Causes of genetic mutations

Anna Hogarth
Flashcards by Anna Hogarth, updated more than 1 year ago More Less
Anna Hogarth
Created by Anna Hogarth about 2 years ago
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Dr. L Robson 06.10.17

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Question Answer
What is the difference in heritability of somatic and genetic mutations? Somatic mutations are passed on to daughter cells while germ mutations are passed onto the next generation
Give an example of a positive evolutionary trait Duplication - if one copy of a gene fails then there is back up
What are the three types of mutation? 1) Point mutations 2) Frameshift mutations 3) Chromosomal mutations
What is triplet for the start codon? AUG - methionine
What mutation causes sickle cell disease? What does this result in? 1) A non-conservative change (T to A) which results in a non-conservative mutation of glutamine (neutral) to valine (hydrophobic). 2) This causes the misfolding/malformation of the haemoglobin molecule which carries oxygen. The change from a neutral to hydrophobic amino acid results in the formation of fibres which can cause the blood cells to sickle.
Give an example of a disease caused by a frameshift mutation Tay-Sachs disease
Where do the mutations in Tay-Sachs disease occur? What are the different types of mutations? 1) Mutations in B-hexosaminisade A (Hex-A) 2) Point mutations (65/78), 8 frameshift mutations (6 deletions, 2 insertions).
What is the most common mutation in Tay-Sachs? A 4 base pair insertion in exon 11, observed in 80% of Tay-Sachs disease in Ashkenazi Jewish population
What is B-hexosaminidase A (Hex-A)? A protein in the CNS which is important in the production of myelin
What are the four kinds of chromosomal mutations? 1) Deletions - part of the chromosome is left out 2) Duplication (insertion) - part of a chromosome breaks off and attaches to the sister chromatid 3) Inversion - Part of the chromosome breaks off and reinserts itself backwards 4) Translocations - Part of a chromosome breaks off and attaches to a different chromosome
What tends to be the result of an inversion? Often silent as all the genes and promoters are still present - DNA is read in opposite direction but still effective
When can translocations be beneficial? Can lead to variation which can result in an evolutionary advantage
What is Cri du chat? What do the mutations tend to be? 1) Partial deletion of the short arm of the chromosome 5 (5p) 2) 90% are sporadic and de novo deletions
What is Di George syndrome? What are the majority of cases? 1) Deletion of a region of long arm of chromosome 22 (22q11.2) (microdeletion) 2) Majority of cases are de novo.
What are the genes in the 5p important for? Chromosomal regulation of development - deletion results in neurons not wiring correctly
When do most de novo mutations occur? During meiosis
What is Charcot Marie Tooth disease (CMT1A)? What causes the majority of cases? 1) Demyelination of the peripheral nerves 2) 70-80% of cases are due to duplication of a large region of the short arm of chromosome 17 (17p11.2) - this region contains the gene for peripheral myelin protein (PMP22). There are two copies of PMP22 gene, this increases the amount of PMP22. Myelin which has too much PMP22 results in the incorrect ratio of other proteins. This leads to poor quality myelin and demyelination.
What is XX male syndrome? How is it inherited? 1) The SRY translocates from the Y chromosome to the X chromosome in the sperm. Consequently an individual with two X chromosomes may be male 2) Paternally inherited
What is non-disjunction Chromosomes fail to separate properly
Why do bananas require clonal propagation? Bananas are triploid and therefore sterile.
What happens to human triploid babies? Human triploid babies will miscarry or die within their first year of life.
Screen Shot 2017 10 24 At 18.49.57 (binary/octet-stream) On the LHS is Turner syndrome (XO) on the RHS is Klinefelter syndrome (XXY)
What are the four causes of non-heritable mutations? 1) Spontaneous mutations (mistakes which happen during replication) Induced: 1) Radiation 2) Chemicals 3) Infectious agents
Give four examples of chemicals which may cause mutations 1) cigarette smoke 2) nitrate and nitrate preservatives 3) barbecuing 4) benzoyl peroxide
Give two examples of infectious agents which may cause mutations 1) Human papillomavirus - viral DNA is incorporated into host and can disable normal DNA damage repair process 2) Helicobacter pylori - infection can cause stomach cancer and induce reactive oxygen species.
