Exam 4: Mutations and DNA replication/repair

Question 1

Depurination

Answer 1

bond between purine base and deoxyribose spontaneously hydrolyzes

Question 2

Deamination

Answer 2

Most common is conversion of cytosine to uracil

Question 3

Pyrimidine dimers

Answer 3

UV light causes dimerization of adjacent thymine bases on same DNA strand

Question 4

Somatic mutation

Answer 4

affects only cell where mutation occurred

Question 5

Germline mutation

Answer 5

mutation will be passed to offspring

Question 6

Gene mutations

Answer 6

variations in nucleotide sequence - affect only one gene

Question 7

Chromosomal mutations

Answer 7

rearrangements, deletions, or duplications of chromosomal regions

Question 8

Genomic mutations

Answer 8

addition or loss of chromosomes

Question 9

Mutations impacting chromatin

Answer 9

changes in methylation of DNA or in modification of histone proteins

Question 10

Point mutations

Answer 10

exchange of one nucleotide for another

Question 11

Silent mutation

Answer 11

mutation does not result in change in amino acid sequence

Question 12

missense mutation

Answer 12

change in sequence results in change in amino acid sequence

Question 13

nonsense mutation

Answer 13

change in nucleotide sequence results in a stop codon

Question 14

RNA processing mutant

Answer 14

change in nucleotide sequence destroys RNA splicing site or creates a new splicing site

Question 15

Small insertions and deletions are caused by

Answer 15

incorrect recombination (during meiosis - unequal crossover), strand slippage during replication, and intercalating agents

Question 16

nondisjunction

Answer 16

incomplete separation of chromosomes in meiosis; changes number of chromosomes in cell - genome mutation

Question 17

frequency of recombination between genes on same chromosomes is an

Answer 17

indicator of their proximity - shorter distance between genes = lower probability of crossover occurring

Question 18

Trisomy

Answer 18

extra copy of a chromosome present - observed for chromosomes 13, 18, and 21 only

Question 19

Monosomy

Answer 19

chromosome missing - if on an autosome it is lethal

Question 20

Mosaicism

Answer 20

some of individual composed of normal cells, whereas other parts contain mutations - somatic mutations that occur during embryogenesis (earlier it happens = more mutant cells)

Question 21

Strand-directed mismatch repair system

Answer 21

newly synthesized strand contains nicks that will be filled in later
Incorrectly paired bases cause distortion in DNA double helix - repair enzymes remove incorrect base pair and nucleotides to nearest nick - DNA polymerase fills in gap

Question 22

Lynch syndrome (hereditary nonpolyposis colorectal carcinoma HNPCC)

Answer 22

Heritable cancer - high change of developing colorectal cancer
Caused by defects in mismatch repair system

Question 23

DNA glycosylases

Answer 23

recognize specific types of altered base in DNA & catalyze their removal

Question 24

AP endonuclease

Answer 24

recognizes that a base is missing and cuts sugar-phosphate backbone on side of missing base

Question 25

DNA phosphodiesterase

Answer 25

removes deoxyribose phosphate group

Question 26

Nucleotide excision repair

Answer 26

repairs damage caused by agents that result in large changes in the structure of DNA, i.e. pyrimidine dimers
Uses helicase/nucleases to separate and cut strand; polymerase and ligase fills in gap

Question 27

xeroderma pigmentosum (XP)

Answer 27

Caused by mutations that abolish or impair function of proteins required for nucleotide excision repair
extreme sensitivity of skin to sunlight, pigmentation changes, and skin cancer

Question 28

Nonhomologous end-joining

Answer 28

broken DNA ends (when both strands break) are brought together and ligated - causes loss of nucleotide at breakpoint

Question 29

Homologous end-joining

Answer 29

recombination processes used to repair broken DNA without loss of information
Use other copy of chromosome to find sequence

Question 30

Cyatarabine

Answer 30

Used to treat acute leukemias
converted to cytarabine triphosphate inside cells - competes with deoxyribonucleotides to bind to DNA polymerases
DNA replication and repair blocked

Question 31

Cyclophosphamide

Answer 31

Used to treat Hodgkin’s lymphoma, lung, breast, and testicular cancers
Converted to phosphoramide mustard in liver - forms inter- and intra-strand DNA crosslinks, damage that blocks replication = cell death

Question 32

Doxorubicin

Answer 32

Used against a variety of tumors
forms a tripartite complex with DNA and topoisomerase II - interfers with catalytic cycle and prevents re-ligation of double stranded breaks = cell death