BBMB 405 1nd Edition Lecture 26 Outline of Last Lecture XIV Chapter 28 DNA Replication Repair and Recombination C DNA replication is highly coordinated D Many types of DNA damage can be repaired Outline of Current Lecture XIV Chapter 28 DNA Replication Repair and Recombination D Many types of DNA damage can be repaired Current Lecture XIV Chapter 28 DNA Replication Repair and Recombination D Many types of DNA damage can be repaired 1 Proofreading Pol III contains exonuclease site to chew back mutated DNA strand the mutation creates change in interactions and structure so genome is unstable detects mismatches because of distortions in double helix 2 Mismatch repair MMR a MutS finds lesions damage by finding distortions in helix b MutL assists MutS and recruites endonuclease MutH c MutH recognizes newly synthesized strand d Cleave the DNA then resynthesize e How correct strand identified bacteria Parental strand is methylated so it identifies the unmethylated strand when one strand is methylated and one is not it is called hemimethylation in humans this is not fully understood f Why called mut genes Because if they are not present mutations are far more likely to occur 3 Oxidation Guanine to 8 oxoguanine a Oxidation by reactive oxygen species b Mismatches with adenine through Hoogsteen base pairing These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute c If 8 oxoguanine binds in same conformation as guanine then there is steric clash but if inverts then will only be able to create two hydrogen bonds so bonds with Adenine 4 Deamination Adenine to hypoxanthine a Hypoxanthine is more likely to pair with cystosine b Switch base pair from AT to GC 5 Alkylation Aflatoxin B1 a Aflatoxin is fungal metabolite and a health concern if it is in food sources b Upon digestion cytochrome P450 converts aflatoxin into active DNA modifying agent c Active DNA modifying agent adds something to the base which opens up helix so helix has 12 to 13 base pairs per turn 6 Hydrolysis Remove glycosidic bond to form apurinic or apyrimidinic AP sites a Remove base from sugar b Depurination can occur spontaneously c Both depurination and depyrimidination occur as intermediates during base excision repair 7 Base excision Repair BER a Recognition DNA glycosylases recognize specific lesions b Extrudes base cleaves glycosidic bond c DNA nicking by AP endonuclease d Removal of dRP by deoxyribose lyase e Fill gap by DNA pol and DNA ligase 8 Deamination of Cytosine converts cytosine to uracil which can also lead to damage leads to GC to AT mutations 9 UV light DNA damage a Create thymine dimer activates double bonds and links bonds to create cyclobutane b DNA photolyase not in humans convert energy from light to reverse damage cofactors MTHF 10 Nucleotide excision repair NER a Excision of incorrect nucleotide fragment by UvrABC excinuclease UvrA DNA lesion recognition UvrB DNA binding and UvrC recruitment UvrC cleaves DNA 4 nt downstream and 8 nt upstream of DNA damage b UvrD DNA helicase II removes excised segment c DNA polymerase I resynthesizes DNA and displaces remaining components of UvrABC complex d DNA ligase seals final nick 11 Interstrand crosslinks a Psoralen stack within base pairs then by UV light forms bonds with bases of both strands b Very hard to remove c Generally block replication and lead to arrest of cell division could use to treat cancer 12 DNA damage can be used therapeutically nitrogen mustard connects two adjacent bases in interstrand linkages chemotherapeutics 13 Ames Test a Mutation in the histadine producing genes so histadine must be added b Some can reverse mutation and make histadine c Add liver to culture so the compound would be metabolized like it would in the body they did this to better be able to see how the mutation would effect the cell in real life 14 Huntington s disease Slippage event occurs where polymerase pauses causing DNA to melt and reanneal incorrectly and DNA to be repaired incorrectly 15 Xeroderma pigmentosum Mutation in NER enzyme can t repair UV damaged DNA
View Full Document
Unlocking...