The causes of genetic mutatoins Flashcards
what is a mutation
this is a sudden change in genetic trait - it changes the DNA code
the change is….
then heritable – somatic mutation is passed on to daughter cells and if its in a germ mutation is passed onto the next generation
can mutations be good or bad
Both
- positive is that they drive evolutionary change
- the negative is that they cause many diseases
what are the types of mutations that you need to know about
- point mutations
- frameshift mutations
- chromosomal mutations
mRNA codon that you need to know about
- AUG = this is methionine and is a start codon
describe point mutations
- Changes in a single base pair in DNA – these do not interfer much with protein function but can be bad
what are the three types of point mutations
- Silent
- Missense
- Nonsense
describe silent
- Three base codon changes but the same amino acid is coded
describe missense
- Conserved – changes the amino acid coded but one that has similar properties
- Non-conservative – changes amino acid coded to one that has different properties
describe non sense
- Leads to premature stopping of the amino acid sequence
what are the two types of missense mutations
conserved and non conservative
describe examples of point mutations
sickle cell anaemia
describe sickle cell anaemia
- Mutation in a single nucleotide
- Causes change in amino acid from glutamic acid to valine – non conservative missense
- Glutamic acid is a charged amino acid whereas valine is hydrophobic
- Changes in the properties of haemoglobin molecules that carries oxygen to the cells
what are the frameshift mutations
- Where a single base is added or deleted from the DNA
- Adding or deleting 1 base changes every amino acid in the protein after this point
- Proteins don’t function properly
what is an example of frameshift
- tay-sacks disease
describe tay-sachs disease
- Mutations in beta-hexosaminidase A (Hex-A)
- Most are point mutations (65/78)
- 8 frameshift mutations – 6 deletions and 2 insertions,
what are deletions
part of chromosome is left out
what are duplications
part of a chromosome breaks off and attaches to the sister chromatid
what are inversions
part of a chromosome breaks off and reinserts backwards these don’t usually cause any problems as long as its balanced
what are translocations
– part of a chromosome breaks off and attaches to a different chromosome
- changes gene location on chromosome and can change a number of copies of a gene
what are examples of deletions
cri du chat
di George syndrome
what are examples of duplications
Charcot marie tooth disease
what are examples of translocation
XX* male syndrome
describe cri du chat
- Partial deletion of the short arm of chromosome 5
- 90% are sporadic and de novo deletions
describe di George syndrome
- Deletion of a region of a long arm chromosome 22
- Microdeletion
- Majority of cases are de novo
describe Charcot marie tooth disease
- Most common heritable peripheral neuropathy
- 70-80% of cases duplication of large region of short arm of chromosome 17
- Includes gene peripheral myelin protein 22
describe XX* male syndrome
- Translocation of SRY gene from Y chromosome to X chromosome
describe nondisjunction
- Chromosomes fail to separate properly
- Leads to trisomy – extra chromosome – diseases such as down syndrome
- Monosomy – lack of chromosome – usually not viable and frequent in misccariages
- Triploidy – 3 sets of chromosomes – banana plants, sterile and need clonal propagation, in humans triploid babies will miscarry or die within 1st year of life
what are spontaneous mutations
- Arise from errors in replication processes and base modifications
- Eukaryotes = rate 10-4 – 10-6 per gene per generation
- Natural error rate for DNA polymerase
- Many are corrected by cellular repair systems so are repaired before they are transmitted
- Base modifications – depurination, deamination, tautomeric shift
- Base insertion and deletion
what are the origins of spontaneous mutations
can arise by 3 types of chemical changes
- deprivation
- deamination
- tautomeric shift
describe depurination
loss of purine base A or G
describe deamination
changes a normal base to atypical base for example C to U, this can be corrected or 5-methylcyotisine to hypoxantine which is irreparable
describe tautomeric shift
repositioning of hydrogen atoms that lead to mismatching, guanine will pair with thymine rather than cytosine
what is a mutagen
it is an agent which causes genetic mutation
what do mutagens do
they increase the number of mistakes from 1000 to 100,000 per replicated gene
what are the types of mutagens
- physical
- chemical
- biological
name the physical mutagens
- UV rays
- radiation
- extreme heat
name the chemical mutagens
- nicotine
- pesticides
- methane
name the biological mutations
- bacteria
- viruses
what types of radiation is there
- direct
- indirect
describe direct radiation
- When alpha particles, beta particles or x rays create ions which physically break sugar phosphate backbone, connections between base pairs or chemically alter bases
- Bases held together by hydrogen bonds when broken
- If two pyrimidines of the same type (T or C) are next to each other they bind to each other distoriting DNA
describe indirect radiation
- Creation of free radicals where the presence of unpaired electrons damages bases or breaks backbone
what does smoking cause
- 1,000,000 deaths due to lung cancer
- Double strand breaks
- Base pair trans-versions
name infectious agents
- Human papilloma virus – viral DNA is incorporated into host and can disable normal DNA damage repair processes
- Helicobacter pylori – infection can cause stomach cancer and can induce reaction oxygen species
what is a codon
three adjacent nucleotides that Code for an amino acid
name chromosomal mutations
- non dissection
- deletion
- duplication
- inversion
- translocation
