Lecture 8 Notes

Question 1

Molecular mechanism of recombination

Answer 1

• DNA is cut
• an exonuclease produces single-stranded regions with exposed 3’ ends
• strand invasion results in heteroduplex formation
• formation of a double Holliday junction
• branch migration extends the region of heteroduplex
• resolution of the Holliday Junctions

Question 2

gene conversion from recombination

Answer 2

heteroduplexes formed during recombination may have different sequences (alleles) on the two DNA strands of a single DNA

Question 3

mutations

Answer 3

change in base pair sequence of DNA

Question 4

substitution

Answer 4

changing one nucleotide for another

Question 5

deletion

Answer 5

deleting a nucleotide from a sequence

Question 6

insertion

Answer 6

inserting a nucleotide into the sequence

Question 7

slipped mispairing

Answer 7

DNA polymerase pauses and newly synthesized strand slips

Question 8

triplet repeat diseases - polyQ

Answer 8

Q= amino acid glutamine
protein is altered
dominant mutant
ex: Huntington disease

Question 9

non poly Q triplet repeat diseases

Answer 9

ex: fragile x syndrome
no alteration of protein structure
alteration of mRNA 5’ UTR interferes with protein expression

Question 10

triplet repeats

Answer 10

have hyper mutability

Question 11

mutagens

Answer 11

things in the environments that can cause mutations

Question 12

somatic mutations

Answer 12

mutations that occur in body cells (aren’t passed down0

Question 13

germ line mutations

Answer 13

mutations that occur in sex cells and can be passed down

Question 14

point mutations

Answer 14

can produce or revert a mutant

Question 15

forward mutation

Answer 15

wild type -> mutant

test: screening

Question 16

reverse mutation

Answer 16

mutant -> wild type

test: selection

Question 17

the rate of forward mutation is always higher than for reverse mutation. How can you explain this?

Answer 17

there are many stages for forward mutation but only one target for reverse mutation

Question 18

how to determine mutagens?

Answer 18

the Ames test

Question 19

ways to grow bacteria

Answer 19

• plates of colonies

- suspension

Question 20

auxotrophs

Answer 20

mutants that cannot complete a biosynthetic pathway

-cannot grow on minimal medium without a supplement

Question 21

screening

Answer 21

• forward mutation

- complete medium and then replicas: one minimal medium and one minimal medium + supplement

Question 22

selection

Answer 22

• reverse mutation

- minimal medium

Question 23

alkylating agents

Answer 23

add ethyl or methyl groups

Question 24

intercalating agents

Answer 24

• enhances slippage replication mistakes

- planar structure similar to many dyes