DNA

1
DNA
Deoxyribonucleic acid

• Structure Replication

2
A Winding Staircase

• DNA is a long molecule that is shaped like a
  spiral staircase
• It is composed of two parallel strands of
  subunits
• Known as a double helix

3
Nucleotides

• Nucleotides are the subunits that make up DNA
• Each nucleotide is made up of three parts
• Sugar Phosphate make up back bone (hand rails
  of the staircase)
• The Nitrogen Bases pair together to connect the
  strands (steps of the staircase)

4
Nitrogen Bases

• In DNA, each nucleotide has the same sugar
  molecule and phosphate group, but it can have one
  of 4 bases
• Adenine
• Thymine
• Cytosine
• Guanine
• The base-pairing rules state that
• Adenine only pairs with Thymine (complementary)
• Cytosine only pairs with Guanine (complementary)
• Base pairs are held together by hydrogen bonds

5
How do cells make more DNA?

• Remember that before mitosis or meiosis can
  occur, DNA must be copied!!
• This process is called REPLICATION
• Steps of DNA replication
• An enzyme (helicase) unwinds separates the 2
  strands of DNA
• New complementary nucleotides are added to each
  side
• Another enzyme (DNA polymerase) joins the newly
  added nucleotides together and proof-reads the
  new strands