Chapter 12: DNA and RNA

1
DNA Structure
2
DNA

• Deoxyribonucleic acid
• DNA is a biological polymer
• Made up of subunits called nucleotides
• Each nucleotide is made up of a sugar, a
  phosphate and a base

3
Nucleotide

• Nucleotide- Individual unit of DNA.
• Made of three parts
• Deoxyribose (5-carbon sugar)
• Phosphate group
• A nitrogen-containing base

4

• The phosphate and sugar form the backbone of the
  DNA molecule, whereas the bases form the rungs.

5
Bases

• Four nitrogen-containing bases
• Adenine
• Guanine
• Cytosine
• Thymine

6
Bases

• Adenine
• double ringed
• Guanine
• Thymine
• single ringed
• Cytosine

purines
pyrimidines
7
Base Pairing Rule

• Bases are paired together in specific manner
• Because of chemical structure and shape
• Adenine only pairs with Thymine
• Guanine only pairs with Cytosine
• Exactly enough room for only one purine and
  one pyramide base between the two strands of
  DNA

8
Base Pairing Rule

• Bases held together in rungs by weak hydrogen
  bonds
• 2 hydrogen bonds between A T
• 3 hydrogen bonds between C G

9
DNA
10
DNA Double Helix

• DNA is made of two nucleotide strands that wrap
  around each other in the shape of a double helix.

11

• Bonds Hold DNA Together
• Nucleotides along each DNA strand are linked by
  covalent bonds.
• Complementary nitrogenous bases are bonded by
  hydrogen bonds.
• Hydrogen bonding between the complementary base
  pairs, G-C and A-T, holds the two strands of a
  DNA molecule together.
• Because of this complementary base pairing, the
  order of the bases in one strand determines the
  order of the bases in the other strand.