G1 Flashcards Preview

Genetics > G1 > Flashcards

Flashcards in G1 Deck (33):
1

what is a silent mutation
and a synonomous mutation

triplet encodes the same AA
syn = codon specifies different but functionally equivalent

2

what could mutation in intron cause

including in exon,

3

what could mutation in promoter cause

over/under expression

4

what are the 3 mechanisms that mutagens act through?

replacing a base
altering a base
damaging a base

5

what kind of mutagens induce base replacement

base analogue
chemical analogue of natural bases
incorperated into dna in place of normal base can cause errors in replication and high rate of tautomeric shift

6

what is tautomeric shift

base present in one of several forms (isomers)
taumeric shift is the sponatenous isomerisation of a nitrogen base to an alternative hydrogen bonding form

7

what is the normal tautomeric form in DNA bases

keto form

8

what happens if you get imino form of cytosine

pairs with adenine

9

what happens if ou get imino for of adenine

pairs with cytosine

10

what happens if you get the enol form of thymine

pairs with guanine

11

what happens if you get the enol for of guanine

pairs with thymine

12

what is 5- bromo uracil

in keto form is a thymine analogue contains bromine at C5 instead of CH3

13

what does 5-bromouracil do in dna

in keto form still pairs to adenine
however presence of bromine modifies electron distributtion of ring, can be enol form or ionised form
which pairs with guanine
= promotes transitions

14

what effect does nitrous acid (HNO2) have on the bases


promotes oxidative deamination converting NH2 amino groups to keto groups
cytosine ->uracil (pairs A)
Adenine -> hypoxanthine (pairs c)
Guanine -> Xanthine (pairs C)

15

what type of organism does nitrous acid work best in

prokaryotes

16

what do alkylating agents do

cause specific mispairing

17

what type of organism do alkylating agenets work best in

both pro and euk works well

18

what are two common alkylating agents

EMS and NMG
ethylmethanesulfonate and nitrosoguanidine

19

what is the most mutagenic wavelength of UV

254nm

20

what does UV light do to DNA
- what are the knock on effects of this

cause dimers between adjacent pyrimidines
TT or TC dimers distorting double helix and interfereing wiith replication
the wrong base can then be inserted opposite them causing a missense/nonsense mutations
= premutational lesion

21

What is human xeroderma pigmetosum

a autosomal recessive disease that is caused by a defect in excision repair of pyrimidine dimers

22

What is the SOS system in E.coli

last resort damage tolerance that allows cells to survive with a degree of mutagenesis

23

describe the SOS system in E.coli

UmuC or UmuD genes (which encode subunits of DNAPV)
code for error prone polymerases
DNAP3 stops at a non coding lesion (eg photodimer)
generating ss regions that attract Ssb protein and Rec A which form filaments
presence of RecA filaments signals cells to synthesize UmuD which is cleaved by RecA to yield UmuD adn UmuC
UmuC forms a complex with UmuD allowing DNAP to proceed past the lesion.

24

what eukaryotes have been found to code for error prone polymerases as in SOS

yeast

25

What are the most common types of radiation

Gamma rays
cobalt 60
or xrays

26

what does the number of mutations caused by ionizing radiation depend on?

directly proportional to the dose recieved

27

shorter the wavelength of radiation=

higher the energy and penetrating power

28

what does ionizing radiation cause?

a trail of ions giving rise to free radicals in tissues which made ss and ds breaks in DNA
reaction products are OH- O2-, H202 as 65% of body in water.

29

what are the most prevelent resulting mutations from radiation

thhymine glycol
8-oxo-7-hydrodeoxyguanosine

30

what are intercalating agents

acridine dyes such as proflavin and acridine orange= flat/planar molecules that mimic base pair and slips between stacked nitrogen bases and DNA

31

what effect do intercalating agents have on DNA

induce frameshit mutations leading to incorperation of an additional base on the opposite strand
as they increase spacing from 3-4A to 6A causing indel of bp at replication.

32

what is the Ames test for mutagenicty

uses bacteria to test whether a given chemical cna cause mutations in DNA
positive test = mutation
induces reversion of various his mutations in bacterium S.thyphimutium

33

what are the two most likely photoproducts from UV light?

cyclobutane pyrimidine photodimer
6-4- photoproducts