Chapter 8.1: The Genetic Code

Question 1

What are frameshift mutations?

Answer 1

 Changes that alter the grouping of nucleotides into codons are called frameshift mutations; they shift the reading frame for all codons beyond the point of insertions or deletion, almost always abolishing the function of the polypeptide product

Question 2

Define codon

Answer 2

o Each nucleotide triplet is called a codon

Question 3

What is evidence that a codon is composed of more than one nucleotide?

Answer 3

 Yanofsky observed that point mutations altering different nucleotide pairs may affect the same amino acid

Question 4

What is intragenic suppression?

Answer 4

 The restoration of gene function by one mutation cancelling another in the same gene is known as intragenic suppression

Question 5

Describe the non-template strand for mRNA (coding or noncoding’ sense or antisense)

Answer 5

 Other strand is the RNA-like strand, because it has the same polarity and sequence as the RNA
• Aka sense strand or coding strand

Question 6

What are nonsense mutations?

Answer 6

• Nonsense mutation changes a codon that signifies an amino acid (a sense codon) into one that does not (a nonsense codon)

Question 7

Describe the template strand for mRNA (coding or noncoding’ sense or antisense)

Answer 7

 One strand of DNA series as a template for the mRNA

• Known as template strand; antisense strand; non-coding strand

Question 8

What is a reading frame?

Answer 8

 Each gene has a starting point that establishes a reading frame: the sequential partitioning of nucleotides into groups of three to generate the correct order of amino acids in the resulting polypeptide chain

Question 9

What are missense mutations?

Answer 9

 Missense mutations change a codon for one amino acid into a codon that specifies a different amino acid

Question 10

The genetic code is degenerate. What does this mean?

Answer 10

 Genetic code is degenerate: two or more nucleotide triplets specify most of the 20 amino acids