Lecture--Chapter 18

Question 1

Gene mutations have both good and bad aspects. What are they?

Answer 1

1. They allow variation in gene alleles and are essential for evolutionary change.
2. Most mutations are harmful.

Question 2

a group of processes by which a cell identifies and corrects damage to its DNA

Answer 2

DNA repair

Question 3

Human cells have approximately how many molecular lesions per cell every day?

Answer 3

~1 million

Question 4

relatively small changes in DNA sequence

Answer 4

gene mutations

Question 5

What are the different types of gene mutations?

Answer 5

1. Base substitutions
2. Deletions or additions of one or more basepair
3. Spontaneous or induced biochemical changes

Question 6

What are the different types of base substitutions?

Answer 6

1. point mutations
2. transition mutations
3. transversion mutations

Question 7

a change in a single basepair

Answer 7

point mutation

Question 8

a change of one purine (pyrimidine) to another purine (pyrimidine)

Answer 8

transition mutation

Question 9

exchange of a purine and a pyrimidine

Answer 9

transversion mutation

Question 10

A silent base substitution has how many amino acids altered and what is the likely effect on protein function?

Answer 10

none; none

Question 11

A missense base substitution has how many amino acids altered and what is the likely effect on protein function?

Answer 11

one; neutral or inhibitory

Question 12

A nonsense base substitution has how many amino acids altered and what is the likely effect on protein function?

Answer 12

many; inhibitory

Question 13

A frameshift addition or deletion has how many amino acids altered and what is the likely effect on protein function?

Answer 13

many; inhibitory

Question 14

a hereditary blood disorder for homozygotes, characterised by RBCs that have an abnormal, rigid, sickle shape

Answer 14

sickle cell disease

Question 15

Heterozygotes for sickle cell disease have some protection against which disease?

Answer 15

malaria

Question 16

Gene mutation of the promoter sequence may have what effect?

Answer 16

May increase or decrease the rate of transcription.

Question 17

Gene mutation of the regulatory element/operator site sequence may have what effect?

Answer 17

May disrupt the ability of the gene to be properly regulated.

Question 18

Gene mutation of the 5’-UTR/3’-UTR sequence may have what effect?

Answer 18

May alter the ability of mRNA to be translated; may alter mRNA stability.

Question 19

Gene mutation of the splice recognition sequence may have what effect?

Answer 19

May alter the ability of pre-mRNA to be properly spliced.

Question 20

Mutation effects at the genotype level:

Answer 20

1. Wildtype (WT) allele
2. Mutant allele
3. Revertant allele

Question 21

Mutation effects at the phenotype level:

Answer 21

1. Deleterious mutation
2. Lethal allele
3. Beneficial allele
4. Conditional mutants
5. Suppressor mutations

Question 22

a relatively prevalent allele in a population

Answer 22

wildtype (WT) allele

Question 23

derived from a WT allele, relatively rare occurrence

Answer 23

mutant allele

Question 24

a mutant allele changed back to a WT allele

Answer 24

revertant allele

Question 25

decreases chance of survival and reproduction

Answer 25

deleterious mutation

Question 26

results in death of the organism

Answer 26

lethal allele

Question 27

improves individual survival and reproduction

Answer 27

beneficial allele

Question 28

the phenotype is apparent under limited situations

Answer 28

conditional mutants

Question 29

second site mutations that convert the mutant phenotype to a WT phenotype

Answer 29

suppressor mutations

Question 30

Examples of suppressor mutations:

Answer 30

1. intragenic 2. intergenic (redundant function) 3. intergenic (common pathway)

Question 31

A 1st mutation disrupts normal protein function. A suppressor mutation in the same protein restores function. This is known as:

Answer 31

intragenic

Question 32

A 2nd mutation alters a different protein to carry out that function. (gain of new enzyme function) This is known as:

Answer 32

intergenic (redundant function)

Question 33

A 2nd mutation in a downstream pathway protein may compensate for a defect in an upstream pathway protein. This is known as:

Answer 33

intergenic (common pathway)

Question 34

changes in gene expression due to chromosomal rearrangements

Answer 34

position effects

Question 35

What are the two different movements of position effects?

Answer 35

1. Movement to a location influenced by new regulatory sequences. 2. Movement between euchromatic regions and heterochromatic regions.

Question 36

all progeny cells carry the change in DNA

Answer 36

germ-line mutation

Question 37

a non-heritable change in DNA

Answer 37

somatic mutation

Question 38

often occurs early in embryonic development or later from environmental mutagens

Answer 38

somatic mutation (genetic mosaic)

Question 39

an organism can pass on characteristics that it acquired during its lifetime to its offspring (Lamarck)

Answer 39

physiological adaptation hypothesis

Question 40

mutations occur in a non-purposeful fashion

Answer 40

random event hypothesis

Question 41

What are the different common spontaneous causes of mutations?

Answer 41

1. aberrant recombination 2. aberrant segregation 3. errors in DNA replication 4. transposable elements 5. depurination 6. deamination 7. tautomeric shifts 8. toxic metabolic products

Question 42

What are the different common induced causes of mutations?

