Gene mutations and what they do to a protein
Grade 9 Science Worksheet - Challenge Me
Circle the best answer.
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.
Ari reads the lactase card. Where is the single-letter change?
- In the lactase protein, because a changed letter changes the protein
- 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 an LCT codon, where it swaps one amino acid in lactase
Bo reads the lactase card. What does the single-letter change do?
- It keeps the LCT gene active, so lactase is still made
- It makes less lactase, because a changed letter breaks a gene
- It changes the lactase protein, because a changed letter changes a protein
- It builds a new lactase with a different amino acid that works longer
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
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.
Jun reads a card of four model changes. Which conclusion do the rows support?
- Mutations are harmful, but some harm more than others
- A mutation alters the protein, and the size of the alteration differs
- Mutations can have no effect, stop a protein, or give a new trait
- An organism makes a mutation when it needs a new trait
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.
Kira reads a card of four model substitutions. Which row is a mutation with no effect on the protein, and why?
- Row 1: just the third letter changed, so it cannot matter
- Row 3: UGA is another amino acid, so the chain keeps its length
- No row: a changed letter changes the amino acid
- Row 2: GAA and GAG both code for glutamic acid
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.
Luz reads a model mouse card. What does the card show about this mutation?
- It gives a new trait, and the mouse grows as before
- It appeared because the mouse needed a darker coat
- 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
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 Milo reviews a classmate’s notebook on mutations. Exactly one line is wrong. Which line, and why?
- 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
- Line 2, because a missense change leaves the chain the same
- Line 1, because a changed base changes the amino acid
Pia reviews a classmate’s notebook on mutations. Exactly one line is wrong. Which line, and why?
- Line 2, because UV light, not DNA polymerase, makes thymine dimers
- Line 3, because deleting three bases shifts the frame
- Line 4, because an error counts as a mutation just when it is harmful
- Line 1, because repair fixes the errors, so no error is left
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.
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 the frame stays and one amino acid is added
- The enzyme is likely to lose its job, because added bases are harmful
- 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 the added bases shift the frame
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 Zee reads a card about two nonsense changes to a model enzyme gene. Which claim and reason go together?
- X and Y have the same effect, because each changes one letter
- Y changes the enzyme more, because its stop codon adds amino acids at the end
- 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