Question 1

Planar molecules used as chemical mutagens are called

Accepted Answer

Intercalating agents are planar molecules that insert themselves between DNA base pairs, causing frameshift mutations during DNA replication.

Question 2

Chemical mutagens that mimic the naturally occurring bases are called

Accepted Answer

Chemical mutagens that mimic the naturally occurring bases are called base analogs. Nitrogen mustards and alkylating agents are chemical mutagens that directly modify DNA. Nitrous oxide is a gas that can induce mutations in bacteria, but it is not specifically a base analog. Therefore, the best choice is C.

Question 3

Irradiation of cells with ultraviolet light may cause

Accepted Answer

Irradiation of cells with ultraviolet light can cause thymine dimers, where adjacent thymine bases in a strand of DNA become covalently linked, leading to distorted DNA structure and potentially causing mutations. The other options are not associated with the effects of UV light on DNA.

Question 4

Which is not true about mismatch repair?

Accepted Answer

Mismatch repair does not remove both strands in the mismatch area. Instead, it selectively removes the incorrect base from the newly synthesized strand and replaces it with the correct base.

Question 5

Thymine dimers are dealt with by

Accepted Answer

Thymine dimers are formed when two adjacent thymine bases are covalently linked by a UV radiation-induced cyclobutane ring. These dimers can be repaired by two mechanisms: photoreactivation repair, which requires the enzyme photolyase and can only be used in the presence of visible light, and excision repair, which removes the affected bases and replaces them with new ones. Therefore, the best choice is E, as both photoreactivation repair and excision repair can deal with thymine dimers.

Question 6

Chemical mutagens often act by altering the

Accepted Answer

Chemical mutagens often alter the hydrogen bonding properties of nucleobases, leading to mispairing during DNA replication and resulting in mutations.

Question 7

X-rays

Accepted Answer

X-rays cause ionization of molecules, which can lead to single and double-strand breaks in DNA molecules. These breaks can have serious consequences for cellular function and potentially lead to cancer or other adverse health effects. While X-rays do not typically make DNA radioactive, they can cause enough damage to the DNA to create mutations or other changes that can have long-lasting effects. Thymine trimers are more commonly associated with ultraviolet (UV) radiation, rather than X-rays.

Question 8

Segments of DNA capable of moving from one area in the DNA to another are called

Accepted Answer

Segments of DNA capable of moving from one area in the DNA to another are called transposons. The other options, base analogs, intercalating agents, and inverted repeats, do not refer to segments of DNA capable of moving from one area to another.

Question 9

The formation of a covalent bond between two adjacent thymines is caused by

Accepted Answer

UV radiation is known to cause the formation of covalent bonds between adjacent thymine bases in DNA, leading to the formation of thymine dimers. This can result in genetic mutations and increase the risk of cancer. Mustard gas and alkylating agents can also damage DNA but do not specifically cause thymine dimers. Microwave radiation is not known to cause DNA damage.

Question 10

The source of variation among microorganisms that were once identical is

Accepted Answer

The source of variation among microorganisms that were once identical is mutation. Mutations, which are changes in the DNA sequence, can lead to changes in the phenotype and can result in new traits that may confer a selective advantage, like antibiotic resistance or increased virulence. Virulence factors and sigma factors may be affected by mutations but are not the source of variation.

Question 11

The characteristics displayed by an organism in any given environment is its

Accepted Answer

The phenotype is the physical and behavioral characteristics displayed by an organism in a given environment. It is determined by the interaction between the organism's genotype and environmental factors. Therefore, D is the correct answer. A, B, and C are not correct since they do not accurately describe an organism's physical or behavioral characteristics.

Question 12

The designation his^- refers to

Accepted Answer

The answer of The designation his^- refers to ...

Question 13

Antibiotics

Accepted Answer

Antibiotics can create a selective pressure that favors the growth of preexisting mutants that are already resistant to the antibiotic. This can lead to the evolution of antibiotic-resistant bacterial populations. Antibiotics do not directly cause mutations or increase the rate of spontaneous mutation, and they do not act as alkylating mutagens.

Question 14

The largest group of chemical mutagens consists of

Accepted Answer

The largest group of chemical mutagens consists of alkylating agents, which include chemicals like ethylmethanesulfonate, nitrosoguanidine, and dimethylsulfate. These agents add alkyl groups to the nitrogenous bases of DNA, causing structural changes that can lead to mutations. Radiation is another type of mutagen, but it does not fall under the category of chemical mutagens. Base analogs and nitrous acid are also chemical mutagens, but they do not make up the largest group.

Question 15

Transposons

Accepted Answer

All of the choices are correct. Transposons are known as jumping genes because they can move or transpose themselves within the genome. This movement can cause insertion mutations, where the transposon inserts itself into a new location within the DNA sequence, potentially disrupting a gene's function. In some cases, transposons can also cause knockout mutations, where the disrupted gene is no longer functional. Transposons were first recognized in plants, but they are found in a wide range of organisms, including bacteria, fungi, and animals.

Question 16

Which change in a gene's DNA sequence would have the least effect on the eventual amino acid sequence produced from it?

Accepted Answer

Addition or deletion of three nucleotides will only cause a frameshift mutation if it is not a multiple of three. However, if it is triplet code, the codon reading frame will shift but the same amino acid sequence can be preserved. This type of mutation is called a silent mutation, which is the least disruptive type of mutation. Therefore, the addition or deletion of three consecutive nucleotides would have the least effect on the eventual amino acid sequence produced from it.

Question 17

Intercalating agents

Accepted Answer

Intercalating agents are molecules that can insert themselves between the two adjacent base pairs of DNA. They exert their effect during DNA synthesis and can cause frameshift mutations by interfering with the normal separation of DNA strands during replication. Therefore, choice E is the best option as it includes both correct statements. The other choices are incorrect as intercalating agents do not only act in dormant cells and do not alter the hydrogen bonding properties of the bases.

Question 18

On which of the following DNA strands would UV radiation have the most effect?

Accepted Answer

UV radiation primarily causes damage by forming thymine dimers, which occur between adjacent thymine bases on a DNA strand. The strand "AATTAGTTC" has the most thymine bases, making it more susceptible to UV-induced damage.

Question 19

The properties of a cell that are determined by its DNA composition are its

Accepted Answer

The answer of The properties of a cell that are...

Question 20

DNA repair mechanisms occur

Accepted Answer

DNA repair mechanisms occur in both eukaryotes and prokaryotes. These mechanisms are essential for maintaining the integrity of the genetic material, and they help to prevent mutations and preserve the function of the genome. Different types of DNA damage can be repaired by different mechanisms, including direct reversal, base excision repair, nucleotide excision repair, and double-strand break repair. These mechanisms are present in all living organisms, from bacteria to humans, and are critical for ensuring the survival and adaptation of cells to changing environments.

Quiz 8: Bacterial Genetics