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Genetics > G1 > Flashcards

G1 Flashcards

1
Q

what is a silent mutation

and a synonomous mutation

A

triplet encodes the same AA

syn = codon specifies different but functionally equivalent

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2
Q

what could mutation in intron cause

A

including in exon,

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3
Q

what could mutation in promoter cause

A

over/under expression

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4
Q

what are the 3 mechanisms that mutagens act through?

A

replacing a base
altering a base
damaging a base

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5
Q

what kind of mutagens induce base replacement

A

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

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6
Q

what is tautomeric shift

A

base present in one of several forms (isomers)

taumeric shift is the sponatenous isomerisation of a nitrogen base to an alternative hydrogen bonding form

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7
Q

what is the normal tautomeric form in DNA bases

A

keto form

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8
Q

what happens if you get imino form of cytosine

A

pairs with adenine

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9
Q

what happens if ou get imino for of adenine

A

pairs with cytosine

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10
Q

what happens if you get the enol form of thymine

A

pairs with guanine

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11
Q

what happens if you get the enol for of guanine

A

pairs with thymine

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12
Q

what is 5- bromo uracil

A

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

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13
Q

what does 5-bromouracil do in dna

A

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

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14
Q

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

A

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

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15
Q

what type of organism does nitrous acid work best in

A

prokaryotes

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16
Q

what do alkylating agents do

A

cause specific mispairing

17
Q

what type of organism do alkylating agenets work best in

A

both pro and euk works well

18
Q

what are two common alkylating agents

A

EMS and NMG

ethylmethanesulfonate and nitrosoguanidine

19
Q

what is the most mutagenic wavelength of UV

A

254nm

20
Q

what does UV light do to DNA

- what are the knock on effects of this

A

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
Q

What is human xeroderma pigmetosum

A

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

22
Q

What is the SOS system in E.coli

A

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

23
Q

describe the SOS system in E.coli

A

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
Q

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

A

yeast

25
Q

What are the most common types of radiation

A

Gamma rays
cobalt 60
or xrays

26
Q

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

A

directly proportional to the dose recieved

27
Q

shorter the wavelength of radiation=

A

higher the energy and penetrating power

28
Q

what does ionizing radiation cause?

A

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
Q

what are the most prevelent resulting mutations from radiation

A

thhymine glycol

8-oxo-7-hydrodeoxyguanosine

30
Q

what are intercalating agents

A

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

31
Q

what effect do intercalating agents have on DNA

A

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
Q

what is the Ames test for mutagenicty

A

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
Q

what are the two most likely photoproducts from UV light?

A

cyclobutane pyrimidine photodimer

6-4- photoproducts

Genetics (22 decks)

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