Chapter 11- DNA replication 

The genome and DNA replication

DNA is replicated in S “synthesis” phase of the cell cycle; DNA exists as chromatin (DNA wrapped around chromosomes)

Know the experiments that determined that DNA was the genetic/hereditary material and how it replicates (Griffith; Hershey & Chase; Meselson & Stahl)

All of the cell’s DNA is its genome; DNA is wrapped around proteins called histones to form chromatin, which is further condensed into chromosomes during mitosis Somatic (body) cells contain 2 copies of each chromosome; Gametes (reproductive) cells have one copy of each chromosome

DNA structure and base-pairing rules dictate replication; DNA undergoes semiconservative replication (each parental strand is used as a template for creating each new strand) – each new DNA molecule is a hybrid of an old strand and a new strand (understand Meselson and Stahl experiment that determined this).

Origin of replication and replication fork is where replication starts; enzymes involved in replication (helicase, SSB proteins, topoisomerase, primase, DNA polymerase, DNA ligase)


name

function

helicase

untwist the double helix at the replication forks

SSB proteins

bind to stabilize single stranded DNA

topoisomerase

relieves the strain caused by tight twisting ahead of the replication fork by breaking and rejoining DNA strands

primase

builds a short RNA primer and uses the parental DNA as a template

DNA polymerase 

the enzyme that builds DNA strand

DNA ligase

the enzyme that joins okazaki fragments

replisome

contains the enzymes responsible for DNA synthesis around the replication fork joined into one large, multi-enzyme machine

DNA is synthesized in the 5’ • 3’ direction...ALWAYS

DNA replication is antiparallel and bidirectional; there is a leading strand and a lagging (discontinuous) strand

Know the order of events in the lagging strand: how is the lagging strand made – what are the steps (Okazaki fragments) and enzymes involved

  • along one template strand of DNA, the DNA polymerase synthesizes the leading strand continuously moving towards the replication fork. 

  • on other template, DNA polymerase synthesizes the lagging strand discontinuous, moving toward the replication fork. 

    • after the formation of okazaki fragments, DNA polymerase I removes the RNA primer and replaces the nucleotides with DNA. 

  • the remaining gaps are joined together by DNA ligase

DNA Replication and Repair