Lecture 11-12 Flashcards
What are the types of mutations
i. point mutations
transition purine -> purine - purine or pyrimidine -. pyrimidine
transversion -> purine to pyrimidine vice versa
ii. silent - no change in aa
iii. neautral - properties of aa are simular
iv. missense - aa change that affects protein function
v. nonsence - mutation to a termintion codon
vi. framshift- changes reading frame on mRNA
What are tautomeric shifts and how do that cause mutation
Tuatomeric shifts occure from movment of hydrogren atoms bbetween keto and amino forms and rare (enol and imino) position on a base, leak to replicaiton erroe due to incorrect base pariing
Describe muations induced by cheimicals
alkylatin agents: alter base pairing specifiity, donate methy or ethly groups that modifiy bases
base analogs: subsitutes for usual bases, ex. 5 bromouracil 5BU is a thyminine analog, incrases probability of tautomeric shift
oxidative deamination: nitrous acids converts amino to keto group
intercalting agnets: same dimenations as base pari, wedge between base paris and disorts DNA, causes gaps during replication, inseration or deletion of a SINLGE nucleotide creates frame shifts mutatison
Mutations induced by radiation
ultra violet (UV) light: bases absorb UV at 254 nm, can form thyamine dimers, distrupt base paring during replication
x-rays can break N-glycosidic bond between sugar and base creating apurnic or apyrimidinic sites
What is the ames test
screen for mutagenic compouds measuring ability to convert histide minus (unable to synthesize histidine) mutatnst of salmonella to histidine plus (able to synthesize histidine
Describe the photo reactivation repair mechanisms
only occurs in prokayrotes and uses light eneryg to activate DNA phtolase enzyme to repair thymine dimers
Describe base excisiton repair
a cut and past machansism that removes modified nucleotides and requires a specific glycoasylase (removes base), AP endonuclease and phosphdiesterase (removes sugar-phosphate) followed be inseration of correct nuecltotide by DNA pol and phsphodiester bod formation by DNA ligase
Describe nucelotide excision repair
cut and paste mechanism that can reparin thymine dimers bt removing 12 base stran and requires the acitivies of uvr A, B, C and D proteins in E. coli
in euks, remoes larger stechend of DNA and requires XPA rpetones (mutatined in xerderma pismentosum)
Describe mis match repair
corrects replication errors by a mechanims tha tin E.coli require the mutS, H,L and U proteins, which recognize te newly synthesizes strand by the absence of a mthelyates A in the sequence GATC
Desctibe the SOS response in E.coli
eorro prone repair response that in induced by the Lex A and RecA proteins
Describe post replication rapir in E.coli
usues homolgous recbintion (mediated by RecA) to repair gaps created when the replication fork skps over an unrepaired thymine dimer
How does the doubl strand break repair work
joins nonhomologous end-joining (in which end trimming and blut end ligation reults in some loss of DNA) or by homologous recombination (in which reuqires the Rad proteins
