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GENETICS > LECTURE 1 (The molecular basis of mutation 1) > Flashcards

LECTURE 1 (The molecular basis of mutation 1) Flashcards

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1
Q

What is a mutation?

A

Change in DNA seq of a gene

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2
Q

How can a mutation be passed to future generations? (uni and multicelular)

A

If it’s a unicelular organism, it’ll always be passed, if it’s multicellular it has to affect the germ line to be passed to future generations.

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3
Q

Are mutations always bad?

A

No! Think of genetic variation and of mutations being the main source of evolutionary change.

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4
Q

What are point mutations?

A

The change of a single base pair.

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5
Q

What are the two main point mutations at the DNA level?

A

transitions (PuxPu, PyrxPyr) and transversions (PuxPyr)

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6
Q

Name the point mutations at protein level. (4)

A
  • Silent mutation: encodes the same aa therefore no change in protein seq
  • synonymous mutaation: encodes a different aa but with similar properties.
  • Missense: encodes a different aa with different properties
  • Nonsense: encodes a premature stop codon
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7
Q

What are indels?

A

Can be frameshift, insertion, deletion of nucleotides if it’s not 3 the whole protein sequence might change

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8
Q

What happens if there is a mutation at the intron level?

A

If the intron is spliced then it won’t affect the phenotype

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9
Q

What are mutagens? Which types of mutagens are there?

A

They’re agents inducing mutations. we can find: physical, chemical, biological

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10
Q

Mutagents act through 3 mechanisms, which ones?

A
  • replacing a base
  • altering a base
  • damaging a base
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11
Q

What are base analogs? (6 characteristics)

A
  • they’re mutagens that induce base replacements.
  • They come from natural bases and they will replace a normal base.
  • They have several tautomers.
  • They’re not static
  • They have isomers as well.
  • We can find keto, imino and enol forms.
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12
Q

What is tautomeric shift?

A

The mispairing result from the change of one tautomer into another.

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13
Q

Which is the most common base replacement analog mutagen?

A

5-BU , in the keto form is a thymine analog. Instead of CH3 at C5 it has a bromine. This bromine can’t form a hydrogen bond. It normally pairs with adenine but in another isomer form it pairs with guanine. (this is a transition at the level of DNA)

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14
Q

What are isomers ?

A

compounds composed with the same number of elements but arranged differently

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15
Q

What are tautomers?

A

Tautomers are constitutional isomers of organic compounds that readily interconvert by a chemical reaction called tautomerization.

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16
Q

two mutagens inducing base alterations.

A
  • nitrous acid HN02: promotes oxidative deamination–> convert NH2 amino groups into leto groups (in prokaryotes) e.g adenine turns to hypoxanthine and pairs with cytosine
  • alkylating agents: works in prok and euk. causes specific mispairings, they’re lab mutagens e.g NG or EMS
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17
Q

What is EMS?

A

ethylmethanosulfate. it’s a base alteration mutagen that acts principally in G and T and adds ethyl or methyl groups (normally added at the O group)
e. g O-6-ethylguanine (which pairs with thymine)

18
Q

At which wavelength does UV light cause cancer in humans?

A

254nm

19
Q

What type of mutagen is UV light?

A

It induces base damage by producing dimers between pyrimidines so kinks occur and nothing can pair; this gives a pre-mutational lesion.

20
Q

All organisms on Earth are struggle for…

A

survival.

21
Q

What are the two types of dimers that we can encounter due to UV light?

A
  • cyclobutane pyrimidine photodimer

- 6-4 photoproducts (occuring bt C6 and C4 of pyrimidines)

22
Q

What is the SOS system in bacteria?

A

It is a survival system that allows the tolerance of certain mutations

23
Q

What are the genes UmuC and UmuD?

A

They are genes that participate in the SOS system and encode pol V. They can oversee an error in the DNA seq.

24
Q

Describe the SOS system. Describe the translesion DNA synthesis.

A

drawing.

25
Q

Adenine

A

draw

26
Q

Guanine

A

draw

27
Q

Thymine

A

draw

28
Q

Cytosine

A

draw

29
Q

What is the translesion DNA synthesis?

A

It’s analogous to the SOS system in bacteria but in eukaryotes, it’s a damage toleration mechanism.

30
Q

What is the name os the damage toleration mechanism in eukaryotes?

A

translesion DNA synthesis

31
Q

What are pol n and pol i for?

A

pol n: allows bypass of the lesion

pol i: introduces erroneous bases opposite the mutated sites.

32
Q

What does the excision repair mechanism have to do with mutations?

A

Repair enzymes can recognize a mutation in a base and they’ll cut a section of the DNA containing the base.

33
Q

Example of disease caused by error in excision repair mechanism.

A

Xenoderma pigmentosum.

34
Q

What is xenoderma pigmentosum?

A

It’s a disease that occurs due to UV light exposure. One gene becomes mutated and the excision repair mechanism doesn’t act properly therefore somatic mutations occurs leading to melanoma.

35
Q

What are the two main types of mutagens that cause base damage?

A

UV light and radiation (gamma rays, X-rays..)

36
Q

What are examples of radiation?

A

Gamma rays, X-rays, Cobalt 60… Can affect somatic or germ line cells.

37
Q

Characteristics of radiation.

A
  • The shorter the wavelength the higher the penetration
  • The higher the amount of radiation the more mutations
  • Free radicals cause ss and ds breaks in DNA
38
Q

How are free radicals produced?

A

By hydrolysis.

39
Q

repair of ss and ds breaks by free radicals.

A

ss- easy to repair

ds- diff to repair

40
Q

What is the highest damage radiation can cause? (2)

A

thymine glycol (stops replication) and 8-oxodG

41
Q

What are intercalating agents? example

A
  • other mutagens altering DNA
  • increases the spacing bt purines
  • they induce frame-shifts
  • they can revert mutations caused by themselves but not base substitutions.

e.g Ethidium bromide

42
Q

What is the ames test for?

A

test the mutagenicity of chemicals if there’s a positive response –> chemical is mutagenic

GENETICS (17 decks)

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