Deck 17: Gene Mutations and DNA Repair

Question 1

Mutations are heritable changes in DNA. They are essential to the study of genetics and are useful in many other biological fields.
-How are mutations used to help in understanding basic biological processes?

Answer 1

Studying mutations that disrupt normal processes often leads to the identification of genes that normally play a role in the process and can help in understanding the molecular details of a process.

Question 2

Gene mutations consist of changes in a single gene and can be base substitutions (a single pair of nucleotides is altered) or insertions or deletions (nucleotides are added or removed). A base substitution can be a transition (substitution of like bases) or a transversion (substitution of unlike bases). Insertions and deletions often lead to a change in the reading frame of a gene.

-Which of the following changes is a transition base substitution?

A) Adenine is replaced by thymine.
B) Cytosine is replaced by adenine.
C) Guanine is replaced by adenine.
D) Three nucleotide pairs are inserted into DNA.

Answer 2

Guanine is replaced by adenine.

Question 3

A suppressor mutation overrides the effect of an earlier mutation at a different site. An intragenic suppressor mutation occurs within the same gene as that containing the original mutation, whereas an intergenic suppressor mutation occurs in a different gene.
-How is a suppressor mutation different from a reverse mutation?

Answer 3

A reverse mutation restores the original phenotype by changing the DNA sequence back to the wild-type sequence. A suppressor mutation restores the phenotype by causing an additional change in the DNA at a site that is different from that of the original mutation

Question 4

Mutation rate is the frequency with which a specific mutation arises. Rates of mutations are generally low and are affected by environmental and genetic factors.
-What three factors affect mutation rates?

Question 5

Spontaneous replication errors arise from altered base structures and from wobble base pairing. Small insertions and deletions can occur through strand slippage in replication and through unequal crossing over.
-How does an incorporated error differ from a replicated error?

Question 6

Chemicals can produce mutations by a number of mechanisms. Base analogs are inserted into DNA and frequently pair with the wrong base. Alkylating agents, deaminating chemicals, hydroxylamine, and oxidative radicals change the structure of DNA bases, thereby altering their pairing properties. Intercalating agents wedge between the bases and cause single-base insertions and deletions in replication.

-Base analogs are mutagenic because of which characteristic?

A) They produce changes in DNA polymerase that cause it to malfunction.
B) They distort the structure of DNA.
C) They are similar in structure to the normal bases.
D) They chemically modify the normal bases

Question 7

Mismatched bases and other DNA lesions are corrected by mismatch repair. Enzymes cut out a section of the newly synthesized strand of DNA and replace it with new nucleotides.

-Mismatch repair in E. coli distinguishes between old and new strands of DNA on the basis of

A) differences in base composition of the two strands.
B) modification of histone proteins.
C) base analogs on the new strand.
D) methyl groups on the old stran

Question 8

Direct-repair mechanisms change altered nucleotides back into their correct structures. In base-excision repair, glycosylase enzymes recognize and remove specific types of modified bases. The entire nucleotide is then removed and a section of the polynucleotide strand is replaced.
-How do direct-repair mechanisms differ from mismatch repair and base-excision repair?

Question 9

Defects in DNA repair are the underlying cause of several genetic diseases. Many of these diseases are characterized by a predisposition to cancer.
-Why are defects in DNA repair often associated with increases in cancer?