Chapter 18: Gene Mutations and DNA Repair

Question 1

What are the two forms of mutations?

Answer 1

Somatic mutations: occur in somatic cells, wont be transmitted to progeny
Germinal mutations: occur in germ-line cells and will be transmitted to progeny

Question 2

What are the base substitution mutations?

Answer 2

Single nucleotide change
Transition: Pyrimidine with another pyrimidine or purine for another purien
Transversion: Pyrimidine for purine or purine for pyrimidine

Question 3

What are purines and pyrimidines?

Answer 3

purines: A,G
pyrimidines: T,C,U

Question 4

What is a frameshift mutation?

Answer 4

insertions or deletions of one or two base pairs alter the reading frame

Question 5

What is a tautomeric shift mutation?

Answer 5

Movement of H atoms from one position in a purine or pyrimidine base to another, can generate rare A:C and G:T base pairs

Question 6

What is an expanding nucleotide repeat mutation?

Answer 6

expansion of the triplet repeats, loops are formed between bases that are complementary and then extra nucleotides are added because it cant recognize the loop

Question 7

What is the pattern of expanding nucleotide repeats and the severity of the mutation?

Answer 7

The greater the number of repeats, the earlier the onset of the disease

Question 8

What are the 10 effects of mutations?

Answer 8

1. forward - wt-> mutant
2. reverse - mutant->wt
3. missense - amino acid -> different amino acid
4. nonsense - sense codon -> nonsense codon (stop)
5. silent - codon -> synonymous codon (no change in aa but diff codon)
6. neutral - amino acid change with no observable change in protein function
7. loss of function mutation - cause complete/partial loss of protein function
8. gain of function mutation - causes cell to produce protein whos function is not normally present
9. coniditonal mutation - expressed under certain conditions
10. lethal - causes death

Question 9

What is a suppressor mutation?

Answer 9

second site mutation that hides or suppresses the effect of the first mutation (can be within the same gene or on different genes)

Question 10

Are mutations rare?

Answer 10

YES

Question 11

What are spontaneous vs induced mutations?

Answer 11

Spontaneous - occur from internal factors
Induced - occur from exposure to external factors

Question 12

Which mutation is more common, spontaneous or induced?

Answer 12

spontaneous

Question 13

What are the 5 spontaneous replication errors?

Answer 13

1. tautomeric shifts
2. mispairing due to other structures - arise through wobble effect or by protonated forms of certain bases
3. incorporated errors and replicated errors
4. causes of deletions and insertions
5. spontaneous chemical changes

Question 14

What is incorporated error and replicated errors?

Answer 14

can be caused by a tautomeric shift or by the wobble effect or wobble could replicate again to create normal base pairing except opposite (e.g. go from A:T to C:G)

Question 15

What are the causes of deletions and insertions?

Answer 15

strand slippage - one base loops out and extra is copied creating insertion or deletion
unequal crossing over during meiosis - one crossing over product contains insertion and the other a deletion

Question 16

What is depurination?

Answer 16

breakage of the covalent bond between the purine base and the 1’ carbon atom of the deoxyribose sugar, so random nt is added, usually an A

Question 17

What is deamination?

Answer 17

loss of an amino group, typically from cytosine, gives rise to uracil (End results is a C->T)

Question 18

What are the 7 classes of mutagens?

Answer 18

1. Base analogs
2. Alkylating Agents
3. Deaminating chemicals
4. Hydroxylamine
5. Oxidative Radicals
6. Intercalating Agents
7. Radiation

Question 19

What are Base analogs?

Answer 19

mutagen that are chemicals with structures similar to any of the 4 standard nucleotides and can cause a mispair

Question 20

What are alkylating agents?

Answer 20

mutagens that react with dna bases and add methyl or ethyl groups

Question 21

What is hydroxylamine?

Answer 21

mutagen that adds a hydroxyl group to cytosine (C->T)

Question 22

What are deaminating chemicals?

Answer 22

mutagen that creates addition to spontaneous deamination noted for spontaneous chemical changes

Question 23

What are oxidative radicals?

Answer 23

mutagens that are reactive forms of oxygen, can create new chemicals which can mispair with the wrong complementary base

Question 24

What are intercalating agents?

Answer 24

mutagens that sandwich themselves between adjacent base pairs and distorts the helix, they can cause insertions and deletions

Question 25

What is radiation?

Answer 25

mutagen:
Xrays - produce ionizing radiation, dislodge electrons from atoms, breaks phosphodiester bonds leading to double stranded breaks
UV - produce less ionizing radiation which induce chemical bonds between two adjacent pyrimidine molecules on same strand of dna

Question 26

What are two general features of dna repair?

Answer 26

1. most dna repair mechanisms require double stranded dna
2. dna repair has built in redundancy

Question 27

What are the 6 DNA repair mechanisms?

Answer 27

1. mismatch repair
2. direct repair
3. base-excision repair
4. nucleotide excision repair
5. repair of double stranded breaks
6. diseases related to faulty dna repair

Question 28

What is mismatch repair?

Answer 28

dna repair mech
methylation allows differentiation of good and mutated strand, nicks dna up until bad nucleotide and redo’s replication

Question 29

What is direct repair?

Answer 29

dna repair mech