Genome projects and sequencingAQA A-Level Biology: Subtopic test

1. 1
   Researchers sequenced the genome of a disease-causing bacterium. It has a single circular chromosome of 2.2 million base pairs and about 2,000 genes. The team wants to identify proteins on the surface of the bacterium that could be used as antigens in a vaccine.

   (a)

   What is meant by the genome of the bacterium?

   [1 mark]

   • AAll of the proteins that it can make
   • BOnly the genes that code for antigens
   • CThe complete set of genes/DNA in the cell
   • DThe base sequence of a single gene

   (b)

   What is meant by the proteome of the bacterium?

   [1 mark]

   • AThe full range of proteins that the cell is able to produce
   • BThe complete set of DNA in the cell
   • COnly the enzymes used in respiration
   • DThe amino acid sequence of one protein

   (c)

   Explain how knowing the genome of the bacterium allows potential antigens for a vaccine to be identified.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   The human genome contains about 3.2 billion base pairs. Only about 1.5% of this DNA codes for proteins, and there are about 20,000 protein-coding genes. A human cell can produce many more different proteins than there are genes, and different cell types produce very different sets of proteins from the same genome.

   (a)

   Which statement explains why the human proteome cannot easily be worked out from the genome?

   [1 mark]

   • AHuman cells contain no mRNA
   • BThe genetic code is different in humans
   • CHuman DNA cannot be sequenced
   • DMuch of the DNA is non-coding and there are regulatory genes

   (b)

   What is the role of a regulatory gene?

   [1 mark]

   • AIt codes for the structural proteins in cell membranes
   • BIt codes for a product that switches other genes on or off
   • CIt codes for ribosomal RNA only
   • DIt carries amino acids to the ribosome

   (c)

   Explain why only part of the human genome can be used to predict the proteins produced by a cell.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   During an outbreak of a new bacterial disease, scientists used automated sequencing machines to read the whole genome of the bacterium in two days. The first human genome took 13 years to sequence, but sequencing methods have been continuously updated and now cost far less.

   (a)

   Suggest three benefits of automated sequencing methods compared with the methods used in the first human genome project.

   [3 marks]

   (b)

   Explain how sequencing the genome of the new bacterium could lead to a vaccine against the disease.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A scientist compares two genomes. The bacterium Escherichia coli has 4.6 million base pairs, about 4,300 protein-coding genes, and about 88% of its DNA codes for protein. The human genome has 3.2 billion base pairs, about 20,000 protein-coding genes, and about 1.5% of its DNA codes for protein. A vaccine company wants to use genome data to identify antigens of bacterial pathogens.

   (a)

   Compare how easily the proteome can be determined from the genome of the bacterium and from the human genome.

   [6 marks]

   (b)

   Evaluate the use of genome sequencing to identify antigens for vaccines against bacterial pathogens.

   [6 marks]

   Total for question 4: 12 marks

End of questions