Chapter 18: Gene Mutations and DNA Repair

Question 1

Mutation

Answer 1

inheritable change in genetic information

Question 2

Where do somatic mutations occur?

Answer 2

nonreproductive cells

Question 3

How are somatic mutations passed?

Answer 3

through mitosis. clones of the cells are formed that have the mutant gene

Question 4

Where do germ line mutations occur?

Answer 4

in cells that give rise to gametes via meiosis and sexual reproduction

Question 5

What percentage of offspring will recieve the germ line mutation?

Answer 5

approximently half of the next generation

Question 6

Base substitution

Answer 6

alters a single codon

Question 7

What is a transition base substituition?

Answer 7

purine to purine or pyrimidine to pyrimidine

Question 8

What is a transversion base substitution?

Answer 8

purine to pyrimidine or pyrimidine to purine

Question 9

What gene mutation alters the reading frame and may change codons?

Answer 9

Base insertions/deletions

Question 10

What are indels caused by?

Answer 10

strand slippage and unequal crossing over

Question 11

What is a mutation that hides or supprots the effect of another mutation?

Answer 11

supressor mutation

Question 12

Where must supressor mutations occur?

Answer 12

at a site that is different than the site of the original mutation

Question 13

Where does an intragenic supressor mutation occur?

Answer 13

same gene

Question 14

Where does an intergenic supressor mutation occur?

Answer 14

different gene

Question 15

What type of mutation produces a new codon that encodes for a different amino acid?

Answer 15

missense mutation

Question 16

How does a missense mutation occur?

Answer 16

via changing the amino acid sequence

Question 17

What mutation produces a new codon that is a stop codon that prematurely terminates translation?

Answer 17

nonsense mutation

Question 18

What type of mutation produces a new codon that encodes the same amino acid?

Answer 18

silent mutation

Question 19

What type of mutation produces no change in amino acid sequence?

Answer 19

silent mutation

Question 20

What factors affect mutation rates?

Answer 20

-the frequency in which change takes place
-the probability that a mutation will be detected
-the repair rate

Question 21

What is a site that cannot provide a template for a complementary base on the newly synthesized strand?

Answer 21

apurinic site

Question 22

When do apurinic sites occur?

Answer 22

after base modifications and DNA glycosolases come in and degrade the base via base excision repair; leaving the spot without a base and available for later repair

Question 23

Depurination

Answer 23

loss of purine

Question 24

Deamination

Answer 24

loss of amino group

Question 25

Where do chemically induced mutations occur?

Answer 25

nitrogenous base

Question 26

What induces permenant change in a nitrogenous base?

Answer 26

mutagen

Question 27

What is a carcinogen?

Answer 27

controls mutation in cell division (cancer)

Question 28

What can be caused by base analogs?

Answer 28

point mutations

Question 29

What is the base analog of thymine and how does it occur?

Answer 29

5-bromouracil occurs due to mispairing

Question 30

Can DNA polymerase recognize 5-bromouracil?

Answer 30

yes because it is similar to thymine (causes mutations)

Question 31

What do alkylating agents do?

Answer 31

donate alkyl group

Question 32

Deamination produces....

Answer 32

nitrous acid

Question 33

What does hydroxylamine add?

Answer 33

hydroxyl group

Question 34

Intercalating agents produce...

Answer 34

ethidium bromide

Question 35

What does radiation increase in all organisims?

Answer 35

mutation rates

Question 36

What is a pyrimidine dimer?

Answer 36

two thymine bases that block replication

Question 37

Spontaneous mutations occur when

Answer 37

DNA polymerase makes a mistake

Question 38

What are the steps that lead to mispairing?

Answer 38

-DNA strands separate for replicaton -Thymine on the original template strand base pairs with guanine through wobble, leading to incorporated error -Next round of replication, the G pairs with C leading to a transition mutation

Question 39

How do you detect mutations with the Ames Test?

Answer 39

-Bacterial his- strains are mixed with liver enzymes (which have the ability to convert compounds into potential mutagens) \ -Some of the bacterial strains are also mixed with the chemical to be tested for mutagenic activity -The bacteria are then plated on medium that lacks histidine -Bacterial colonies that appear on the plates have undergone a his- to a his+ mutation -Any chemical that significantly increases the number of colonies on the treatment plate is mutagenic and therefore probably also carcinogenic

Question 40

What are sequences that can move about the genome?

Answer 40

transposable element

Question 41

What is transposition?

Answer 41

movement of the transposons>

Question 42

What do flanking direct repeats and terminal inverted repeats make up?

Answer 42

transposons

Question 43

How much of the genome do transposons make up?

Answer 43

~25%

Question 44

What makes staggered cuts in the DNA to create a transposon?

Answer 44

transposase

Question 45

What is transposase?

Answer 45

restriction enzyme that cuts in order for transposons to incorporate

Question 46

What is the key sign that something is a transposon?

Answer 46

replication of a single stranded DNA creates flanking repeats

Question 47

How do transposons cause mutations?

Answer 47

by inserting into another gene and promoting DNA rearrangement

Question 48

What makes up a composite transposon?

Answer 48

HAVE INSERTION SEQUENCES -almost always has a 9-bp flanking direct repeat -23 bp inverted repeat

Question 49

What is the transposes gene responsible for?

Answer 49

excision of transposon sequence

Question 50

What is the difference in composire and non-composite transposons?

Answer 50

there are no inverted repeat sequences in non-composite

Question 51

Where are non-composite transposons found?

Answer 51

bacteria

Question 52

How do retrotransposons work?

Answer 52

use reverse transcription to take RNA to DNA using reverse transcriptase

Question 53

What is the mechanisim of action for a transposon?

Answer 53

cut out and jump to a different part of DNA sequence

Question 54

How were transposons discovered?

Answer 54

through the studying of corn kernel phenotypes

Question 55

What is the mechanisim for mismatch repair?

Answer 55

methyhlation at the GATC sequences allows old and newly synthezised nucleotide strands to be differentiated

Question 56

What does a lag in methylation mean for mismatch repair?

Answer 56

the old strand will be methylated and the new strand will not due to the mismatched base

Question 57

How does direct repair work?

Answer 57

pyrimidine dimers can be reversed by photlyase

Question 58

What removes bases and produces apurinic sites in base excision repair?

Answer 58

DNA glycosolases

Question 59

What cleaves the phosphodiester bond in base excision repair?

Answer 59

AP endonucleases

Question 60

What end do AP endonucleases cleave on in base excision repair?

Answer 60

5' end

Question 61

Why is Nucleotide excision repair necessary?

Answer 61

damage to the DNA, distorts the configuration of the moleucle

Question 62

What recognizes the distortion that results from the damage?

Answer 62

an enzyme complex

Question 63

What is the function of single stranded binding proteins?

Answer 63

keeps DNA from coming back together

Question 64

Homologous recombination

Answer 64

repair joins double strands while repairing mistakes

Question 65

Nonhomologuous End Joining

Answer 65

repair joins double strands while introducing insertions and deletions

Question 66

What shows that NHEJ has occured?

Answer 66

inversions

Question 67

What are the symptoms of Xeroderma Pigmentosum?

Answer 67

freclelike spots on skin, sensitivity to sunlight, predisposition to skin cancer

Question 68

What is the genetic defect that causes xeroderma pigmentosum?

Answer 68

defects in nucleotide-excision repair (specifically in the UV light repair system)