Describe the mutation rate associated with H. pylori. 1) Up to four weeks following infection there is a mutation burst of around 2.2-8.4X10^-4 changes per site per year (acute infection triggers mutation burst) 2) Beyond 4 weeks (chronic infection) the mutation rate dramatically decreases to 0.5-2.5X10^-5 (equilibrates with host)
Describe the two hit theory Cancer requires two hits - usually there is a spontaneous mutation early on (or inherited) and then a second later hit (which can be environmental or spontaneous). 5% are inherited, 29% are from the environment and the rest are spontaneous.
How many spontaneous mutations happen everyday in the body? 10 to 100,000 - are successfully repaired
What are the stages at which spontaneous mutations can occur? During the S, G1 and G2 phases of the cell cycle or movement of transposons (jumping genes).
In eukaryotes what is the spontaneous mutation rate? 10^-4-10^-6 per gene per generation - RNA polymerase has a natural error rate.
What is a mutagen? An agent which causes a genetic mutation
What effect do mutagens have on the number of mistakes made per gene? Increases it from 1,000 to 100,000 per replicated gene
What are the three classes of mutagens? Give examples. 1) Physical (UV rays, radiation and extreme heat) 2) Chemical (nicotine, pesticides and methane) 3) Biological (bacteria, viruses)
What are the three ways by which spontaneous mutations can occur? 1) Depurination (most common, loss of a purine base - A or G) 2) Deamination 3) Tautomeric shift
What is depurination? A loss of a purine base (A or G)
What is deamination? What are the two forms? 1) Change from a normal base to an atypical base 2) Repairable - C to U; irreparable such as deamination of 5-methylcytosine and hypoxanthine
What is a tautomeric shift? A base is changed by a repositioning of hydrogen
What three things contribute to replication errors? 1) DNA polymerases 2) Endogenous mutagens which leads to 3) Mutagenic nucleotides
What are the repair systems in place to protect against the processes on the previous card? 1) Sanitisation of the mutagenic nucleotide If replication errors do occur then before next replication there should be 2) Proofreading 3) Mismatch repair
What contributes to spontaneous DNA damage? What in turn does spontaneous DNA damage contribute to? 1) Endogenous mutagens 2) Replication errors
How can spontaneous DNA damage be corrected? How can spontaneous DNA damage lead to mutations? 1) Error free repair 2) Error-prone repair results in the mutation being carried through
What is sanitisation usually? Apoptosis
When is repair most effective? During the replication phase of the cell cycle - double stranded loss of a purine is repairable as there is still an existing template. Single stranded is harder because the RNA is 'not aware' of the damage.
What type of action does radiation have? Direct and indirect
Describe the direct action of radiation a- or B-particles or x-rays create ions which physically break the sugar phosphate backbone, connection between base pairs, or chemically alter bases.
What happens to adjacent pyrimidines if the backbone is broken? What does this result in? They interact via hydrogen bonds which distorts the DNA. The 'kinked' section is then either excised or ignored when the DNA is read - either way this results in a loss of a base.
Describe the indirect action of radiation Creation of free radicals, where the presence of unpaired electrons damages bases or breaks backbone - radiation causes the loss of an electron from water causing the production of a substance such as superoxide.
How many deaths are estimated to occur due to smoking related cancer and other neoplasms? 1,000,000 (30% of all cancer deaths in developed countries)
How many carcinogens are there in a cigarette? More than 60
What do the carcinogens in a cigarette cause? Double strand breaks, base pair trans-versions
List some of the toxins in a cigarette Hexamine, arsenic, carbon monoxide, ammonia, methanol, nicotine, acetic acid, butane, methane, hexamine, cadmium, stearic acid, toluene.
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