Ch 12- DNA Mutation And Repair

Question 1

Mutation

Answer 1

A change in a DNA sequence that is propagated through cellular generations

Question 2

Point mutation

Answer 2

A mutation consisting of a single base pair change

Question 3

2 categories of point mutations:

Answer 3

1) transitions

2) transversions

Question 4

Transition mutation

Answer 4

Exchange of a purine-pyrimidine add pair for the other purine-pyrimidine base pair
ie: C-G becomes T-A or T-A becomes C-G

Question 5

Transversion mutation

Answer 5

Replacement of a purine-pyrmidine Base pair with a pyrimidine-purine base pair or vice versa
Ie: C-G becomes either G-C or A-T

Question 6

Which are more frequent transitions or transversions?

Answer 6

Transitions

Question 7

Which are more harmful transitions or transversions?

Answer 7

Transversions

Question 8

Classifications of point mutations:

Answer 8

• silent
• missense
• nonsense

Question 9

Silent mutation

Answer 9

Is a nucleotide change that produces a codon for the same amino acid

Ex: GAA & GAG both code for glutamate

Question 10

Missense mutation

Answer 10

A nucleotide changes the residues to a different amino acid

Ex: glutamate(GAA) -> glutamine (CAA)

Question 11

Nonsense mutation

Answer 11

Changes nucleotide sequence so that instead of encoding on amino acid, the triplet functions as a stop codon, terminating translation process and generating a truncated protein w/o a complete amino acid sequence

Question 12

Oncogenes

Answer 12

Encode proteins that drive the cell cycle forward

Question 13

Tumor suppressor genes

Answer 13

Encode proteins that suppress cell division

-many are transcription factors that regulate expansion of genes that drive the cell cycle

Question 14

Indels

Answer 14

• insertions

- deletions

Question 15

Insertion deletion

Answer 15

Occur when one or more base pairs are added to the wild type sequence

Question 16

Deletion mutation

Answer 16

Are due to the loss of one or more base pairs

Question 17

What causes indels?

Answer 17

Recombination or template slippage by DNA pol during replication

Question 18

Reading frame

Answer 18

The DNA sequence from the start codon to the stop codon

Question 19

Frameshift mutation

Answer 19

An indel mutation of only 1 or 2 base pairs in the coding sequence of a protein changes the reading frame

Question 20

Indels that occur in multiples of 3 no preserve reading frame of the gene, contain repeats, and retain some function. T or F?

Answer 20

True

Question 21

Triplet repeat diseases

Answer 21

Disease caused by the insertion of triplet sequences

Question 22

Polyglutamine (polyQ) diseases

Answer 22

<50% of triplet expansions involve codon CAG which is for gluayamine (Q)

Question 23

Mutations that usually cannot be repaired:

Answer 23

• duplication
• inversion
• translocation

Question 24

Duplication mutation

Answer 24

Amplification of a large tract of DNA, leading to increased dense dosage effects

Question 25

Inversion mutation

Answer 25

Result from the large section of DNA in a chromosome and can have varied effects

Question 26

Translocation mutation

Answer 26

Occurs when two nonhomologous chromosomes exchange large regions of DNA

Question 27

Dreamination

Answer 27

The removal of an amino group from a compound, and all molecules that contain an amino group are possible targets of hydrolytic attack

Question 28

Abasic site

Answer 28

A position in an intact DNA backbone that is w/o a base

Question 29

Depurination

Answer 29

Hydrolysis of N-beta glycosyl bond in purines

Question 30

Alkylation

Answer 30

The addition of an alkyl group to atoms in nucleotide bases or to the phosphodiester backbone

Question 31

Carcinogen

Answer 31

Any substance directly involved in promoting cancer

Question 32

Genotoxic

Answer 32

Cause chemical changes to genomic DNA

Question 33

Cytotoxic

Answer 33

Can kill cell, used in cancer treatments

Question 34

Mismatch repair system (MMR)

Answer 34

An enzymatic system for repairing base mismatches (non-Watson crick base pairs) in DNA

• almost always corrected to reflect parental strand
• can also recognize up to 4 bp of unpaired nucleotides formed by template slippage

Question 35

Base excision repair (BER)

Answer 35

A DNA repair pathway that involves excision of a damaged base by DNA glycosylase, followed by cleavage of the DNA backbone adjacent to the site by an AP endonuclease. Nick translation, DNA polymerization, and ligation complete the repair.

Question 36

Nucleotide excision repair (NER)

Answer 36

A DNA repair pathway that involves exinuclease-catalyzed cleavage of the phosphodiester bond on either side of a bulky DNA lesion such as a pyrmidine diner or base adduct, followed by removal of the segment containing the lesion, then DNA polymerization and ligation to fill the gap

Question 37

Transcription coupled repair (TCR)

Answer 37

A nucleotide excision repair pathway in eukaryotes that is triggered when RNA polymerase encounters a lesion in the DNA and stalls

Question 38

Translesion synthesis (TLS)

Answer 38

A pathway for replicating DNA across lesions that occur in unwound DNA at the replication fork. The pathway uses a TLS polymerase that lacks a proofreading exonuclease and has a less-selective active site. Although this polymerase may introduce a mutation, it allows replication to proceed.

Question 39

What are the ways in which dna pol might make a mistake during replication?

Answer 39

• incorporate a tautomeric base
• miss a mismatch
• pol without exonuclease activity
• template slippage
• recombination

Question 40

Why are there multiple glycosylases utilized during BER?

Answer 40

Detects the uracil sand it will fall in AP endonuclease and this removes a base (uracil) and “knicks” the DNA backbone, adds cytosine instead of uracil, then DNA pol I synthesizes

Question 41

What type of damage is sustained when cells are subjected to UV, gamma and X-rays?

Answer 41

UV- thymine dimer

X ray- single stranded and double stranded break