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3.8.3 Using genome projects

AQA A-level Biology 3.8.3 practice on Using genome projects, with free MCQs, clues and worked explanations drawn from the The control of gene expression section of specification 7402.

Specification route
3.8.3
Question bank
18 questions
Course stage
Year 13 / A-level only

Sample questions

QUESTION 1 · 3.8.3 · LEVEL 2

Why is it relatively easy to determine the proteome of simple organisms like bacteria from their genome sequence?

  • Because prokaryotes do not contain non-coding DNA (introns), so the genome sequence translates directly into the proteome.
  • Because bacteria only produce one type of protein.
  • Because the genetic code in bacteria is not degenerate.
  • Because bacteria do not use mRNA for translation.
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Simple organisms lack the 'junk' DNA that interrupts genes in complex organisms.

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Answer: Because prokaryotes do not contain non-coding DNA (introns), so the genome sequence translates directly into the proteome.

Determining the genome of simpler organisms allows the sequences of the proteins... to be determined. Prokaryotes lack introns and complex regulatory genes, making it straightforward to predict their proteome from their DNA.

QUESTION 2 · 3.8.3 · LEVEL 2

In complex organisms, why does knowledge of the genome not easily translate into knowledge of the proteome?

  • The presence of non-coding DNA and regulatory genes makes it difficult to determine which sequences actually code for proteins.
  • Complex organisms use a completely different genetic code to simple organisms.
  • The proteins in complex organisms are constantly mutating during translation.
  • The genome is continually being altered by retroviruses, making it unpredictable.
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A human has a lot of DNA that doesn't actually produce anything functional.

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Answer: The presence of non-coding DNA and regulatory genes makes it difficult to determine which sequences actually code for proteins.

In more complex organisms, the presence of non-coding DNA and of regulatory genes means that knowledge of the genome cannot easily be translated into the proteome.

QUESTION 3 · 3.8.3 · LEVEL 2

Why is it relatively straightforward to determine the proteome of a simple organism, like a bacterium, directly from its genome sequence?

  • Prokaryotic DNA does not contain non-coding introns, so the genomic base sequence maps directly to the amino acid sequence of its proteins.
  • Bacteria only use one single type of protein for all their metabolic functions.
  • The genetic code in bacteria is completely non-degenerate, meaning each triplet codes for exactly one specific protein.
  • Bacteria do not perform transcription, they translate DNA directly into proteins.
Show clue

Simple organisms lack the 'junk' DNA that interrupts the coding sequences in complex organisms.

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Answer: Prokaryotic DNA does not contain non-coding introns, so the genomic base sequence maps directly to the amino acid sequence of its proteins.

Determining the genome of simpler organisms allows the sequences of the proteins... to be determined. Because prokaryotes do not have non-coding DNA (introns), their genome easily translates to their proteome.

QUESTION 4 · 3.8.3 · LEVEL 2

Why is it difficult to determine the proteome of a complex organism (like a human) directly from its genome sequence?

  • Complex organisms have vast amounts of non-coding DNA (introns) and regulatory genes, meaning the genome sequence does not simply translate directly into functional proteins.
  • The genome of complex organisms constantly mutates during transcription, changing the proteins produced.
  • Complex organisms use a different genetic code than simple organisms, making it impossible to read.
  • The proteins in complex organisms are not produced by DNA, but are absorbed entirely from their diet.
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Only about 1.5% of the human genome actually codes for proteins.

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Answer: Complex organisms have vast amounts of non-coding DNA (introns) and regulatory genes, meaning the genome sequence does not simply translate directly into functional proteins.

In more complex organisms, the presence of non-coding DNA and of regulatory genes means that knowledge of the genome cannot easily be translated into the proteome.

QUESTION 5 · 3.8.3 · LEVEL 1

What is the strict biological definition of an organism's 'genome'?

  • The complete set of genes in a cell, including those in mitochondria and/or chloroplasts.
  • The full range of proteins that a cell is able to produce.
  • Only the coding regions (exons) of the DNA found within the nucleus.
  • The total number of chromosomes found in a diploid somatic cell.
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It encompasses all the genetic information.

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Answer: The complete set of genes in a cell, including those in mitochondria and/or chloroplasts.

The genome is the complete set of genetic material present in a cell or organism, which includes the DNA in the nucleus as well as in organelles like mitochondria and chloroplasts.

QUESTION 6 · 3.8.3 · LEVEL 1

What is the strict biological definition of a 'proteome'?

  • The full range of proteins that a cell is able to produce.
  • The complete set of mRNA transcripts present in a cell at any one time.
  • The entire sequence of nucleotide bases in an organism's DNA.
  • The specific sequence of amino acids in a single polypeptide chain.
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Genome relates to genes; proteome relates to...

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Answer: The full range of proteins that a cell is able to produce.

While the genome is the genes, the proteome is the expression of those genes—the full range of proteins a cell, tissue, or organism can manufacture.

QUESTION 7 · 3.8.3 · LEVEL 3

How is determining the genome (and therefore the proteome) of pathogenic bacteria highly useful in modern medicine?

  • It allows scientists to identify the specific amino acid sequences of the pathogen's surface proteins, which can be synthesized and used as antigens to develop vaccines.
  • It allows doctors to physically destroy the pathogen's DNA using targeted radiation therapy.
  • It proves that bacteria are eukaryotic, allowing them to be treated with standard antivirals.
  • It stops the bacteria from undergoing meiosis, preventing them from reproducing in the body.
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If you know the blueprint of the enemy's 'uniform', you can train the immune system to recognize it.

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Answer: It allows scientists to identify the specific amino acid sequences of the pathogen's surface proteins, which can be synthesized and used as antigens to develop vaccines.

By sequencing a pathogen's genome, we can determine its proteome. This reveals the structure of its surface antigens. We can then manufacture these antigens safely in a lab to use in vaccines, triggering an immune response without causing disease.

QUESTION 8 · 3.8.3 · LEVEL 3

Why is it very difficult to translate the genome of a complex eukaryote (like a human) directly into its proteome?

  • Eukaryotic genomes contain vast amounts of non-coding DNA (introns) within genes, and complex regulatory genes, making it hard to identify exactly which sequences actually code for proteins.
  • Eukaryotic DNA is constantly mutating during translation, so the proteins change every second.
  • Eukaryotic organisms do not use the universal genetic code, so their DNA cannot be read by computers.
  • Eukaryotes have a circular genome that lacks a definitive start and end point.
Show clue

A large percentage of human DNA is sometimes called 'junk' DNA because it doesn't code for polypeptides.

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Answer: Eukaryotic genomes contain vast amounts of non-coding DNA (introns) within genes, and complex regulatory genes, making it hard to identify exactly which sequences actually code for proteins.

In complex organisms, genes are interrupted by non-coding introns, and their expression is controlled by complex regulatory genes. Therefore, simply looking at the DNA sequence does not easily tell you what the final, spliced, functional protein will look like.

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