Replication of DNA

• Chromosomes


  Composed of the nucleic acid DNA (Deoxyribonucleic Acid)
• DNA molecule


  Composed of two separate strands wound together into a shape known as a double helix
• Nucleotide


  Made of three different molecules linked together: Phosphate, Nitrogenous base, Deoxyribose sugar
• Each nucleotide links to the next in the sequence by strong sugar-phosphate bonds which form the sugar-phosphate backbone of the DNA molecule
• Organic base molecules in DNA

  • Adenine
  • Thymine
  • Cytosine
  • Guanine
• In 1953, James Watson and Francis Crick discovered that in DNA, the ratio of adenine to thymine bases was always 1:1, and the ratio of cytosine to guanine was also 1:1
• Base pairing


  Adenine pairs with Thymine, Cytosine pairs with Guanine
• Complementary base pairing


  The sequence of bases determines the organism's genotype
• The bases are held together by weak HYDROGEN bonds
• Deoxyribose sugar


  The carbons can be numbered in a clockwise manner
• 3' (3 prime) and 5' (5 prime)


  Identify the direction in which the sugar-phosphate backbones run
• DNA structure comprises nucleotides, sugar-phosphate backbone, base pairing, and double stranded antiparallel structure
• Antiparallel strands


  The sugar phosphate backbones in the two strands of a DNA molecule run in opposite direction to each other
• DNA Replication


  1. DNA is replicated by DNA polymerase

  2. Requires original DNA template, DNA nucleotides, enzymes, and a primer

  3. DNA polymerase adds nucleotides to the 3' end of the growing strand

  4. Primer provides a starting point for DNA polymerase

  5. Leading strand is replicated continuously, lagging strand is replicated discontinuously and joined by DNA ligase
• DNA replication produces two identical copies of the original DNA molecule
• Semi-conservative replication


  Each new DNA molecule is made up of one new strand and one original strand
• Polymerase Chain Reaction (PCR) is a technique that amplifies a piece of DNA
• PCR


  • Requires DNA, nucleotides, enzymes, and primers
  • Involves cycles of heating and cooling to denature DNA, allow primers to bind, and DNA polymerase to replicate the target region
• Practical applications of PCR

  • Genetic testing
  • Forensics
  • DNA mapping