Bio - D.1.1 DNA Replication

Why DBA replication is needed

1. production of gametes - sex cells during meiosis

2. Growth + repair of tissue - mitosis

Semi - conservative

Replication of DNA - one old + one new strand

When cell = ready to divide - 2 strands of double helix = seperate

Each of original strands acts as template for the creation of a new strand

new strands = assembled through complimentary base pairing

DNA Replication

• Unwinding + unzip double helix with enzyme HELICASE

• Unzips to position called replication fork

• Nucleotides base pair through complementary base pairing

• DNA Polymerase joins together nucleotides - strong phosphodiester bonds

• DNA polymerase only adds nucleotides in 5’ to 3’ direction

• Double strand reforms a double helix

Polymerase chain reaction

• Used for making copies of DNA artificially

• Used to amplify/make millions of DNA copies

• Taq polymerase = heat resistant version of DNA polymerase

• PCR = Cloning DNA at rapid speed

• Temperature used instead of enzymes to break H bonds - 95 degrees

Gel Electrophoresis

• Fragments of DNA move in electrical field and are separated

• Separation = based on size/mass

• Sample of DNA = placed on wells ong el

• Electrical current = passed across gel

• DNA = negatively charges - when electrical current is passed through

  • DNA fragments move to positive electrodes

• Large Fragments move slow

• Small fragments move quicker

Gel electrophoresis used in DNA profiling

• Used to differentiate between individuals

• Technique can be used for:

  • Forensic crime investigations - see if suspects DNA match DNA on scene

  • Parentage issues

  • Animal breeding

  • Disease detection

HL - DNA replication

• Takes place during S section of interphase

• 5’ to 3’

• Antiparallel strands

1. Replication begins at sites ‘origin of replication’

2. Helicase attaches + unzips and unwinds - breaks hydrogen bonds

3. Gyrae keeps DNA strands separated

4. RNA Primase synthesises small amount of RNA primer (will be changed to DNA)

5. DNA polymerase III can only join Nucleotides in 5’ to 3’

   1. only nucleotides can join to 3’ end called leading strand

1. On other side DNA polymerase works away from replication fork

2. Create small fragments - Okazaki fragments - Lagging strand

3. Several primers - one between each fragment

4. Enzyme Ligase joins okazaki fragments to form one continuous DNA molecule

5. DNA polymerase I replaces RNA primer with DNA

DNA polymerase 3 can check its work and repair mismatched bases