Flashcards in DNA Replication And Repair Deck (47)
What direction does DNA replication proceed?
5' to 3' direction
DNA is replicated in one smooth, continuous process
DNA is replicated in small sections then fused together
Short section of RNA which is complementary to the template strand and contains free 3' OH group
Separates the DNA strands. Requires ATP.
What reaction does DNA polymerase catalyze?
Hydrolysis of PPi to 2Pi that allows the incoming nucleotide to be bound to the strand.
RNA polymerase that is required to initiate DNA synthsis
Short sections of primer RNA plus DNA that form on the lagging strand. Will be joined together later.
Total proteins and enzymes required for DNA synthesis at a replication fork
Acts to prevent the extreme supercoiling of the parental helix by breaking and rejoining DNA chains. Relieves the tension ahead of the replication fork.
Type I topoisomerase
Makes a break/nick in a strand of DNA helix, passes the other strand thru the break to relax the coil. Removes 1 supercoil
Type II topoisomerases
Requires ATP. *AKA DNA gyrase in E. Coli* Produce break in BOTH strands of DNA. 2 supercoils are removed in one step
Single Stranded binding protein
Keeps the separated strands as single strands. Are displaced and reused as DNA is replicated
DNA polymerase I
Removes RNA primers (5' –> 3' exonuclease activity) and fills in gaps with dNTP that matches the exposed DNA template. Edits/proofreads the strand (3'->5' exonuclease activity), cleaving off any unpaired 3' terminal nucleotide
DNA polymerase III
Major replicative enzyme. Stays on the DNA molecule for long stretches of processing
Enzyme that catalyzes formation of phosphodiester bond b/t 2 Okazaki fragments
Types of DNA mutations
Point mutations, insertions, deletions
substitution of one base for another
Adding one or more nucleotides within a DNA sequence
Removal of one or more nucleotides with a DNA sequence
Steps of DNA repair
Removal, filling of the gap, ligation
Nucleotide excision repair
Removal of a group of nucleotides
Base excision repair
Specific glysosylase that removes a damaged base by hydrolyzing an N-glycosidic bond
What serves as substrates in DNA synthesis?
What do DNA polymerases require for activity?
Primer and template
Works on both Gram - and + bacteria. Effects the supercoiling of bacterial DNA gyrase
All factors required for DNA synthesis
What 4 classes of DNA polymerase are found in the nucleus?
Alpha, beta, delt, sigma
Where is gamma DNA polymerase found?
What 2 classes of DNA polymerase are involved in DNA repair?
beta and sigma
What two chemical reactions are used to disassociate histones from DNA?
Acetylation and phosphorylation
What proteins dictate the phase of replication that the cell is in?
Cyclins (A and E involved in DNA synthesis)
What two types of agents cause DNA damage?
physical and chemical
What causes thymine dimers to form?
Why does a thymine dimer cause disfunction in DNA?
Distorts the helix, so the DNA cannot be replicated without error
What is deamination?
Cytosine converts to uracil, ultimately leading to a C→T mutation
Single Strand break
The phosphodiester bond is broken on a single strand of DNA, is easily repaired.
Double strand break
2 single strand breaks occur near each other on opposite sides of the DNA. Is very hard to repair, and usually results in cell death
When is excision repair used?
Used to repair bulky damages to DNA
When is base excision repair used?
Small modifications to DNA bases
is known as the SOS repair, error prone repair which occurs as a last ditch effort where a random nucleotide is inserted
Excision repair proteins have lost activity, so cannot repair damages, particularly those done by UV. Can have eye photosensitivity
Gamma irradiation sensitivity. Usually have lymphomas, Signs: ataxia, dilation of blood vessels in the skin, chromosomal aberrations
Have a sensitivity to cross linking. Causes leukemias. Signs: hypoplastic pancytopenia, congenital abnormalities
Sensitivity to UV. Causes leukemias. Signs: skin photosensitivity, usually a butterfly shaped rash on the face
Have a sensitivity to UV. Causes various tumor cancers. Signs: neurological defects, dwarfism