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Biology 30 · Worksheets

Molecular genetics · Set A

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 A

Biology 30 · maddyhelps.com

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Circle the best answer for each question. Show your work in the space provided.

  1. Which tRNA anticodon pairs with the mRNA codon AUG?

    1. a) TAC
    2. b) AUG
    3. c) UAC
    4. d) CAU

  2. How do scientists get bacteria to make human insulin?

    1. a) Inject insulin protein into bacteria
    2. b) Cut the insulin gene and a plasmid with the same restriction enzyme, join them with ligase, and put the plasmid into bacteria
    3. c) Use PCR to turn bacteria into human cells
    4. d) Fuse a human cell with a bacterium

  3. In gel electrophoresis, which DNA fragments travel the farthest?

    1. a) the fragments with the most adenine
    2. b) the smallest fragments
    3. c) the largest fragments
    4. d) all fragments move the same distance

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

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

  5. Which technique makes millions of copies of a segment of DNA?

    1. a) PCR (polymerase chain reaction)
    2. b) crossing over
    3. c) gel electrophoresis
    4. d) transcription

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

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

  7. What causes sickle cell anemia?

    1. a) A frameshift that deletes the hemoglobin gene
    2. b) A missing chromosome
    3. c) A single base substitution that changes one amino acid in hemoglobin
    4. d) An extra copy of chromosome 21

  8. Which molecule carries amino acids to the ribosome?

    1. a) DNA
    2. b) mRNA
    3. c) tRNA
    4. d) rRNA

  9. What are the three parts of a DNA nucleotide?

    1. a) a phosphate, a deoxyribose sugar and a nitrogenous base
    2. b) an amino acid, a sugar and a fatty acid
    3. c) a base, a codon and an anticodon
    4. d) a phosphate, a ribose sugar and an amino acid

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

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

Answer key · Molecular genetics · Set A

Biology 30 · maddyhelps.com

  1. c) UAC — The anticodon is complementary: A–U, U–A, G–C gives UAC. TAC is wrong because RNA uses uracil, not thymine.
  2. b) Cut the insulin gene and a plasmid with the same restriction enzyme, join them with ligase, and put the plasmid into bacteria — Using the same restriction enzyme gives matching sticky ends, so the gene fits into the plasmid. The bacteria then read the human gene and make insulin — recombinant DNA.
  3. b) the smallest fragments — DNA is negatively charged, so it moves toward the positive end. Small pieces slip through the gel more easily and get farther in the same time.
  4. d) 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. a) PCR (polymerase chain reaction) — PCR repeats cycles of heating and cooling to double the DNA each time. Gel electrophoresis sorts DNA pieces by size; it does not copy them.
  6. d) DNA ligase — DNA polymerase can only build in one direction, so the lagging strand is made in pieces. Ligase seals the gaps between them.
  7. c) A single base substitution that changes one amino acid in hemoglobin — One base change swaps one amino acid in hemoglobin. That small change makes red blood cells bend into a sickle shape — a striking example of a missense mutation.
  8. c) tRNA — Each transfer RNA carries one amino acid and has an anticodon that matches a codon on the mRNA. mRNA is the message being read.
  9. a) a phosphate, a deoxyribose sugar and a nitrogenous base — Sugar and phosphate alternate to form each strand's backbone, and the bases stick inward to pair up. Ribose is RNA's sugar.
  10. b) mutation — Mutations can be harmful, helpful or have no effect at all. They are the original source of all new alleles.