Use the mRNA codon chart below to answer the question below.

Very rarely, a copying error will result in the substitution of a different nucleotide in the DNA strand, which will cause incorrect mRNA to carry the wrong sequence of bases. Which answer choice below would result in the wrong amino acid being incorporated into the protein? The correct mRNA sequence is CAU GAG CCC.

A. CAC GAG CCC
Incorrect. CAC and CAU both code for the same amino acid, histidine

B. CAU GAG CCG
Incorrect. The 3 codons still code for histidine, glutamate, and proline

C. CAU GUG CCC
Correct! GUG instead of GAG causes valine to be substituted for glutamate.

D. CAC GAG CCA
Incorrect. These 3 codons still code for histidine, glutamate, and proline.

Why don’t all mutations in DNA produce changes in amino acids?

A. Only changes to reproductive cells can cause changes in amino acids.
Incorrect. Any damage to DNA can potentially change the code for an amino acid, whether or not it is inheritable.

B. Since codons for amino acids are made of 3 nucleotide bases, a change can only occur if all 3 bases are wrong.
Incorrect. Even one wrong base—for instance, AUA for AUG-- can sometimes cause the wrong amino acid to be put into a protein.

C. There are many combinations of nucleotide base letters that don’t correspond to amino acids.
Incorrect. Out of the 64 possible 3 letter combinations, all but 3 code for amino acids.

D. An amino acid can have more than one codon.
Correct! Proline, for example, is coded for by 4 different codons.

Examine the picture that shows a section of mRNA. Suppose a point mutation occurred which created an early "stop" codon (UAA, UAG, or UGA) so that the amino acid chain making the protein was stopped too soon. Which of the 7 codons shown was changed to "stop"?

A. Codon 2
Incorrect. It would take 2 changes to make UAG from Codon 2. A point mutation is just 1 change.

B. Codon 3
Correct! G must have changed to U to make UAG.

C. Codon 4
Incorrect. It would take 3 changes to make a “stop” codon from Codon 4.

D. Codon 5
Incorrect. It would take 2 changes to make a “stop” codon from Codon 5.

Examine the following change in DNA:

Evaluate the significance of the change, using the mRNA codon chart below. According to your evaluation, which of the following statements is true?

A. Even though the DNA sequence changed, no amino acids were changed.
Incorrect. Two new amino acids were formed.

B. The new DNA sequence caused 1 amino acid change, but it is not significant since it takes many changes in amino acids to have an effect on the protein.
Incorrect. It is possible for even one amino acid change to alter the structure of a protein.

C. The new DNA sequence caused a change in RNA transcribed, causing 2 new amino acids to form and potentially changing the protein.
Correct! By using the codon chart you can see that the new amino acids are PHE and PRO.

D. The new DNA sequence caused a new RNA sequence that caused one amino acid to be changed.
Incorrect. Two amino acids were changed.

A mutation was found in which the DNA sequence changed from CCCGGGAGA to CCCAGA. What kind of mutation is this?

A. Deletion
Correct! GGG has been deleted.

B. Frame-shift
Incorrect. In a frame-shift mutation, regrouping of 3 letter codons starts in a different place, for instance CCCGGGAGA might become CCGGGA.

C. Inversion
Incorrect. In an inversion, sequences of letters are reversed.

D. Insertion
Incorrect. In an insertion, at least one extra letter is inserted.