Topic 8-1

Question 1

two thymine bases covalently bind and block DNA replication

Answer 1

pyrimidine dimer

Question 2

system allows bacterial cells to bypass the replication block with a mutation prone pathway

Answer 2

SOS system in bacteria

Question 3

in eukaryotes, the pyrimidine dimer is replaced by AA

Answer 3

DNA polymerase eta

Question 4

what are the main types of DNA repair mechanisms for pyrimidine dimers?

Answer 4

• SOS system in bacteria
• DNA pol. eta in eukaryotes

Question 5

high energy radiation (x-rays, gamma rays) remove electrons from atoms, altering the chemical structure of bases and inducing:

Answer 5

double stranded DNA breaks

Question 6

UV radiation causes the formation of:

Answer 6

pyrimidine dimers (usually TT, but can be TC/CC)

Question 7

list the six main types of chemically induced mutations:

Answer 7

• base analogs
• alkylating agents
• deamination
• hydroxylamine
• oxidative reactions
• intercalating agents

Question 8

resembles thymine, except that it has a bromine atom in place of a methyl group on the 5C atom

Answer 8

5-bromouracil

Question 9

a chemically induced mutation where the chemical strucutre of a molecule resembles a nucleotide base

Answer 9

base analogs

Question 10

a chemically induced mutation where molecules add an alkyl group to normal nucleotides

Answer 10

alkylating agents

Question 11

________ converts guanine into 8-oxy-7,8-dihydrodeoxyguanine

Answer 11

oxidative radicals

Question 12

molecules such as proflavin, acridine orange, etc, insert themselves between adjacent bases in DNA, distorting the 3D structure of the helix - can also cause insertions and deletions which results in frameshift mutations

Answer 12

intercalating agents

Question 13

how do we test chemicals to identify mutagens?

Answer 13

the Ames test is used to identify chemical mutagens

Question 14

uses his- strains of bacteria to test chemicals for their ability to produce his-/his+ mutations

Answer 14

the Ames test

Question 15

what are forward genetic screens?

Answer 15

identify genes that contribute to a phenotype/trait. after conducting a genetic screen, we have a collection of new mutations

Question 16

what are the two main problems with forward genetic screens?

Answer 16

1) we don’t know if some of the same genes have been hit multiple times
2) in a genetic screen, one mutant strain may have more than one mutated gene

Question 17

are crucial for the identification of new mutants

Answer 17

complementation tests

Question 18

what is the purpose of a complementation test?

Answer 18

to determine whether two mutations are alleles of the same gene

Question 19

‘parasitic’ DNA sequences that can move about the genome

Answer 19

transposable elements

Question 20

movement of the transposons. may take place through a DNA or RNA intermediate.

Answer 20

transposition

Question 21

what are the features of transposition?

Answer 21

• flanking direct repeats
• terminal inverted repeats

Question 22

a type of transposition where a new copy of the transposable elecment inserts in a new location, and the old copy stays behind (copy and paste)

Answer 22

replicative transpostition

Question 23

a type of transposition where the old copy excises from the old site and moves to a new site (cut and paste)

Answer 23

nonreplicative transposition

Question 24

a type of transposition which requires reverse transcription to integrate into the target site (PDF –> copy to word doc –> print to PDF)

Answer 24

RNA intermediate transposition

Question 25

in humans, about _____% of the human genome comprises sequences that are related to transposable elements, mostly _______

Answer 25

45%, retrotransposons

Question 26

transposons cause mutations by:

Answer 26

• inserting into another gene
• promoting chromosomal rearrangements
• deleting and inserting genes as they move

Question 27

IS1

Answer 27

simple transposable elements found in bacteria

Question 28

Tn10

Answer 28

a composite transposon in bacteria

Question 29

who was the first person to discover transposable elements?

Answer 29

Barbara McClintock

Question 30

Ac and Ds

Answer 30

transposable elements in maize.