Polynucleotides & DNA

Nucleotides --> Polynucleotides

• The Nucleotides Join Together between the Phosphate group of one nucleotide, and between a Sugar of another. This forms a Phosphodiester Bond (made up of the phosphate group and two ester bonds - Phospho-Di-Ester)
• The chain of Sugars and Phosphates is known as the Sugar-Phosphate Backbone
• Polynucleotides can be Broken Down into Nucleotides again by Breaking the Phosphodiester Bonds.

Double Helix

• Two Polynucleotides join together by Hydrogen Bonding Between the Bases.
• Each base can only bond with a particular partner: this is called Complimentary Base Pairing.
• Adenine (A) always pairs with Thymine (T) and Cytosine (C) always pairs with Guanine (G) (I remember it as the straight letters go together, and the curly letters go together)
• A Pyrimidine always pairs with a Purine.
• 2 Hydrogen bonds form between A-T and 3 Hydrogen Bonds form between G-C
• Two Antiparallel (going in opposite directions) polynucleotide Strands Twist to form the DNA Double Helix

Purifying DNA - Precipitation Reaction

1. Break Up Cells using a blender
2. Make a mixture of washing up liquid, salt, and distilled water, this mixture is called the Detergent
3. Add broken cells to a beaker containing the detergent
4. Put the beaker in a Water Bath (60°C) for 15 Minutes.
5. Now, put the beaker in an Ice Bath, then Filter the mixture.
6. Transfer a small amount of the filtered mixture to a clean boiling tube.
7. Add Protease Enzymes
8. Slowly Dribble some cold ethanol down the side of the boiling tube so it forms a Layer on top of the mixture.
9. Leave it for a few minutes and a White Precipitate should form, which can be removed with a Glass Rod.

Self-Replication

DNA can Copy Itself before cell division

1. DNA  Helicase (Enzyme) Breaks the Hydrogen Bonds Between Two polynucleotide DNA Strands - The helix Unzips.
2. Each Original Strand becomes a Template for a new strand. Free-Floating DNA Nucleotides Join to the exposed bases of each original strand by Complementary Base Pairing.
3. The Nucleotides of the New Strand are joined together by DNA Polymerase (Another Enzyme). This forms the Sugar-Phosphate Backbone. Hydrogen Bonds Form between the bases on the Original and New Strand. It then Twists to form a Double Helix.
4. Each new DNA molecule contains One strand from the Original DNA Molecule and One New Strand