1. DNA

2. Deoxyribonucleic Acid
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

3. Nucleotide Structure A G G C T 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 G C G C C G T A

4. Nucleotides?
How many

5. The nitrogen containing bases are the only difference in the four nucleotides
Nucleotides can be divided into 2 categories:

6. Sugar (Deoxyribose) connects with the phosphate group
4 Different Bases:
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
Chargaff’s rules
Rule: A always joins with T
Rule: C always joins with G
Human DNA: ~3 billion pairs
Nucleotides C T A A T G T

7. Double Helix
James Watson and Francis Crick identified DNA’s structure in 1953 (see video clip: Structure of DNA)
Double Helix: spiral shape of DNA
Nucleotide strands are connected by a hydrogen bond

8. DNA Replication 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

9. Both strands are identical
DNA
polymerase
Step 1:
DNA Helicase “unzips” the two DNA strands (breaks the H bonds) T A A T
Both strands are identical
Both strands are composed of a single strand of old and a single strand of new nucleotides.
This is called the semi conservative model G C G C A T C G
Step 2:
Free floating nucleotides (A, T, C, G) match up T A A T G C G C
Step 3:
DNA Polymerase reconnects the two strands C G T A C G A T
DNA Polymerase
DNA
Helicase

10. DNA Replication Video Clip

11. Accuracy & Repair A T T A T A C G A C T C G G C
Mutation: change in DNA sequence
Mutations can be corrected
DNA Polymerase (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 T A T A C G
enzyme A C T C G G C

12. ReView Name the three parts of a DNA nucleotide.
Name the four nitrogen bases and how they pair with others.
Which nitrogen based are pyrimidines? Purines?
List what takes place during the three stages of DNA replication.
Explain the semi-conservative model.
Fill in the missing DNA nucleotides:
A C ? T ? ? ? G C T ? ? A ? C ? T T
? ? C ? T A T ? ? ? C A ? G ? G ? ?
Where is the DNA mutation?
T A G G C C T G T C G A A C A G T
A T C C G G A C A A C T T G T C A