Gene mutations and what they do to a protein

Grade 9 Science Worksheet

Circle the best answer.

1. Read this first

   Original mRNA (model, not to scale), 5′ to 3′, cut into codons

   AUG GGA CUU AAG UAA. Changed mRNA (model), 5′ to 3′, cut into codons: AUG GGA CCU AAG UAA. The marked letter is base 8 of the changed mRNA. Table excerpt of the standard genetic code: AUG, methionine; GGA, glycine; CUU, leucine; AAG, lysine; UAA, stop; CCU, proline.

2. 1.

   Ari translates both model mRNAs. How do the two chains compare?

   • Both have four amino acids; leucine is replaced by proline
   • The chains match, because one letter is too small to matter
   • Both start the same, but the amino acids after the change are different
   • The changed chain stops after glycine, because CCU ends the chain

3. Original mRNA (model, not to scale), 5′ to 3′, cut into codons

   AUG UCU GCU GGA UAA. Changed mRNA (model), 5′ to 3′, cut into codons: AUG UCA GCU GGA UAA. The marked letter is base 6 of the changed mRNA. Table excerpt of the standard genetic code: AUG, methionine; UCU, serine; GCU, alanine; GGA, glycine; UAA, stop; UCA, serine.

4. 2.

   Bo translates both model mRNAs. How many amino acids differ between the chains, and what kind of change is it?

   • No amino acid differs, but the protein is harmed anyway
   • One amino acid differs; the change is missense
   • No amino acid differs; the change is silent
   • Two amino acids are lost; the change is nonsense

5. Original mRNA (model, not to scale), 5′ to 3′, cut into codons

   AUG GAC UUG CAG AAA UAA. Changed mRNA (model), 5′ to 3′, cut into codons: AUG GAC UUG UAG AAA UAA. The marked letter is base 10 of the changed mRNA. Table excerpt of the standard genetic code: AUG, methionine; GAC, aspartic acid; UUG, leucine; CAG, glutamine; AAA, lysine; UAA, stop; UAG, stop.

6. 3.

   Esme translates both model mRNAs. The original chain has five amino acids. How many are in the changed chain?

   • 2 amino acids: the chain ends one codon early
   • 5 amino acids: the message keeps the same length
   • 3 amino acids: the chain ends at UAG, before lysine
   • 4 amino acids: UAG adds one last amino acid, then the chain ends

7. Original mRNA (model, not to scale), 5′ to 3′, not yet cut

   AUGCCUGAUAAAUUUGGA. Copy (model), 5′ to 3′, not yet cut: AUGCCUAUAAAUUUGGA. The marked letter is base 7 of the original mRNA. Read five codons of each strand, starting at AUG. Table excerpt of the standard genetic code: AUG, methionine; CCU, proline; GAU, aspartic acid; AAA, lysine; UUU, phenylalanine; GGA, glycine; AUA, isoleucine; AAU, asparagine; UUG, leucine.

8. 4.

   Kira’s copy of a model mRNA lacks the marked base. Five codons of the copy are read. How many of its five amino acids differ from the original’s first five?

   • 3: the amino acids from the deletion onward
   • 1: just the amino acid at the deletion
   • 2: the amino acids on each side of the deletion
   • 5: the first five amino acids

9. Original mRNA (model, not to scale), 5′ to 3′, not yet cut

   AUGGGAGACCACAACUUC. Copy X (model), 5′ to 3′, not yet cut: AUGCGGAGACCACAACUUC. Copy Y (model), 5′ to 3′, not yet cut: AUGGGAGACCACAACCUUC. The marked letter is base 4 of copy X and base 16 of copy Y. Read six codons of each strand, starting at AUG. Table excerpt of the standard genetic code: AUG, methionine; GGA, glycine; GAC, aspartic acid; CAC, histidine; AAC, asparagine; UUC, phenylalanine; CGG, arginine; AGA, arginine; CCA, proline; CAA, glutamine; CUU, leucine.

10. 5.

    Luz compares two copies of a model mRNA, each with one extra base (marked). Which copy changes more amino acids, and why?

