Gene mutations and what they do to a protein

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. Read this first

   Use this

   Lactase card (facts from NIH MedlinePlus Genetics, simplified), 4 rows. Columns: item, what the card says. LCT gene, Gives instructions for making lactase, an enzyme that digests lactose, a sugar in milk. Control region, A short stretch of DNA near LCT that helps control how active the LCT gene is. Most humans, Make less lactase as they get older, because the LCT gene becomes less active after infancy. A single-letter change in the control region, Keeps the LCT gene active, so lactase is still made in adulthood.

2. 1.

   Ari reads the lactase card. Where is the single-letter change?

   • In the start codon of LCT, so lactase begins at a new place
   • In a control region near LCT, not in a codon of the lactase protein
   • In the lactase protein, because a changed letter changes the protein
   • In an LCT codon, where it swaps one amino acid in lactase
3. 2.

   Esme reads the lactase card. Which label fits the single-letter change best?

   • Silent: the codon still codes for the same amino acid in lactase
   • None of the three: it is in a control region, not in a codon
   • Missense: lactase gets a different amino acid
   • Nonsense: a new stop codon ends the lactase chain

4. Use this

   Change card (model data), 4 rows. Columns: change, what happens to the protein, effect on the organism. 1: silent substitution, same amino acids, none noticed. 2: stop codon early in an enzyme gene, enzyme ends early, enzyme does not work. 3: missense in a model coat-color gene, one amino acid differs, darker coat. 4: three-base insertion, one amino acid added, none noticed.

5. 3.

   Jun reads a card of four model changes. Which conclusion do the rows support?

   • Mutations are harmful, but some harm more than others
   • An organism makes a mutation when it needs a new trait
   • Mutations can have no effect, stop a protein, or give a new trait
   • A mutation alters the protein, and the size of the alteration differs

6. Use this

   Codon card (model data), 4 rows. Columns: row, codon before, codon after. 1, UUU, UUA. 2, GAA, GAG. 3, UGG, UGA. 4, AAA, AAU. Table excerpt of the standard genetic code: UUU, phenylalanine; UUA, leucine; GAA, glutamic acid; GAG, glutamic acid; UGG, tryptophan; UGA, stop; AAA, lysine; AAU, asparagine.

7. 4.

   Kira reads a card of four model substitutions. Which row is a mutation with no effect on the protein, and why?

   • No row: a changed letter changes the amino acid
   • Row 2: GAA and GAG both code for glutamic acid
   • Row 1: just the third letter changed, so it cannot matter
   • Row 3: UGA is another amino acid, so the chain keeps its length

8. Use this

   Model mouse card (model data), 5 rows. Columns: item, what the card says. Gene, a model pigment gene in a model mouse. Change, one base replaced, so one amino acid differs. Enzyme, still works. Coat, darker than before. Growth, the mouse grows as before.

9. 5.

   Luz reads a model mouse card. What does the card show about this mutation?

   • It is harmful, because a changed amino acid stops the enzyme
   • It must add a stop codon, since a stop codon is what gives a new trait
   • It gives a new trait, and the mouse grows as before
   • It appeared because the mouse needed a darker coat

10. Notebook (model data)

    line	what it says
    1	A silent substitution changes a base but not the amino acid
    2	A missense substitution swaps one amino acid for another
    3	A frameshift changes the codons from the change onward
    4	Adding three bases always shifts the reading frame

11. 6.

    Milo reviews a classmate’s notebook on mutations. Exactly one line is wrong. Which line, and why?

    • Line 2, because a missense change leaves the chain the same
    • Line 1, because a changed base changes the amino acid
    • Line 4, because three bases make a whole codon and the frame stays
    • Line 3, because a frameshift changes just the next amino acid in the chain
12. 7.

    Noah reviews a classmate’s notebook on mutations. Exactly one line is wrong. Which line, and why?

    • Line 2, because a changed letter changes the protein
    • Line 1, because a stop codon adds amino acids
    • Line 3, because some mutations have no effect or give a new trait
    • Line 4, because UV light works through DNA polymerase

13. Use this

    Deletion card (model data), 3 rows. Columns: item, what the card says. Message, 10 codons, 30 bases. Change P, 1 base deleted from codon 3; 29 bases left. Change Q, 3 bases deleted from codon 3; 27 bases left.

14. 8.

    Ren reads a card about two deletions in a model message. Which claim and reason go together?

    • P changes more amino acids, because 29 bases is longer than 27 bases
    • Q changes more amino acids, because three bases shift the frame by a codon
    • P changes more amino acids, because it shifts the frame for the codons after it
    • P and Q change one amino acid each, because each deletes bases from just one codon

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

    AUG CAC GGA UUU GAG UAA. Copy (model), 5′ to 3′, cut into codons: AUG CAC GGA CCU UUU GAG UAA. The marked letters are bases 10 to 12 of the copy. Table excerpt of the standard genetic code: AUG, methionine; CAC, histidine; GGA, glycine; UUU, phenylalanine; GAG, glutamic acid; UAA, stop; CCU, proline.

16. 9.

    Tala compares a model enzyme gene with a copy that has three extra bases (marked). Which claim and reason go together?

    • The enzyme is likely to keep its job, because an insertion changes just one amino acid
    • The enzyme is likely to lose its job, because added bases are harmful
    • The enzyme is likely to keep its job, because the frame stays and one amino acid is added
    • The enzyme is likely to lose its job, because the added bases shift the frame

17. Nonsense card (model data)

    change	stop codon appears at	amino acids in the chain
    none (original)	codon 12	11
    X	codon 3	2
    Y	codon 11	10

18. 10.

    Zee reads a card about two nonsense changes to a model enzyme gene. Which claim and reason go together?

    • Y changes the enzyme more, because its stop codon adds amino acids at the end
    • X and Y have the same effect, because each changes one letter
    • X is more likely to stop the enzyme working, because it removes nine amino acids and Y one
    • Y is more likely to stop the enzyme working, because it is nearer the end