Double helix structure of DNA “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.” Watson & Crick
Directionality of DNA You need to number the carbons! – it matters! OH CH 2 O 4 5 3 2 1 PO 4 N base ribose nucleotide OH O 3 PO 4 base CH 2 O base O P O C O – O CH 2 1 2 4 5 1 2 3 3 4 5 5
What is DNA Replication? DNA replication is the process in which DNA is replicated to produce an exact copy of itself. DNA replication is carried out in preparation for cell division. Replication is achieved by a single strand of the DNA molecule being used as a template for a new complementary strand . – The replicated DNA consists of one original strand of DNA, and a newly synthesized strand. – DNA replication is thus said to be semi- conservative . Parent chromosome G C A T Replicated chromosome Chromatid Centromere Parent DNA DNA that will become separate chromatids
DNA Replication Large team of enzymes coordinates replication
DNA Replication DNA replication consists of three stages : 1. Unwinding. The DNA strand is unwound to allow replication to occur. 2. Elongation A new DNA strand is made using the original as a template. 3. Termination DNA synthesis is completed, and the new DNA molecule assumes its double helix structure.
Replication: Unwinding The coiled DNA is allowed to This opens up the DNA molecule for replication. Enzymes are involved: helicase : unwinds the strands – DNA gyrase : cuts, winds and rejoins the DNA strand. Single-armed chromosome as found in non-dividing cell Temporary break (swivel point) Replication fork