SAT II Biology M : Translation

Study concepts, example questions & explanations for SAT II Biology M

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Example Questions

Example Question #1 : Dna, Rna, And Proteins

What happens when one of the three codons of UAG, UAA, or UGA reach the A site on a ribosome that is helping facilitate translation?

Possible Answers:

Initiation 

Termination

Processing

Elongation

Propagation 

Correct answer:

Termination

Explanation:

UAG, UAA, and UGA are stop codons so when they enter the A site of a ribosome they will initiate the termination of translation.

Example Question #1 : Dna, Rna, And Proteins

Which of the following mutations is a single nucleotide base pair change that results in a codon for a different amino acid?

Possible Answers:

Missense mutation

Nonsense mutation

Insertion

Silent mutation

Deletion

Correct answer:

Missense mutation

Explanation:

A missense mutation is a type of point mutation (single base pair change) that alters the codon to the creation of a different protein.   

A silent mutation is also a point mutation with a change in one base pair, but with the resulting strand still coding for the same protein (hence the term "silent"). 

A nonsense mutation changes a codon from coding for an amino acid to coding for termination of the protein. The protein may or may not still be functional depending on how much of it is terminated when the mutation occurs.

An insertion is a mutation in which one or more base pairs is added to the coding sequence. Unless the insertion is in a multiple of three (preserving the frame because a codon is made up of three base pairs), it results in a "frame shift" that alters the reading frame of the codons to the right, causing it to code for a different set of proteins.

A deletion is another type of frame shift mutation, in which a base pair (or more) is deleted from the coding sequence, altering the reading frame to code for different proteins in many cases. As with insertions, if the deletion is in a multiple of 3, the frame is preserved as each codon consists of 3 base pairs.

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