Polynucleotides + DNA

• Describe and explain the steps in extracting DNA

  • Blend (homogenise) sample with salt + distilled water to break cells apart from each other.
  • Sit in detergent for 5-10 minutes - Disrupt cell membrane
  • Add protease (+RNAse) to break down histones and separated DNA from proteins.
  • Filter and add ice cold ethanol at 45 degrees to form a layer.
  • Extract Dna (white precipitate) using a stick inbetween the solution and ethanol.
• Nucleotides join together to form polynucleotides.
• The nucleotides join up between the phosphate group of one nucleotide and the sugar of another via a condensation reaction. This forms a phosphodiester bond.
• A phosphodiester bond consists of a phosphate group and 2 ester bonds.
• The chain of sugars and phosphate is known as the sugar-phosphate backbone.
• Polynucleotides can be broken down into nucleotides again by breaking the phosphodiester bonds (using hydrolysis reactions).
• Two polynucleotide strands join together to form a double-helix.
• Two DNA polynucleotide strands join together by hydrogen bonding between the bases. Each base can only join will one particular partner - this is called complementart base pairing.
• Adenine always pairs with thymine (A - T) and cytosine always pairs with guanine (C - G)
• Adenine and Guanine are both purines which always pair with pyrimidines
• Cytosine and thymine are both pyrimidines which always pair with purines.
• Two hydrogen bonds form between A and T, and three hydrogen bonds form between C and G.
• Two antiparallel polynucleotide strands twist to form the DNA double-helix.
• DNA copies itself before cell division so that each new cell has the full amount of DNA.