Th2L02 DNA damage and mutations


Medicine Y1 (Theme 2 | Genetics) Flashcards on Th2L02 DNA damage and mutations, created by Emma Allde on 21/08/2016.
Emma Allde
Flashcards by Emma Allde, updated more than 1 year ago
Emma Allde
Created by Emma Allde over 7 years ago

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Question Answer
What are the 3 forms of induced mutation and what are their main mechanisms of action Physical (ionising radiation) ( single or double strand breaks), UV light (causes thymine dimers) and chemical (agents that react with nuclear bases)
What is UV-C (180-290 nm) Light found in daylight as it is absorbed by the ozone layer; the most energetic and lethal
What is UV-B (290-320 nm) The major mutagenic fraction of sunlight
What is damage causes by UV irradiation chemical bonds between adjacent thymines distorting DNA and causing problems during DNA replication, often resulting in point mutations
What is Nitrous acid an example of Chemical agent that results in (CG > TA) point mutation
What is Alkylating agents an example of Chemical agent that results in guanine modification, GC > AT
What are Free radicals examples of (strand breaks and base modification) Chemical agent
What are free radicals ○ Unstable, highly-reactive molecules created during normal metabolism and in response to environmental factors ○ May play a role in the development of cancer, cardiovascular disease, and other diseases of aging by reacting with and damaging DNA and other parts of cells.
What is Xeroderma pigmentosum (XP) a mutation that results in defects in a single strand nucleotide excision repair (NER) gene (XP-D), which prevents repair of thymidine dimers as it encodes for helicase required for NER
What are the symptoms of Xeroderma pigmentosum (XP) Dry skin w/ melanoma and other cancers by about 1000x ("children of the night")
What are the general characteristics of cancer cells Do not grow old and die No reproductive limit
How many mutations are sufficient to turn healthy somatic cell to a cancerous cell To the point where DNA polymerase will not recognise mutated strand 5-6 mutations
How many (%) of human primary tumours test positive for telomerase activity 85%
What kind of point mutations are there (4) • Silent (synonymous) • Missense (non-synonymous) • Nonsense • Indels
What is a silent mutation a single point mutation that doesn't change the coded amino acid e.g. CGA (Arg) -> CGG (Arg)
What is a missense (non-synonymous) a single point mutation that DOES change the coded amino acid e.g. Sickle cell anaemia (GAG (Glu) > GTG (Val)) N-Ras (CAA (Gln) > CAC (His))
What is a nonsense mutation a single point mutation that does not coded for an amino acid e.g. a STOP or START codon instead where there shouldn't be one TGC (amino acid codon) > TGA (stop codon) resulting in trunkated polypeptides
What are indels (mutations) small scale insertions and deletions
What kind of indels exist (2) Insertions/deletions with multiple of 3 that maintain of reading frame Insertions/deletions NOT with multiple of 3
loss of 508th codon in CFTR > cystic fibrosis when homozygous is an example of what kind of mutation Insertions/deletions with multiple of 3 that maintain of reading frame
Which mutation results in frame shifts resulting in non-native polypeptides which can be catastrophic Insertions/deletions NOT with multiple of 3
What is Huntington's disease an example of Serious consequences of small scale insertion/deletion namely: Trinucleotide CAG (glutamine) repeat on huntingtin gene (from 10-34) to (36-121) > neuronal decay
What happens as a result of loss of 32bp in CCR5 Individuals homozygous for change in 32 CCR5 allele are resistant to HIV-1
What is CCR5 The binding receptor HIV goes for on macrophage
What is cri du chat A chromosomal deletion in chromosome 5p that results in children who are mentally retarded, have small heads, and have a cry that sounds like a loud cat The children die at a young age
What is Chronic myelogenous leukaemia (CML) A genetic disease due to translocation where a portion of chromosome 22 gets swapped with a piece of chromosome 9 resulting in a Philadelphia Chromosome Its a cancer affecting white blood cells
What are the 3 examples of spontaneous mutation - errors in DNA replication which escape proofreading and repair mechanisms - replication slippage - deamination
What is replication slippage Gain of repeats - reverse slippage Loss of repeats - forward slippage
What is deamination ○ The removal of an amino group from an organism, particularly from an amino acid ○ C will then pair with A and A will then pair with C, e.g.
What causes human immunodeficiency virus (HIV) an enveloped RNA retrovirus infects CD4 T cells and uses the enzyme reverse transcriptase to mediate synthesis of proviral DNA which integrates into the host cell genome
What do CD4 T cells do Recognises and binds to MHC II antigens and helps stabilise the binding of antigenic determinants to T cell receptor
What do the high mutations rate of HIV genome result in drug resistant viruses
What do early HIV symptoms resemble Influenza: Fever Chills Rash Night sweats Muscle aches Sore throat Fatigue Swollen lymph nodes Mouth ulcers
What does Azidothymidine (AZT) do Inhibits multiplication of HIV and other retroviruses by blocking reverse transcription and production of virally encoded DNA
What is the main issue with Azidothymidine (AZT) Eventually patients stopped responding to treatment
What is the HIV mutation rate 10^-3 per base One of the highest of any virus (or anything else) observed to date 1 x 10^6 faster than human genome
What is the typical mutation rate of a eukaryotic genome 10^-9 per base
What is reverse transcriptase An DNA polymerase enzyme encoded by some certain viruses (retroviruses) that uses RNA as a template for DNA synthesis
What features of reverse transcriptase make it so lethal (2) • More error prone their other nucleic acid polymerases • Does not possess an exonuclease 3' to 5' so does not have any proofreading capacity
What is Acute myeloid leukaemia • A cancer of the blood in which a person produces faulty white blood cells • Immature white blood cells are overproduced and they crowd the bone marrow and cause it not to make normal blood cells
What do all forms of AML have in common the same 9 mutations
Which genes are mutated in AML (3) oncogenes, tumour suppressors and novel genes
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