Ib biology: D1.1: DNA replication

polymerase chain reaction

1. double stranded DNA with known end sequences

2. 95C° to separate/denature double strands

3. make a primer to attach to known end sequence. cool to 40C° so primer can attach to strand

4. add heat tolerant TAQ polymerase, heat at 72C° ( optimal temperature )

5. nucleotides attach to primers using strands as a template

6. repeat ( chain reaction )

short tandem repeats

areas of human genome where there are repeats of codons: don’t code for anything

what is the role of a primer in PCR

• to provide a double stranded region of DNA for the enzyme to bind to

• define the region of the DNA which must be amplified

what is the role of a telomere

• to provide protection during cell division

• facilitates the binding of an RNA primer at the end of a chromosome

• to prevent the shortening of the DNA strand

Albert Hershey and Martha Chase experiment

• showed that DNA is not a protein

• radioactive isotopes where used to label bacteriophages

• proteins - radioactive Sulphur

• DNA - radioactive Phosphorus

• only the DNA from the viruses got introduced

• the bacteria and viruses got centrifuged, thus separated

• the bacteria were only radioactive with sulphur

on leading strand, in what direction does new DNA get synthesised

the RNA primer attaches itself on the 3’ end and produces towards the 5’ end, however the dna strand that it produces is made from 5’ to 3’

helicase

• during dna replication, unwinds double helix by breaking hydrogen bonds

RNA primase

• produces one RNA nucleotide on the area of dna that must be replicated; defines beginning of process

• that nucleotide is the primer; that’s where extra nucleotides are added

DNA polymerase III

• binds dna nucleotides together on leading strand; form the diphosphide bond + sugar phosphate backing on dna

DNA polymerase I

once DNA polymerase III did it’s thing, DNA polymerase I removes the single RNA nucleotide/primer imposed on the dna strand

okazaki fragments

small fragments of DNA synthesised on the lagging side that need to be moved.

ligase

binds okasaki fragments together

single stranded binding proteins

after helicase does it’s thing, binds to each strand to prevent them from reattaching