Ch 18 Gene Mutations & DNA Repair

Question 1

a heritable change in the DNA sequence of genetic information

Answer 1

mutation

Question 2

mutations that arise in somatic cells, which don’t produce gametes
mutation is passed on to all daughter cell, leading to clones

Answer 2

somatic mutations

Question 3

mutations that arise in germ-line cells, which produce gametes and can be passed on to future generations

Answer 3

germ-line mutations

Question 4

mutations that affect a single gene or locus
only detected by observing phenotypic effects

Answer 4

gene mutations

Question 5

mutations that affect number or structure of chromosomes
can be deserved directly

Answer 5

chromosome mutations

Question 6

alteration of a single nucleotide in the DNA

Answer 6

base substitution

Question 7

what is a transition base substitution?

Answer 7

a purine is replaced by a different purine; a pyrimidine is replaced by a different pyrimidine

Question 8

what is a transversion base substitution?

Answer 8

a purine is replaced by a pyrimidine; a pyrimidine is replaced by a different purine

Question 9

what is a transversion base substitution?

Answer 9

a purine is replaced by a pyrimidine; a pyrimidine is replaced by a different purine

Question 10

which arise more frequently? transitions or transversions? why?

Answer 10

transitions; easier to transform a base into its same type rather than a different one

Question 11

one or more nucleotides added into DNA sequence

Answer 11

insertion

Question 12

one or more nucleotides removed from DNA sequence

Answer 12

deletion

Question 13

mutations that result in changes in the reading frame of a gene

Answer 13

frame-shift mutations

Question 14

why do frameshift mutations generally have drastic effects on the phenotype?

Answer 14

frameshift mutations usually alter all amino acids encoded by the nucleotides following the mutation

Question 15

insertions/deletions that do not change the reading frame

Answer 15

in-frame insertions / in-frame deletions

Question 16

how do in-frame insertions/in-frame deletions arise?

Answer 16

insertions and deletions in multiples of 3 nucleotides leave the reading frame intact

Question 17

mutations where the number of copies of a set of trinucleotides increases

Answer 17

expanding trinucleotides repeats

Question 18

explain how expanding nucleotide repeats leads to anticipation

Answer 18

the more copies of the repeat present, the more likely the repeats will increase, and diseases caused by these expanding repeats become more severe in each generation

Question 19

what trinucleotide sequence is most often present in most diseases caused by expanding trinucleotide repeats

Answer 19

CNG

Question 20

explain how strand slippage can cause expansion of nucleotide repeats

Answer 20

During replication, DNA strands separate and begin replication. During replication, a hairpin may form on the newly synthesized strand, causing the sequence to be replicated twice, increasing the number of repeats on the new strand. In another round of replication of the new strand, the new DNA molecule contains addition copies of the repeated nucleotides

Question 21

mutation that alters the wild-type phenotype

Answer 21

forward mutation

Question 22

mutation that changes mutant back to wild-type phenotype

Answer 22

reverse mutation

Question 23

mutation that results in a different amino acid in the protein

Answer 23

missense mutation

Question 24

mutation that changes a sense codon into a stop codon, terminating translation

Answer 24

nonsense mutation

Question 25

mutation that doesn't change the amino acid sequence

Answer 25

silent mutation

Question 26

missense mutation that alters the amino acid sequence of a protein but does not change its function

Answer 26

neutral mutation

Question 27

mutation that causes the complete or partial absence of normal protein function

Answer 27

loss-of-function mutation

Question 28

mutation that causes the cell to produce protein or gene product with a new function

Answer 28

gain-of-function mutation

Question 29

mutations expressed only under certain conditions

Answer 29

conditional mutations

Question 30

mutations that cause premature death

Answer 30

lethal mutations

Question 31

mutation that hides the effect of another mutation at a nucleotide distinct from the original mutation site

Answer 31

suppressor mutation

Question 32

explain how suppressor mutations are different than reverse mutations

Answer 32

suppressor mutations occur at a site different from the site of the original mutation, whereas a reverse mutation changes the mutated site back back to its original wild-type

Question 33

suppressor mutation that takes place within the same gene that contains the mutation being suppressed

Answer 33

intragenic suppressor mutation

Question 34

explain how intragenic suppressor mutations occur (three ways)

Answer 34

-suppressor may change a second nucleotide at a different site in the same gene to restore the original amino acid -suppressor may suppress a frameshift mutations, by inserting or deleting a nucleotide -making compensatory changes in the protein

Question 35

suppressor mutation that occurs in a gene different than the one with the original mutation that it suppresses

Answer 35

intergenic suppressor mutation

Question 36

explain how an intergenic suppressor mutation can occur

Answer 36

a second mutation that encodes for a tRNA that is capable of pairing with the original mutation's codon

Question 37

the frequency with which a wild-type allele changes to a mutant allele

Answer 37

mutation rate

Question 38

list the three factors that affect mutation rates

Answer 38

1. frequency that a mutation takes place 2. probability a mutation is repaired 3. probability mutation is detected

Question 39

mutations that arise from natural changes in DNA or replication errors

Answer 39

spontaneous mutations

Question 40

mutations that are caused by environmental agents, like chemicals or radiation

Answer 40

induced mutations

Question 41

explain how strand slippage causes a deletion

Answer 41

template strand of DNA loops out, resulting in a nucleotide being omitted on the newly synthesized strand

Question 42

explain how strand slippage causes an insertion

Answer 42

the newly synthesized strand loops out, resulting in an extra nucleotide being synthesized in the next round of replication

Question 43

explain how unequal crossing over causes insertions and deletions

Answer 43

when homologous chromosomes misalign, they crossover, and one chromosome has an insertion where the other has a deletion

Question 44

the loss of a purine base from a nucleotide

Answer 44

depurination

Question 45

how does depurination occur? what is produced?

