Mutations Flashcards
what are bases
one of the molecular components of DNA
there are 5 types: Adenine, Guanine, Cytosine and Thymine (in DNA) or Uracil (in RNA)
what is a nucleoside
a component of nucleic acid consisting of a base linked to either a ribose or a deoxyribose molecule
what is a nucleotide
made of a base, a sugar and a phosphate group
what is a codon
a triplet of bases in the RNA to encode for an amino acid or a punctuation point in the synthesis of protein
what are mutations
any change in genetic information relative to a reference “wild-type” genome
what is a mutagen
any agent causing mutations
what is DNA polymerase
an enzyme catalyzing synthesis or breakdown of DNA
what is the mutation rate
probability of a particular kind of mutation as a function of time
what is the mutation frequency
number of occurrences of a particular kind of mutation
what are the types of mutations
point mutations
small insertions, deletions
gene duplications
major chromosomal change
examples of mutation sources
DNA polymerase errors during DNA replication
external effects - chemicals, radiation
failure of repair mechanisms
what is the importance of mutations
genes carry information needed for all of RNA and proteins in organism
survival and stability of each species depend on faithful replication of genetic information by each new generation
are mutations desired
low level of mutational change is highly desirable to provide the ability for species to adapt to changing environments
what mechanisms induce mutations
physical mutations - xrays - UV light chemical mutagens - base analogues - base modifying agents (alkylating agents, deaminating agents) - intercalating agents
where do somatic mutation
occurs in somatic cells
what does somatic mutation affect
only individual mutation occurs in
not inherited
where do germ line mutations occur
the germ-line of sexually reproducing organisms
how are germ line mutations caused
May be transmitted by gametes to the next generation
what does a germ line mutation cause
Produces an individual with mutations in both somatic and germ-line cell
what are point mutations
involve only one base pair
what are the two point mutations
- Base-pair substitutions
2. Base-pair deletions or insertions
which bases are double ring
purine
which bases are purine
A G
which bases are pyrimidines
C U T
which bases are singlebing
pyrimidines
what is transition base pair substitution
replacement of a base of the same chemical category (Purine by purine AG or pyrimidine by pyrimidine CT). Represented as: G∙C –> A∙T in double stranded DNA
what is transversion base pair substitution
replacement of a base of one chemical category by a base of the other (Purine by pyrimidine ~A –> C, A –> T,G –> C,G –> T or pyrimidine by purine CA, C –>G, T –> A, T –> G) Represented as: G∙C –> T∙A in the double stranded DNA
what is the effect on protein sequence - nonsense mutations
change of a codon in the ORF (Open Reading Frame) to a stop codon
what is the effect on protein sequences - missense mutations
a base-pair change resulting in a different mRNA codon –> a different amino acid in the protein
what are the phenotypic effects may or may not occur
neutral mutations
silent mutations
what do neutral mutations cause
change of codon in open reading frame, no detectable change in function of protein
what do silent mutations cause
mutant codon encodes same amino acid as wild-type gene –> no change occurs in protein produced
what do base pair deletions or insertions cause
Change the reading frame of the mRNA downstream of the mutation, resulting in frameshift mutation
what happens if reading frame is shifted
incorrect amino acids are usually incorporated
frameshift may bring stop codons into the reading frame, creating a shortened protein
may result in read-through of stop codons, resulting in a longer protein
when do frame shifts occur
result from insertions or deletions when the number of affected base pairs is not divisible by three
are mutations spontaneous or induced
most mutations spontaneous
some are induced
when can mutations occur spontaneously and what causes it
All types of point mutations can occur spontaneously, during S, G1 and G2 phases of the cell cycle, or by the movement of transposons
what is the spontaneous mutation rate in eukaryotes and in bacteria
between 10-4 and 10-6 /gene/ generation, and in bacteria and phages between 10-5 and 10-7 /gene/ generation.
how are spontaneous errors corrected
cellular repair systems, and so do not become fixed in DNA
what is the visible region of
400-700nm
what are induced mutations
caused by physical or chemical mutagens
what are the physical mutations caused by
radiation xrays (ionizing)
what happens when xrays penetrate tissues, what do the created ions do
knock electrons out of orbits and create ions
created ions can break covalent bonds (S-P backbone in DNA)
what do broken bonds in physical mutations lead to
translocations
interchanges between chromosomes
what does ionizing radiation do depending on doses
kills cells at high doses and lower doses produce point mutations
what does UV do to DNA
photochemical changes in DNA
what are UV wavelengths like
UV has lower-energy wavelengths than X-rays, and limited penetrating power
what range of UV is strongly absorbed by purines and pyrimidines what does this form
UV in the 254-260 nm forming abnormal chemical bonds
where do dimers form
Dimer formation between adjacent pyrimidines, commonly thymines
what happens if the abnormal chemical bonds caused by UV mean is enough are unpaired
Most pyrimidine dimers are repaired, as they produce a bulge in the DNA helix. If enough are unrepaired, cell death may result
how do chemical mutations occur what do they do depending on their action
naturally occurring or synthetic
form different groups based on their mechanism of action
what groups can be formed from chemical mutations
base analogues
base modifying agents (alkylating agents, deaminating agents)
intercalating agents
what are base analogues like
similar to normal nitrogen bases, and are incorporated into DNA readily
what happens when base analogues in DNA
shift in the analog’s form will cause incorrect base pairing during replication, leading to mutation
how do base modifying agents work
modifying chemical structure and properties of bases
what does nitrous acid do in base modifying agents
acts as a deaminating agent, converting C to U
what does Ethylmethanesulphonate do
alkylating agent that adds alkyl groups to bases
what are the advantages of using Ethylmethanesulphonate to mutate organisms
not volatile (so it is less likely to be breathed in)
soluble in water (this solution then becomes very mutagenic
Can be left over night and it becomes completely inactive; so it can be disposed of safely
where are intercalating agents inserted
can be inserted between adjacent bases in dsDNA (the sugar backbone)
what do intercalating agents do
alter the spacing of sugar-phosphate backbone of DNA, often causing deletions and associated frameshift mutations, and they do not cause base replacement
how do intercalating agents affect DNA polymerase
DNA polymerase which sticks at a random nucleotides or jumps and affects its fidelity
what is the genetic code
genetic code - more than one codon encoding for one amino acid
what is the biological window in electromagnetic spectrum
300-1000nm
why can’t DNA survive in high radiation e.g.gamma rays, xrays
energy too high
too many mutations
why can’t DNA survive in low radiation e.g. radiowaves
not enough energy for organism to survive
