Ch. 18 Concept Check & Comprehension Questions

Question 1

A mutation that changes a codon into a stop codon is a ___ ___.

Answer 1

Nonsense mutation

Question 2

A down promoter mutation causes the promoter of a gene to be ___ like the consensus sequence and ___ transcription.

Answer 2

Less, inhibits

Question 3

A mutation in one gene that reverses the phenotypic effects of a mutation in a different gene is..

Answer 3

An intergenic suppressor

Question 4

Which of the following is an example of a somatic mutation?

Answer 4

• a mutation in an embryonic muscle cell

- a mutation in an adult nerve cell

Question 5

In the replica-plating experiments of the Lederbergs, bacterial colonies appeared at the same locations in each of two secondary plates because..

Answer 5

The mutations occurred on the master plate prior to T1 exposure and prior to replica plating.

Question 6

Which of the following is NOT an example of a spontaneous mutation?

Answer 6

A mutation caused by UV light

Question 7

A point mutation is caused by ..

Answer 7

• depurination
• deamination
• tautomeric shift

Question 8

One way that TNRE may occur involves the formation of ___ that disrupts ___.

Answer 8

A hairpin, DNA replication

Question 9

Nitrous acid replaces amino groups with keto groups, a process called ___.

Answer 9

Deamination ?

Question 10

A mutagen that is a base analog is..

Answer 10

5-bromouracil ?

Question 11

In the Ames test, ___ number of colonies is observed if a substance ___ a mutagen, compared with the control that is not exposed to the suspected mutagen.

Answer 11

Significantly higher, is not ?

Question 12

The function of photolyase is to repair..

Answer 12

Thymine dimers

Question 13

Which of the following DNA repair systems may involve the removal of a segment of a DNA strand?

Answer 13

• base excision repair
• nucleotide excision repair
• mismatch repair

Question 14

In nucleotide excision repair in E. coli, the function of the UvrA/UvrB complex is to..

Answer 14

Detect DNA damage

Question 15

Double-strand breaks can be repaired by..

Answer 15

• homologous recombination repair (HRR)

- nonhomologous end joining (NHEJ)

Question 16

An advantage of translesion DNA polymerases is they can replicate ___, but a disadvantage is they ___.

Answer 16

Over damaged DNA, have low fidelity

Question 17

Cause of position effects.

Explain what the term position effect means.

Answer 17

Position effect means that the expression of a gene has been altered due to a change in its position along a chromosome.

Question 18

A position effect that alters eye color in Drosophilia.

Has the DNA sequence of the eye color gene been changed in part (b) compared with part (a)? How do we explain the phenotypic difference?

Answer 18

In part (b), the sequence of the eye color gene is not changed. The change in expression is due to a position effect.

Question 19

Example of a somatic mutation.

Can this trait be passed to offspring?

Answer 19

A somatic mutation is not passed from parent to offspring.

Question 20

Spontaneous depurination.

When DNA replication occurs over an apurinic site, what is the probability that a mutation will occur?

Answer 20

The probability is 75%.

Question 21

Spontaneous deamination of cytosine and 5-methylcytosine.

Which of these two changes is more difficult for DNA repair enzymes to fix correctly? Explain why.

Answer 21

The deamination of methylcytosine is more difficult to repair because thymine is a normal base found in DNA. This makes it difficult for DNA repair enzymes to distinguish between the correct and altered strand.

Question 22

Oxidation of guanine to 8-oxoguanine by a reactive oxygen species (ROS).

What is a reactive oxygen species?

Answer 22

A reactive oxygen species is a chemical that contains oxygen and may react with cellular molecules in a way that may cause harm.

Question 23

Base pairing of 5-bromouracil and it’s ability to cause mutation.

Does 5-bromouracil cause a transition or a transversion?

Answer 23

5-bromouracil causes a transition

Question 24

Formation and structure of a thymine dimer.

In people, what is a common cause of thymine dimer formation and in what cell type(s) would it be most likely to occur?

Answer 24

Thymine dimer formation is often the result of exposure to UV light. It most commonly occurs in skin cells.

Question 25

The Ames test for mutagenicity.

What is the purpose of the rat liver extract in this procedure?

Answer 25

Enzymes within the rat liver extract may convert non-mutagenic molecules into a mutagenic form. Adding the extract allows researchers to identify molecules that may be mutagenic in people.

Question 26

Direct repair of damaged bases in DNA.

Which of these repair systems is particularly valuable to plants?

Answer 26

Photolyase is particularly valuable to plants, which are exposed to sun and susceptible to thymine dimer formation.

Question 27

Nucleotide excision repair in E. coli.

Explain why cuts are made on both sides of the DNA damage.

Answer 27

Cuts are made on both sides of the DNA damage so the region can be removed by UvrD.

Question 28

Mismatch repair in E. coli.

Which of these three proteins is responsible for ensuring that the mismatched base in the newly made daughter strand is the one that is removed?

Answer 28

MutH distinguishes between the parental strand and the newly made daughter strand, which ensures that the daughter strand is repaired.

Question 29

DNA repair of a double-strand break via nonhomologous end joining.

What is an advantage and a disadvantage of this repair system?

Answer 29

An advantage of this DNA repair system is that it can occur at any stage of the cell cycle. A disadvantage is that it may be imprecise and result in a short deletion in the DNA.