Answer 45

the covalent bond connecting a purine to the 1' carbon atom of deoxyribose breaks, producing an apurinic site

Question 46

a nucleotide that lacks its purine base

Answer 46

apurinic site

Question 47

what results from the presence of an apurinic site

Answer 47

since the apurinic site cannot act as a template for a complementary base during replication, an incorrect nucleotide (usually adenine) is incorporated in the new DNA strand

Question 48

a base substitution causes a mispaired base to be incorporated into a newly synthesized nucleotide chain

Answer 48

incorporated error

Question 49

the loss of an amino group from a base

Answer 49

deamination

Question 50

what results from deamination?

Answer 50

deamination can alter the pairing properties of a base, causing it to pair with a different nucleotide than it's supposed to

Question 51

what occurs from the deamination of cytosine?

Answer 51

cytosine is turned into uracil, which then pairs with adenine instead of a C*G pair, a U*A pair forms, which replicates into T*A

Question 52

any environmental agent that significantly increases the rate of mutation above the spontaneous rate

Answer 52

mutagen

Question 53

chemicals with structures similar to those of any of the four standard nitrogenous bases of DNA and can be incorporated into new DNA

Answer 53

base analogs

Question 54

explain how base analogs can cause mutations

Answer 54

base analogs can be incorporated into new DNA, instead of the standard base. the base analog may pair with the original complementary base, but it may also pair with a different base, causing a mutation

Question 55

molecules similar to the size of nucleotides that can sandwich themselves between adjacent bases in DNA

Answer 55

intercalating agents

Question 56

what are the effects of intercalating agents?

Answer 56

by intercalating between bases in DNA, the 3D DNA helix is distorted, causing insertions and deletions, thus producing frameshift mutations

Question 57

what are the effects of ionizing radiation from X-rays, gamma rays, cosmic rays, etc

Answer 57

they dislodge electrons from atoms, changing them into free radicals and reactive ions, which then alter structures of bases and break phosphodiester bonds, and frequently cause double-strand breaks in DNA

Question 58

what is the effect if UV light

Answer 58

UV light has less energy, and pyrimidines absorb UV light, resulting in the creation of pyrimidine dimers

Question 59

how do pyrimidine dimers form?

Answer 59

pyrimidines absorb UV light, causing chemical bond to form between two adjacent pyrimidines on the same DNA strand, which distorts the normal DNA configuration, often blocking replication

Question 60

DNA sequences that are capable of moving around in the genome

Answer 60

transposable elements (transposons_

Question 61

how can transposable elements cause mutations?

Answer 61

transposons insert themselves into a gene and disrupt it; or promote chromosome rearrangements

Question 62

what are the general characteristics of transposable elements (two of them)

Answer 62

short flanking direct repeats terminal inverted repeats

Question 63

what are flanking direct repeats? how are they associated with transposons? how do they arise?

Answer 63

flanking direct repeats are short, directly repeated sequences (~3-12 bp) present on both sides of the transposon they are not a part of the transposon staggered cuts made in target DNA produced short single-stranded pieces of DNA on either side of transposon. replication of these ends produces the flanking direct repeats

Question 64

what are terminal inverted repeats and how are they associated with transposons?

Answer 64

terminal inverted repeats are sequences at both ends of a transposon that are inverted complements of one another

Question 65

why are terminal inverted repeats required for transposition?

Answer 65

enzymes catalyzing transposition recognize these sequences in order to locate the transposon

Question 66

movement of a transposable element from one location to another

Answer 66

transposition

Question 67

what are the three steps of transposition?

Answer 67

1. staggered breaks made in target DNA 2. transposable element joined to single-stranded ends of target DNA 3. DNA is replicated at single-stranded gaps

Question 68

enzyme that makes single-stranded breaks in DNA during transposition, and is often encoded by the transposon

Answer 68

transposase

Question 69

transposable elements that transpose as DNA

Answer 69

DNA transposons

Question 70

transposable elements that transpose through an RNA intermediate

Answer 70

retrotransposons

Question 71

how does a retrotransposon move?

Answer 71

a transposable element (DNA) is transcribed into RNA, which is then copied back into DNA by reverse transcriptase

Question 72

new copy of transposable element moves to a new site while the original transposable element remains at its old site, therefore increasing the number of transposon copies

Answer 72

replicative transposition

Question 73

transposable element is excised from its original site and inserted into a new site, therefore no increase in transposon copies

Answer 73

nonreplicative transposition

Question 74

describe mismatch pair

Answer 74

incorrectly paired bases and small unpaired loops in DNA are detected and corrected by mismatch-repair enzymes mismatch-repair enzymes used original DNA strand as template to correct the error

Question 75

how do mismatch-repair enzymes distinguish between the old and new strands of DNA (in bacteria)

Answer 75

old strands contain methyl groups (on the adenine nucleotides)

Question 76

describe direct repair

Answer 76

modified bases are restored back into their original (correct) structures

Question 77

describe base-excision repair

Answer 77

a modified base is excised, then the entire nucleotide is replaced

Question 78

describe nucleotide-excision repair

Answer 78

bulky lesions that distort the DNA double helix are removed, and any other DNA damage