• Defined: Molecule that
stores genetic
information
• Monomer: Nucleotide
• Millions of nucleotides
bond to make nucleic
acids
• Gene: section of DNA
that holds instructions to
build a protein
Nucleotide
Structure
• Three parts
– Sugar molecule
– Phosphate group
– Nitrogen base
(A, T, C, or G)
• Nucleotides combine
to make nucleic
acids
• A pairs with T
• C pairs with G
T
C
C
G
A
• Sugar (Deoxyribose) connects
with the phosphate group
• 4 Different Bases:
– Adenine (A)
– Thymine (T)
– Guanine (G)
– Cytosine (C)
• Chargaff’s Rules:
– Rule: amount of A = amount of T
– Rule: amount of C = amount of 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 DNA
molecules are
identical
Both DNA
molecules contain
one original
strand and one
new strand.
This is called the:
semiconservative
model
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
YouTube: DNA Repair
The Secret of Our Lives:
The Human Genome Project
Code For Life: The Human Genome
Review
1)
2)
3)
4)
5)
6)
7)
8)
Name the three parts of a DNA nucleotide.
Name the four nitrogen bases.
List Chargaff’s rules.
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.
What type of organic moleules are DNA helicase and
DNA polymerase?
Why is DNA replication considered semiconservative?
Where is the DNA mutation?
TAGGCCTGTCGAACAGT
ATCCGGACAACTTGT CA