ch7

Question 1

True or false: gene mutations may be spontaneous or induced

Answer 1

True

Question 2

Are gene mutations always silent?

Answer 2

No, they can be detrimental

Question 3

What is the rate of mutations

Answer 3

10^-7 to 10^-11 per base pair per round of replication. This is very low which is a good thing

Question 4

What are the major types of mutation

Answer 4

1. Point mutations
2. Frame shift mutations
3. Conditional mutations
4. Suppressor mutations

Question 5

How many base pairs are involved with point mutations

Answer 5

1 or a few (look at page 1 ch.7 notes if this doesnt make sense

Question 6

Explain frame shift mutations

Answer 6

Insertion or deletion of base pairs resulting in alternate codon usage

Question 7

True or false: frame shift mutations often result in intercalating agents

Answer 7

true

Question 8

Define intercalating agents

Answer 8

planar, aromatic molecules that can insert between the base pairs of DNA

Question 9

How do intercalating agents result in frame shift mutations

Answer 9

They push them apart slightly and cause more then one nucleotide to be inserted during replication

Question 10

Can very large insertions of deletions only a result of intercalating agents

Answer 10

no, very large insertions or deletions may also result from chromosomal breakage and repair

Question 11

Explain conditional mutations

Answer 11

mutants whose altered phenotype is only expressed under certain conditions

• most commonly used with temperature sensitive phenotypes
• usually in genes which would result in lethal effects if they were always inactive

Question 12

Explain how temperature sensitive phenotypes exhibit conditional mutations

Answer 12

• The cells grow at low temperatures without a noticeable different phenotype
• when moved to high temperature, the mutant phenotype is expressed

Question 13

Explain suppressor mutations

Answer 13

A mutation which has two mutations, one of which compensates for the presence of the other to generate a normal phenotype overall
-Commonly occurs in multi-enzyme complexes

Question 14

True or false: some chemical mutagens have very specific results

Answer 14

True

Question 15

Explain base analogs as a type of chemical mutagen

Answer 15

• i.e. 5 bromouracil can be inserted into DNA in the place of thymine
• This results in the occasional change of AT->GC base pairs as 5-bromouracil can base pair with A and G

Question 16

Explain monofunctional alkylating agents as a type of chemical mutagen

Answer 16

Ethyl methane sulphonate methylates G then the methylates G can pair with T

Question 17

Explain bifunctional alkylating agents as a type of chemical mutagen

Answer 17

• Nitrogen mustards, mitomycin nitrosoguanidine cross links the DNA strands together
• This cross link must be excised before transcription or replication can occur
• faulty excision leads to insertions and deletions

Question 18

How does Radiation act as a mutagen

Answer 18

• Bases of DNA strongly absorb UV light
• Lethal effect of UV light is due to the induction of the formation of pyrimidine dimers
• These dimers block replication and transcription

Question 19

What must be done when dimers form and block replication

Answer 19

• repairs must be made
• This area is excised starting 8 nucleotides up on the 5’ side and 4 nucleotides down on the 3’ side
• DNA polymerase I carries out the repair synthesis
• Nicks in the DNA backbone are sealed by DNA ligase

Question 20

True or False: If the level of damage caused by radiation causing mutations is reasonably low the repair is accurate and complete

Answer 20

True (DNA polymerase I proof reads as it makes the new strand

Question 21

What types of radiation are included in the ionizing radiation that causes mutations

Answer 21

x-rays and gamma rays

Question 22

Why does ionizing radiation cause damage

Answer 22

By ionizing water and other cellular components and generating free radicals

Question 23

True or False: Ionizing radiation can penetrate glass and tissues

Answer 23

True

Question 24

True or False: ionizing radiation is not used as a plant and animal mutagen

Answer 24

False

Question 25

True or False: ionizing radiation can react with and inactivate macromolecules

Answer 25

True

• DNA inactivation can lead to permanent effects due to gene dosage
• Can cause breaks in DNA backbone
• This breakage can lead to loss of pieces

Question 26

Explain SOS responses in regards to DNA damage

Answer 26

-If there is a high degree of damage to DNA, then repair mechanisms can lead to mutations

Question 27

What does high levels of DNA damage cause (SOS response)

Answer 27

The activation of many different repair systems, some of which are template independant

Question 28

What are most genes involved in the SOS response repressed by

Answer 28

the presence of the LexA protein

Question 29

What happens to LexA once repairs are complete in the SOS response

Answer 29

RecA protease function ceases and the LexA binds to the promoter regions of the repair genes to shit down the response