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DNA Structure
Pages 196-199
Structure of DNA
 DNA is made of
repeating units of
nucleotides
 A nucleotide has
three parts:
 Deoxyribose sugar
 Phosphate group
 Base
DNA Bases
 Purines
(two ringed)
 Adenine and
Guanine
 Pyrimidines
(one ringed)
 Thymine and
Cytosine
Base Pairing Rules
 Adenine pairs with Thymine
 Guanine pairs with Cytosine
 Chargaff ’s Rule: The
amount of adenine always
equals the amount of
thymine, and the amount of
guanine equals the amount
of cytosine.
DNA Bonds
 Hydrogen bonds hold
bases together
 Covalent bonds hold
backbone together
 The backbone is made of
alternating phosphate
and deoxyribose sugars
The Double Helix
 Double Helix: Phrase
used to describe shape
of DNA
 Double stranded,
coiled like a spiral
staircase