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• Defined: Molecule that
stores genetic
information
• Monomer: Nucleotide
• 3 parts to nucleotide
– 1) Sugar
– 2) Phosphate Group
– 3) Nitrogen Base
• Millions of nucleotides
bond to make nucleic
acids
• Sugar (Deoxyribose)
connects with the phosphate
group
• 4 Different Bases:
– Adenine (A)
– Thymine (T)
– Guanine (G)
– Cytosine (C)
• Rule: A always joins with T
• Rule: C always joins with G
• Human DNA: ~3 billion pairs
C
T
A
A
T
G
T
• James Watson and Francis Crick identified DNA’s
structure in 1953
• Double Helix: spiral shape of DNA
• Nucleotide strands are connected by a hydrogen bond
• Defined: Process of copying DNA
– During interphase (S-stage)
• Step 1: DNA Helicase “unzips” the two DNA strands
(breaks the H bonds)
• Step 2: Free floating nucleotides (A, T, C, G) match up
• Step 3: DNA Polymerase reconnects the two strands
Step 1:
DNA Helicase
“unzips” the two
DNA strands
(breaks the H
bonds)
Step 2:
Free floating
nucleotides (A,
T, C, G) match
up
Step 3:
DNA
Polymerase
reconnects the
two strands
Both strands are
identical
Both strands are
a mix of old and
new nucleotides
DNA Replication Video Clip
enzyme
• Mutation: change in DNA
sequence
• Mutations can be corrected
– Enzyme “proofreads” DNA
and check/correct errors
• Pre-repair: 1 in 10,000
nucleotides has an error
• Post-repair: 1 in 1 billion
nucleotides has an error
Click here if video won’t play
YouTube: DNA Repair Video
Kobe Kuiz
• Name the three parts of a DNA nucleotide.
• Name the four nitrogen bases and how they pair with
others.
• Fill in the missing DNA nucleotides:
A C ? T ? ? ? G C T ? ? A ? C ? T T
? ? C ? T AT ? ? ? C A ? G ? G ? ?
• List what takes place during the three stages of DNA
replication.
• Where is the DNA mutation?
TAGGCCTGTCGAACAGT
ATCCGGACAACTTGT CA