    • X: more codons come after it and are read in the shifted frame
    • Same number: each copy has one extra base, so one amino acid changes
    • Y: its extra base is nearer the end, so more is lost
    • Neither: an extra base is not read, so the chains are unchanged

11. Original mRNA (model, not to scale), 5′ to 3′, cut into codons

    AUG GAU CUG AAA GGC UAA. Copy (model), 5′ to 3′, not yet cut: AUGGAGAAAGGCUAA. The marked letters are bases 6 to 8 of the original mRNA. Table excerpt of the standard genetic code: AUG, methionine; GAU, aspartic acid; CUG, leucine; AAA, lysine; GGC, glycine; UAA, stop; GAG, glutamic acid.

12. 6.

    Noah compares a model mRNA with a copy that lacks three bases (marked in the original). How do the two chains compare?

    • 4 amino acids: two are replaced by one, and lysine and glycine stay
    • 2 amino acids: three bases shorten the chain by three
    • 5 amino acids: just the amino acid at the deletion changes
    • 4 amino acids: the ones after the deletion are different

13. Change card (model data)

    change	what happened to the gene
    P	6 bases added
    Q	1 base added
    R	2 bases removed
    S	4 bases removed

14. 7.

    Pia reads a card of four model changes to one gene. Which change keeps the reading frame of the codons after it?

    • P: 6 bases make two whole codons
    • Q: one base is too few to move the frame
    • S: 4 bases removed leaves whole codons behind
    • No row: any added or removed bases shift the frame

15. Changed DNA template strand (model, not to scale), 3′ to 5′, cut into triplets

    TAC CCT ATC GAA TTT ATT. Changed mRNA, made from the template (model), 5′ to 3′, cut into codons: AUG GGA UAG CUU AAA UAA. Original mRNA (model), 5′ to 3′, cut into codons: AUG GGA CAG CUU AAA UAA. The mRNA pairs with the template strand base by base. The marked letter is base 7 of the changed template. Model plant (not a real gene): the original mRNA builds a pigment enzyme of five amino acids. A plant with the enzyme makes purple pigment and has purple flowers. A plant without the enzyme has white flowers. Table excerpt of the standard genetic code: AUG, methionine; GGA, glycine; CAG, glutamine; CUU, leucine; AAA, lysine; UAA, stop; UAG, stop.

16. 8.

    Ren reads a model gene card for flower color. A plant has the changed DNA. What color are its flowers, and why?

    • White: the enzyme ends after two amino acids, so no pigment is made
    • Purple: the changed codon adds a new amino acid to the enzyme
    • White: the enzyme is full length but has a different amino acid
    • Purple: one changed letter is too small to stop the enzyme

17. Changed DNA template strand (model, not to scale), 3′ to 5′, cut into triplets

    TAC TTG CTA GAG GGA ATT. Changed mRNA, made from the template (model), 5′ to 3′, cut into codons: AUG AAC GAU CUC CCU UAA. Original mRNA (model), 5′ to 3′, cut into codons: AUG AAC GAU CUU CCU UAA. The mRNA pairs with the template strand base by base. The marked letter is base 12 of the changed template. Model plant (not a real gene): the original mRNA builds a pigment enzyme of five amino acids. A plant with the enzyme makes purple pigment and has purple flowers. A plant without the enzyme has white flowers. Table excerpt of the standard genetic code: AUG, methionine; AAC, asparagine; GAU, aspartic acid; CUU, leucine; CCU, proline; UAA, stop; CUC, leucine.

18. 9.

    Tala reads a model gene card for flower color. A plant has the changed DNA. What color are its flowers, and why?

    • White: the changed letter makes a different enzyme
    • Pale purple: the enzyme is made in smaller amounts
    • Purple: the enzyme has the same amino acids, so pigment is still made
    • White: a mutation in the pigment gene is harmful

19. Model plants (model data)

    plant	change to the pigment gene	enzyme	flowers
    A	none	five amino acids	purple
    B	silent substitution	same five amino acids	purple
    C	stop codon at codon 3	two amino acids	white

20. 10.

    Zee reads cards for three model plants. Which statement do the cards support?

    • Plant B has a mutation but the same enzyme; only plant C lost the pigment
    • Plant C makes a longer enzyme, since a stop codon adds amino acids
    • Plant B makes a different enzyme, since its gene has a changed letter
    • Plants B and C both have harmed enzymes, because both have mutations