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Biology 30 · Worksheets

Molecular genetics · Set B

Ten questions of mixed difficulty, covering Molecular genetics. Print it, or work through it on screen — the answer key starts on its own page.

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Molecular genetics · Set B

Biology 30 · maddyhelps.com

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  1. In eukaryotic cells, what happens to mRNA before it leaves the nucleus?

    1. a) Introns are removed and exons are joined together
    2. b) It is copied back into DNA
    3. c) It is translated into protein
    4. d) Exons are removed and introns are joined together

  2. A substitution changes a codon from GAA to GAG. Both code for glutamic acid. What kind of mutation is this?

    1. a) a missense mutation
    2. b) a frameshift mutation
    3. c) a nonsense mutation
    4. d) a silent mutation

  3. 30% of the bases in a DNA sample are adenine. What percentage are guanine?

    1. a) 20%
    2. b) 40%
    3. c) 70%
    4. d) 30%

  4. There are 64 codons but only 20 amino acids. What follows from this?

    1. a) 44 codons are never used
    2. b) More than one codon can code for the same amino acid
    3. c) Each codon codes for several amino acids
    4. d) Some amino acids have no codon

  5. A permanent change in the sequence of DNA is called a:

    1. a) chromosome
    2. b) clone
    3. c) mutation
    4. d) codon

  6. DNA replication is called semi-conservative because:

    1. a) the new molecule is completely new
    2. b) only half of the genes are copied
    3. c) half of the DNA is destroyed
    4. d) each new DNA molecule has one original strand and one new strand

  7. What do restriction enzymes do?

    1. a) join pieces of DNA together
    2. b) turn DNA into protein
    3. c) copy DNA many times
    4. d) cut DNA at specific base sequences

  8. Why is a frameshift mutation usually more harmful than a single base substitution?

    1. a) It changes every codon after the mutation
    2. b) It changes the DNA backbone
    3. c) It only affects the stop codon
    4. d) It removes the whole gene

  9. On the lagging strand, DNA is built in short Okazaki fragments. Which enzyme joins them?

    1. a) a restriction enzyme
    2. b) DNA ligase
    3. c) helicase
    4. d) RNA polymerase

  10. Where does translation happen?

    1. a) at a ribosome
    2. b) at the cell membrane
    3. c) in the mitochondria
    4. d) in the nucleus

Answer key · Molecular genetics · Set B

Biology 30 · maddyhelps.com

  1. a) Introns are removed and exons are joined together — Introns are non-coding sections that get cut out; exons, which are expressed, are spliced together into the final message.
  2. d) a silent mutation — The amino acid does not change, so the protein is identical. Redundancy in the genetic code makes silent mutations possible.
  3. a) 20% — A pairs with T, so T is also 30%. That leaves 40% for G and C together, and since they pair, each is 20%.
  4. b) More than one codon can code for the same amino acid — The code is redundant: several codons often share an amino acid, and three are stop codons. This redundancy is why some mutations change nothing.
  5. c) mutation — Mutations can be harmful, helpful or have no effect at all. They are the original source of all new alleles.
  6. d) each new DNA molecule has one original strand and one new strand — The two strands separate and each serves as a template, so every copy keeps (conserves) half of the original molecule.
  7. d) cut DNA at specific base sequences — Each restriction enzyme recognises one short sequence and cuts there. DNA ligase is the enzyme that joins pieces together.
  8. a) It changes every codon after the mutation — Inserting or deleting a base shifts the three-letter reading frame, so every codon from that point on is read wrongly. A substitution changes at most one codon.
  9. b) DNA ligase — DNA polymerase can only build in one direction, so the lagging strand is made in pieces. Ligase seals the gaps between them.
  10. a) at a ribosome — Transcription (DNA to mRNA) happens in the nucleus. The mRNA then travels to a ribosome, where it is translated into a protein.