LECTURE 1 (The molecular basis of mutation 1) Flashcards
(42 cards)
What is a mutation?
Change in DNA seq of a gene
How can a mutation be passed to future generations? (uni and multicelular)
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.
Are mutations always bad?
No! Think of genetic variation and of mutations being the main source of evolutionary change.
What are point mutations?
The change of a single base pair.
What are the two main point mutations at the DNA level?
transitions (PuxPu, PyrxPyr) and transversions (PuxPyr)
Name the point mutations at protein level. (4)
- 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
What are indels?
Can be frameshift, insertion, deletion of nucleotides if it’s not 3 the whole protein sequence might change
What happens if there is a mutation at the intron level?
If the intron is spliced then it won’t affect the phenotype
What are mutagens? Which types of mutagens are there?
They’re agents inducing mutations. we can find: physical, chemical, biological
Mutagents act through 3 mechanisms, which ones?
- replacing a base
- altering a base
- damaging a base
What are base analogs? (6 characteristics)
- 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.
What is tautomeric shift?
The mispairing result from the change of one tautomer into another.
Which is the most common base replacement analog mutagen?
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)
What are isomers ?
compounds composed with the same number of elements but arranged differently
What are tautomers?
Tautomers are constitutional isomers of organic compounds that readily interconvert by a chemical reaction called tautomerization.
two mutagens inducing base alterations.
- 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
What is EMS?
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)
At which wavelength does UV light cause cancer in humans?
254nm
What type of mutagen is UV light?
It induces base damage by producing dimers between pyrimidines so kinks occur and nothing can pair; this gives a pre-mutational lesion.
All organisms on Earth are struggle for…
survival.
What are the two types of dimers that we can encounter due to UV light?
- cyclobutane pyrimidine photodimer
- 6-4 photoproducts (occuring bt C6 and C4 of pyrimidines)
What is the SOS system in bacteria?
It is a survival system that allows the tolerance of certain mutations
What are the genes UmuC and UmuD?
They are genes that participate in the SOS system and encode pol V. They can oversee an error in the DNA seq.
Describe the SOS system. Describe the translesion DNA synthesis.
drawing.
