DNA Synthesis and Repair I&II
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1.replication: each of 2 DNA parental strands serves as template for
synthesis of complimentary strand.
Result: one DNA molecule made of 1 new, 1 parental strand
2.Cell cycle order: [G1, S, G2] interphase, M --> possibly enter G0
3.G1 phase: "gap" phase. variable length. growth and metabolism. cells
spend most time here.
late G1 - prepare to duplicate chromosomes by producing NT precursors
4.G0: extended G1 phase
stimulated to reenter cycle on appropriate signal
5.S phase:: DNA replication
nucleosomes disassemble as replication fork
advances increase histone, DNA associated ptns
synthesis
DNA + histones double
histones complex with DNA forming nucleosomes behind replication
forks
6.G2 phase: 2nd "gap" phase. preparation for cell
division synthesize tubulin (for making
microtubules of spindle)
7.M phase: mitosis: cell divides.
each daughter cell gets exact copy of parental DNA
includes segregation of replicated DNA and
cytokinesis
8.G0 phase: no replication
9.replication fork: site where replication is occurring. (replication origin -
specific sequences. eukaryote genome may have 1000's, bacteria have
one, plasmids have separate origin)
- parental strands separate/unwind before fork
- new strands paired with parental strands behind fork
- replication proceeds into the fork from the origin
10.helicases: separate the DNA strands and unwind the parental duplex
- at replication fork
11.topoisomerases: break phosphdiester bonds and rejoin
them relieve supercoiling of parental duplex by
unwinding
- e.g. gyrase in bacterial cells
- at replication fork
12.singe-stranded binding proteins: prevent parental strands from
reannealing protect from enzymes that cleave ssDNA