DNA Structure and Replication

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DNA Structure and Replication

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The Structure of DNA

• Many scientists studied the chemical structure of
  DNA
• They found that it was composed of nucleotides
  and had a helix shape
• Scientists James Watson and Francis Crick put all
  of the information and evidence together and
  determined that DNA has a double-helix structure
  and is held together by weak hydrogen bonds.

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Nucleotides

• As we learned before, a nucleotide is made of
  deoxyribose sugar (or ribose in RNA), phosphate,
  and a base (C, G, A or T).
• The sugar and phosphate make up the backbone,
  or long sides
• The bases make up the rungs of the DNA ladder

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What are purines and pyrimidines?

• Purines are the 2 larger bases found in DNA. They
  are adenine and guanine.
• Pyrimidines are the 2 smaller bases found in DNA.
  They are cytosine and thymine.
• In DNA, guanine always pairs with cytosine, and
  adenine will always pair with thymine.
• C-G, A-T

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The process of DNA copying

• Remember that before a cell can divide, it must
  make copies of its DNA. This is done during the
  process of DNA replication
• 1. The DNA unzips and becomes two single
  strands.
• 2. Then the enzyme DNA polymerase is used and
  complementary bases pair up to each strand.
• 3. Finally, each original strand joins its
  complementary strand to form 2 identical DNA
  strands.