D1.1 DNA Replication

4 reasons why DNA is replicated

• to repair when there is a need to

• to grow an organism

• to reproduce a new generation

• to regulate functions

Describe how a new strand of DNA is semi-conservative

half is a parental strand

half is a synthesised pair of the parental strand made from free nucleotides

How is genetic integrity maintained?

Active site of cbp is accurately manipulated to allow for genetic continuity and accuracy.

explain purpose and process of PCR at 3 temepartures

• purpose: to amplify small amounts of DNA quickly

after all nessecary things are collected in a test tube, it is put in the thermal cycler

1. 98C: DNA is denatured and base pairs are exposed and broken

2. 60C: lab primers anneal to base pairs of DNA strand as a start before nucleotides

3. 72C: Taq polymerase pairs free nucleotides to the remaining exposed bases and bonds the sugar-phosphate backbone

After 30 cycles, how many copies are made?

After 30 cycles, 2 billion copies are made

Why are taq enzymes speical?

• they are heat resistant and therefore can sustain its function through all the cycles of PCR without denaturing

• they were enzymes found in hot springs

Explain gel electrophoresis

1. PCR to amplify the sample

2. Restriction DNA cut bonds of fragments of sequences excluding junk DNA. based on size

3. Samples from different people in a test tube is loaded into wells of a gel slab

4. eletric field is applied to the slab

5. DNA moves towards the + terminal opposite to the wells. Shorter fragments move faster, longer fragments move slower

6. After a certain amount of time, the fragments of DNA bands are suspended in the gel and is dyed to make visible.

Two uses of gel elctropheresis

DNA profiling in 2 categories

1. Forsenic investigations:

Compare for 100% between one sample with several others.

2. Paternity investigations

Compare for 50% match from a child to a mother or father’s DNA

outline the role of the 5 enzymes used in DNA replication

helicase

1. unwind DNA double helix structure

2. break hydrogen bonds of cdp to expose bases for a new pairing

primase

1. attaches a primer (short fragment of RNA) to the parental strand that acts as a starting point for polymerase III

2. There are numerous primers on the lagging strand, but only one on the leading stand

Polymerase III

1. Use the CBP adding of 5’ end of a nucleotide to the 3’ end of a parental nucleotide to build covalent sugar-phosphate backbones

2. Proofread and excises dispaired base and replace with corect nucleotide from the 3’ terminal using exonuclease activity

Polymerase I

1. Removes primers and repalces it with DNA Nucleotides

Ligase

1. Join okazaki fargments using phosphodiester bonds

explain steps of DNA replication

Describe the leading and lagging strand

Leading strand: 3’ end is away from the replication fork, therefore DNA replication can be continuously done as the replication fork expands

Lagging strand: 3’ end is at the replication fork, therefore DNA replication can only be discontinuously done because the polymerase III has to return to the replication fork as soon as it hits the primer.