Answer 42

1. chemical agents | 2. physical agents

Question 43

abnormal crossing over may cause deletions, duplications, translocations, and inversions

Answer 43

aberrant recombination

Question 44

abnormal chromosomal segregation may cause aneuploidy or polyploidy

Answer 44

aberrant segregation

Question 45

a mistake by DNA polymerase may cause a point mutation

Answer 45

errors in DNA replication

Question 46

can insert themselves into the sequence of a gene

Answer 46

transposable elements

Question 47

on rare occasions, the linkage between complementary purines and deoxyribose can spontaneously break. If not repairs, it can lead to a mutation

Answer 47

depurination

Question 48

cytosine and 5-methylcytosine can spontaneously create uracil or thymine

Answer 48

deamination

Question 49

spontaneous changes in base structure can cause mutations if they occur immediately prior to DNA replication

Answer 49

tautomeric shifts

Question 50

the products of normal metabolic processes, such as reactive oxygen species, may be chemically reactive agents that can alter the structure of DNA

Answer 50

toxic metabolic products

Question 51

chemical substances may cause changes in the structure of DNA

Answer 51

chemical agents

Question 52

physical phenomena such as UV light and X-rays can damage the DNA

Answer 52

physical agents

Question 53

a deamination that is generally fixed by excision repair

Answer 53

cytosine deamination

Question 54

a deamination that is not readily repaired

Answer 54

methylcytosine deamination

Question 55

Bisulfite (HSO3-) induced cytosine deamination is used in _____.

Answer 55

DNA sequencing

Question 56

isomers of molecules that readily interconvert by the migration of a hydrogen atom, with a switch of a single bond and an adjacent double bond

Answer 56

tautomers

Question 57

Tautomeric shifts can cause ____.

Answer 57

mutations

Question 58

Tautomeric shift mismatches often are repaired by ______ or _______.

Answer 58

1. DNA proofreading activity | 2. a mismatch repair system

Question 59

deaminates C to U and A to hypoxanthine, which alters base pairing during DNA replication

Answer 59

nitrous acid (HNO2)

Question 60

formed readily from sodium nitrate (HNO3-)

Answer 60

nitrous acid (HNO2)

Question 61

a mutagenic and possibly carcinogenic organic compound

Answer 61

ethyl methanesulfonate (EMS)

Question 62

produces random mutations in genetic material by nucleotide subsitution, which typically results in point mutations (GC to AT):

Answer 62

ethyl methanesulfonate (EMS)

Question 63

What are the steps of the common treatment to obtain plant mutants?

Answer 63

1. Soak seeds in EMS for about 1 day. 2. Grow your plants 3. Isolate DNA 4. Do a PCR and sequencing screen

Question 64

UV light is a non-ionising radiation that produces _____. It is the primary cause of _____.

Answer 64

thymine dimers; skin cancer

Question 65

skin cancer is repaired in some organisms by:

Answer 65

photoreactivation

Question 66

the likelihood that a given gene will be mutated

Answer 66

mutation rate

Question 67

Most people have how many mutations in their DNA during their life?

Answer 67

100-200

Question 68

What are the common types of DNA repair systems?

Answer 68

1. direct repair 2. base excision repair and nucleotide excision repair 3. mismatch repair 4. homologous recombination repair 5. nonhomologous end joining

Question 69

an enzyme recognises an incorrect alteration in DNA structure and directly converts it back to a correct structure

Answer 69

direct repair

Question 70

an abnormal base or nucleotide is first recognised and removed from the DNA, and a segment of DNA in this region is excised, and then the complementary DNA strand is used as a template to synthesis a normal DNA strand

Answer 70

base excision repair and nucleotide excision repair

Question 71

similar to excision repair except that the DNA defect is a base pair mismatch in the DNA, not an abnormal nucleotide, The mismatch is recognised, and a segment of DNA in this region is removed. The parental strand is used to synthesise a normal daughter strand of DNA

Answer 71

mismatch repair

Question 72

Occurs at double-strand breaks or when DNA damage causes a gap in synthesis during DNA replication. The strands of a normal sister chromatid are used to repair a damaged sister chromatid.

Answer 72

homologous recombination repair

Question 73

Occurs at double-strand breaks. The broken ends are recognised by proteins that keep the ends together; the broken ends are eventually rejoined.

Answer 73

nonhomologous end joining

Question 74

a light-dependent direct repair process

Answer 74

photoreactivation

Question 75

enzyme made by bacteria, fungi, most plants and some animals that cleaves thymine dimers

Answer 75

photolyase

Question 76

used by humans to fix thymine dimers

Answer 76

nucleotide excision repair

Question 77

also an in vitro technique to label DNA for hybridisation assays (DNAse, Pol I and labeled dNTPs, ligate)

Answer 77

nick translation

Question 78

recognises an abnormal base and cleaves the bond between the base and the sugar

Answer 78

N-glycosylase

Question 79

recognises a missing base and cleaves the DNA backbone on the 5' side of the missing base

Answer 79

AP endonuclease

Question 80

In E. coli, _____ uses its 5'--->3' exonuclease activity to remove the damaged region and then fills in the region with normal DNA. _____ seals the region.

Answer 80

DNA polymerase I; DNA ligase

Question 81

repair by direct ligation of chromosome ends without using a homologous template

Answer 81

non-homologous end joining