Chapter 7:DNA Mutation, DNA repair and Transposable Elements

Question 1

Chromosomal mutations?

Answer 1

changes involving whole chromosomes

Question 2

Point Mutations?

Answer 2

a change of one or a few base pairs. It may change the phenotype of the organism if it occurs within the coding region of a gene or in the sequences regulating the gene.

Question 3

Gene mutations?

Answer 3

mutations which affect the function of genes. It can alter the phenotype by changing the function of a protein.

Question 4

Mutation??

Answer 4

the process by which the sequence of base pairs in a DNA molecule is altered. It may result in a change to either a DNA base pair or a chromosome

Question 5

A cell with a mutation is called what?

Answer 5

a mutant cell

Question 6

There are two classifications of mutations based on the type of cell they occur in, what are they?

Answer 6

Somatic mutation and germ-line mutation

Question 7

Somatic mutation?

Answer 7

• mutation happening in a somatic cell
• the mutant characteristic affects only the individual in which the mutation occurs is not passed on to the succeeding generation.

Question 8

Germ-line mutation?

Answer 8

• a mutation in the germ line of sexually reproducing organisms
• may be transmitted by the gametes to the next generation producing an individual with the mutation in both its somatic and germ line cells.

Question 9

Mutation rate?

Answer 9

the probability go a particular kind of mutation as a function of time

ex: # of mutations per nucleotide pair per generation
ex: number per gene per generation

Question 10

Mutation frequency?

Answer 10

the number of occurrences of a particular kind of mutation

Question 11

What are the two types of point mutations?

Answer 11

1. Base pair substitutions

2. Base pair insertions or deletions

Question 12

Base pair substitutions??

Answer 12

change from one base pair to another in DNA

Question 13

What are the two general types of Base Pair substitutions?

Answer 13

1. Transition mutation

2. Transversion mutation

Question 14

Transition mutation???

Answer 14

a mutation from one purine-pyrimidine base pair to the other purine-pyrimidine base pair.
(A-T to G-C)

Question 15

Transversion mutation??

Answer 15

a mutation form purine-pyrimidine base pair to a pyrimidine-purine base pair.
( G-C to C-G)

Question 16

Where do point mutations USUALLY occur. Is that a good thing?

Answer 16

• noncoding region

- yes …bad if in coding region obv

Question 17

Base pair substitutions in protein coding genes are also defined in terms of their effects on aa sequences in proteins. What are the four types of mutation effects?

Answer 17

1. Missense Mutation
2. Nonsense Mutation
3. Neutral Mutation
4. Silent Mutation

Question 18

Missense Mutation??

Answer 18

• a gene mutation in which a base pair change causes a change in the mRNA codon so that a different aa is inserted into the polypeptide. A phenotypic change is noted.

Question 19

What is an example of a Missense mutation in regards to a genetic disease?

Answer 19

• Sickle cell anemia…….usually it codes for glutamic acid but the mutation codes for valine and results in a phenotypic change in the resulting protein functionality.

Question 20

Nonsense mutation???

Answer 20

a gene mutation in which a base pair change alters an mRNA codon for an aa to a stop (nonsense) codon ( UAG, UAA or UGA)
- causes premature terminating of polypeptide chain synthesis.
- it will be transcribed but translation is where the issue is.
L> Non-functional polypeptide is result.

Question 21

Example of a nonsense mutation from lecture?

Answer 21

LGR-4 (RARE NONSENSE MUTATION)
L> low bone mineral density and osteoporosis fractures. Electrolyte imbalance, low testosterone, increased risk of squamous cancer carcinoma

Question 22

Neutral Mutation??

Answer 22

• a base pair change in a gene that changes a codon in the mRNA such that the resulting aa produces no detectable change in the FUNCTION of the protein translated from that message.
  L>the mutated aa has similar properties to the original aa or the aa that was mutated has no significant importance tot he polypeptide.
  L> no phenotypic change
• there is a chance they may benefit from this mutation such that there is an advantage in the changed aa

Question 23

Example of a Neutral Mutation from lecture??

Answer 23

• APO-AIM more effective at removing cholesterol, helps prevent oxidation. There was an original arginine substituted by cysteine, improving HDL.
  L> discovered in a tiny city in Italy.

Question 24

Silent Mutation??

Answer 24

• aka synonymous mutation
• a mutation that changes a base pair in agent but the altered codon in the mRNA specifies the SAME aa in the protein
• often occurs by changes such as at the third wobble position of a codon.

Question 25

What type of mutation effect do base pair deletions or insertions have?

Answer 25

• frameshift mutation

Question 26

Frameshift mutation??

Answer 26

• an addition or deletion of one base pair shifts the mRNA’s downstream reading frame by one base pair so that incorrect aa’s are added to the polypeptide after the mutation site.

Question 27

Effects of a frameshift?

Answer 27

• may generate new stop codons
• result in longer than normal proteins
• result in significant alterations in aa sequence (primary structure) of a polypeptide.

Question 28

A frameshift mutation is produced by the insertion or deletion of any number of base pairs in the DNA that is not divisible by ?

Answer 28

three

Question 29

Example of a frameshift mutation from lecture?

Answer 29

-Gaucher’s disease- insertion base pair of DNA prevents production of enzymes that normally real down glycolipids. Enlarged liver, spine, fractured bones and neurological impairment.

Question 30

What is a forward mutation?

Answer 30

• changes a wilde type(common one in pop) gene to a mutant gene.

Question 31

What is a reverse mutation? (back mutation)

Answer 31

• changes a mutant gene at the same site so that it functions in a completely wild type or nearly wild type way.

Question 32

What are the two types of reverse mutations?

Answer 32

1. True reversion

2. Partial reversion

Question 33

True reversion mutation?

Answer 33

• reversion is back to the wild type aa

Question 34

Partial reversion mutation?

Answer 34

• reversion is to some other aa…and complete or partial function may be restored depending on the change.

Question 35

Partial reversion is generally due to a what?

Answer 35

second point mutation in the same gene; in coding region….3 positions you can have a mutation

• if one is mutated, you can have other mutations in another lace in the codon..not impossible to get the same mutation at the same site.
• intragenic (within gene) suppression: second mutation in the same gene can mask the first mutation.

Question 36

Supressor mutations??

Answer 36

• a mutation at a different site from that of the original mutation. A suppressor mutation masks or compensates for the effects of the initial mutation, but it does NOT REVERSE the original mutation

Question 37

Two types of suppressor mutations?

Answer 37

1. Intragenic supression

2. Intergenic supression

Question 38

Intragenic suppressors?

Answer 38

• mutation occurs within the same gene where the original mutations occurred but at a different site.

Question 39

Intergenic suppressors?

Answer 39

• mutation occurs in a different gene

Question 40

How do intragenic suppressors work?

Answer 40

• altering a different nucleotide in the same codon where the original mutation occurred or by altering a nucleotide in a different codon/

Question 41

How do intergenic suppressors work?

Answer 41

• a second mutation in another gene

- genes that cause the suppression of mutations in other genes= suppressor genes

Question 42

Since intergenic suppressors are the result of a second mutation in another gene …how do they effect the gene that has the mutation with which it effects?

Answer 42

• change the way in which the mRNA is red by tRNA

L> only suppresses the effects of one type of mutation

Question 43

Intergenic suppression (non sense suppresors) are divided into three classes what are they?

Answer 43

• one class of tRNA adds a substitute for UAA
• one class adds a fake substitute aa for UAG
• one suppresses AUG

Question 44

A gene for a tRNA changes the way it reads a mRNA and consequently it does what?

Answer 44

• adds its own aa in versus following the stop codon.