DNA Replication And Repair Flashcards
What is the method of DNA replication ?
Semi- conservative replication method
What is the direction of replication?
Bacteria possess a unique replication origin
Eukaryotes have multiple origin of replication
Replication is bidirectional .
Replication proceeds only in 5 prime to 3 prime direction
Replication on the leading strand is continuous
Replication on the lagging strand is sectional and form Okazaki fragments
What is the enzymology of DNAreplication?
Only deoxyribonucleotide triphosphates can serve as substrates
All DNA polymerase require both a template and primer
RNA polymerase (primate in E.coli) is necessary for the synthesis of RNA primers required for DNA replication
Helicase-unwind DNA
Topoisomerases -catalyze interconversion of different topological isomers of DNA
Single Strand Binding Proteins (SSB)-bind to DNA
What are thee diffferent types of DNA polymerase?
DNA polymerase I-Removes primers and fills in gaps
DNA polymerase II
DNA polymerase III-Major replication type , processive in synthesis
What is the rate of replication error?
Wrong base is incorporates about once every 10 thousand elongation steps
Error rate of exonuclease activity is 1 for 1000
What is the actions of DNA ligase?
Sealed the nick between the fragments of newly synthesized DNA
Necessary for both DNA replication and DNA repair
What are the 5 classes of mammalian DNA polymerase?
Alpha in nuclear-synthesis and priming of lagging strand
Beta (nuclear)-DNA repair
Gamma (mitochondria)- Replicates mitochondrial DNA
Delta (nuclear)-Synthesis of leading strand
Epsilon(nuclear)- DNA repair
What are the main points of eukaryotic DNA synthesis?
PCNA-sliding clamp
RNA primers-Removed by Rnase H
Okazaki-joined by ligase
New histones-one branch of replication fork
What are cyclins?
Cyclins initiates S phase
Control cyclin- dependent kinase activities at various times in the cell cycle
2 types: cyclin A, and E
What are the types of agents that cause DNA damage?
Physical agents
Chemical agents
Damaging agents usually act by altering the structure of nitrogen bases, disrupting normal hydrogen bonding of bases pairs
Multiple enzymes can recognize and remove damaged regions of DNA
What are the type of damage?
Altered bases-thymine dimers caused by UVs
Deamination
Missing bases
Strand breaks that can be single or double
What are the types of repair?
Excision repair-used for thymine dimers
Photoreactivation-not possible in mammals
Base excision repair
Postreplication repair also known as recombinational or SOS repair-error prone repair, last ditch effort
Mistmatch repair-
What are some human repair deficiencies?
Xeroderma pigmentosum-No excision repair
XP variants-Have excision repair but defect in other areas
What are the characteristics of xeroderma pigmentosum?
Sensitivity to ultraviolet radiation
Cancer-skin carcinomas, melanomas
Symptoms- skin and eye photo sensitivity
What are the characteristics of ataxia telangiectasia?
Sensitivity to gamma irradiation
Cancer-lymphomas
Symptoms: ataxia, dilation of blood vessels in skin, chromosome aberrations
