DNA replication Flashcards
What type of replication is DNA replication?
Semi conservative-each daughter gets an orginal and a new one
Whta enzymes open the DNA helix?
DNA heliacase-uses ATP to undo the hydrogen bonds
What enzyme makes the new DNA in the leading strand?
Just behind the heliacase, a DNA polymerase is on the 3’ end of the chain and adds nucleotides 5’ to 3’. Its a reaction that released tripohsphate, which drives reaction
What Does DNA polymerase require?
A RNA primer to start, a template strand and adNTPs
What are nucleoside analogues? What can they do?
Usually look like bases but cannot make the phosphate backback-terminate replication (etc ddC, drug for HIV), acyclover (drug for herpes)
What is a replication fork?
Replication begins at origin or replication, and fork open (unwound DNA) before the polymerase- the template 3’ and 5’ strand follow on each side, with new strand being synthesised on them
How is the laggin strand replicatd?
Because of its direction, it has to be replicated backwards to be 5’ to 3’. Its done by okazaki fragments (short pieces that start with RNA primer (DNA primase), then DNA poly adds a few Nt (until next primer) and ligased with DNA ligase). usually kept open for a bit by prots between primase (at fork) and DNA polymerase)
Does DNA poly have proofreading?
the “Thumb” of DNA poly acts as proofreading, and can excise dNTPs that are incorect-error rate is 1 per 10^9
How is replication satrted in prokaryotes? What about eukaryotes?
Because they have circular DNAs, the fork starts at OriC and goes down both ways, creating a copy (bidirectional). Eukaryotes dont have ciruclar DNA dna have a lot, so multiple bidirectional forks can happen-and then join at the end
What are the main parts of the cell cycle?
M-mitosis G1-gap 1, before DNA synthesis S-DNA repliaction. nearly as long as g1 G2-between M and S G0-cells that stopped dividing
How are chromosomes organised during the cell cycle?
M-consdensed and moved
G1- each chr is a single linear double helix
S-replicated as beads on a string
G2-present as pairs of identical chromatids
Describe what Interphase is?
Interphase is G2 or G1, which means DNA is not visible and the cell is normal
What is late prophase?
Late prophase is the first step of mitosis-chromosomes are condensed in the nucleus
What os metaphase?
Second step of mitosis-Chr are aligned on central plane and connected to centrosome with microtubules
What is anaphase
3rd part of mitosis-sisters chromatids are pulled to the spindle poles and seperated
