9.11.1 Genetic Mutation

Question 1

note

Answer 1

• Genetic mutations result from defects in the chromosomes or changes in the normally occurring DNA sequence. A point mutation is a change in a single nucleotide pair in a gene.
• In a normally functioning cell, the processes of transcription and translation ensure a specific sequence of amino acids.
An error in the amino-acid sequence can change the protein’s structure and function.
• In humans, a single point mutation in the gene coding for hemoglobin can cause sickle-cell anemia.
- Sickle-cell anemia is a disease caused by a defect in the protein hemoglobin. The defect results in abnormal red blood cells that have a sickled shape (as shown to the left). Sickle-cell anemia occurs in 1/400 African Americans and is caused by a point mutation, a change of a single nucleotide within a gene.
- Sickle-cell anemia is caused by the substitution of a single amino acid in the hemoglobin protein. This substitution is the result of a change in a single nucleotide in the hemoglobin gene. As shown in the diagram to the left, the mutant hemoglobin gene has a thymine (T) replaced by an adenine (A). This alteration results in the substitution of the amino acid valine in place of a glutamic acid in the polypeptide chain.
- Glutamic acid has a polar R group and is hydrophilic.
Therefore, it is attracted to other amino acids. Valine,
however, has a nonpolar R group, and it will position itself towards the middle of the folded polypeptide chain to minimize contact with the aqueous environment. The
abnormally shaped hemoglobin that results will crystallize when the oxygen content in the blood gets low and cause red blood cells to sickle.

Question 2

An example of a type of genetic mutation is

Answer 2

• inversion.
• deletion.
• translocation.

Question 3

How can some point mutations in coding regions have no effect on the amino acid sequence that is formed?

Answer 3

• Several different nucleotide sequences can code for the same amino acid.

Question 4

Which of the following statements is TRUE?

Answer 4

• If one nucleotide in a codon is changed a point mutation will result.

Question 5

How does a point mutation affect the protein that is coded for by a gene?

Answer 5

• A point mutation can cause a different amino acid to be coded for, changing the structure of a particular protein.

Question 6

Which statement below describes a point mutation?

Answer 6

• A change in a single nucleotide in a gene

Question 7

Why do most point mutations in humans have no effect on phenotype?

Answer 7

• Most point mutations occur in portions of the DNA that do not code for proteins.

Question 8

The disease sickle cell anemia occurs when the amino acid __________ replaces the normally occurring amino acid __________.

Answer 8

• valine, glutamic acid