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22 Cards in this Set
- Front
- Back
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What are the four main types of DNA damage?
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1) Depurination (loss of adenine or guanine)
2) Deamination (most easily recognized) 3) Oxidative damage to nucleotides 4) DNA Polymerase error (minor source) |
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What is the result of deamination of methylated cytosine?
What is the result of deamination of normal cytosine? |
Thymine
Uracil |
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What are the five major pathways of DNA repair?
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1) Mismatch repair
2) Base Excision repair 3) Nucleotide excision repair 4) Homologous recombination 5) Non-homologous recombination |
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How does DNA Polymerase tell which strand is wrong (newly synthesized) in mismatch repair?
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There are more nicks in the newly synthesized strand (Okazaki fragment)
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What is the most common type of repair in human cells?
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Excision repair
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What family of enzymes removes damaged nitrogenous bases in Base Excision Repair (BER)?
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Glycosylases
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Which enzymes remove the sugar phosphate in BER?
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AP Endonuclease- cuts 5' end of AP site
AP Lyase- cuts 3' end of AP site (DNAP fills gap and Ligase seals nick) |
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What are two ways in which the pool of dUTP can be increased relative to dTTP?
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1) Inhibition of thymidylate synthetase (dUMP -> dTMP)
2) Folate deficiency (Methylene-THF donates methyl group to dUMP to form dTMP) |
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Which type of repair involves the entire nucleotide(s) due to large structural distortions?
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Nucleotide Excision Repair
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What are the two types of NER?
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1) Transcription-couple repair (removes lesions from transcribed regions, triggered by stalled RNA Polymerase)
2) Global genome repair (removes lesions from all over genome, decreases at terminally differentiated cells) |
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What is the worst type of DNA damage? How do you repair this?
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Double-Stranded Breaks
Repair via Homologous Recombination (dominant mechanism in S and G2) and Non-Homologous End-Joining (dominant mechanism in G1) |
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What enzyme unwinds the DNA in NHEJ?
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PO4-Ku Helicase (phosphorylated by Ku+ kinase)
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What are the requirements of HR?
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1) Homologous sequences
2) Strand invasion and exchange 3) Strand elongation 4) Cleavage and ligation |
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What is the difference in the meiotic and mitotic pathways of HR?
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Meiotic pathway results in crossing over (genetic diversity)
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Which repair mechanism is used to repair broken replication forks?
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Homologous Recombination
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What syndrome results from a defective NER resulting in failure to repair UV-induced damage?
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Xeroderma Pigmentosum
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Which protein acts as a tumor suppressor in cell cycle checkpoint?
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p53
*Loss of this protein allows mutant cells to survive and can possibly lead to cancer |
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What is the name for short, tandem repeats of 1-6 nucleotides scattered throughout the genome?
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Microsatellites
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What factors affect the mechanism of diseases caused by expansion of trinucleotide repeats?
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1) Location of repeats within the gene
2) Function of the affected protein |
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What are the major disease causing mechanisms in the non-coding sequences (introns)?
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1) Decreased transcription (loss of function) (ex: Fragile X)
2) RNA gain-of-function (ex: Myotonic dystrophy) |
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What is the disease-causing mechanism associated with exonic repeats?
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Mutant protein gain-of-function (ex: Huntington's disease)
*most due to expansion of CAG (glu) |
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Name the two proposed mechanisms for abnormal gene expansion
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1) Polymerase slippage of newly synthesized strand
2) Recombination |
