’s disease is called APOE. It is found on chromosome 19.
The APOE gene has multiple alleles, including e2, e3 and e4.
The table shows the risk of developing Alzheimer’s disease for various APOE genotypes compared to average risk in the population.

Analyse the data to assess the risk of developing Alzheimer’s disease associated with the e2, e3 and e4 alleles.

Alzheimer’s disease causes destruction of brain tissue, dementia and eventually death.
The diagram shows the effect of Alzheimer’s disease on the brain.
Amyloid beta protein is produced in the human brain throughout life. In people with Alzheimer’s disease, it accumulates in excessive amounts.
Outline the main steps that brain cells use to make proteins such as amyloid beta.