1. DNA
Part 1: The basics

2. Review
DNA
Gene
Protein
Trait

3. So far... The Big Picture Physical traits come from heredity
DNA → Genes → Proteins → Traits
Physical traits come from heredity
Chargraff’s Data
Ratios of DNA molecule => A:T & G:C always close to 1:1
Different percentages for different species leading to different traits

4. What is DNA? DNA is a special molecule
long chains linking four subunits (smaller molecules)
sequence “encodes” genetic information

5. What’s that DNA stuff made of?
Wait on Notes
DNA = deoxyribonucleic acid
The DNA chain is made of many nucleotides joined together (a polymer).
Nucleotides (a monomer)= molecules with
a sugar portion (the “deoxy” form of ribose) [same]
a phosphate group [same]
a nitrogen base [4 different]
Main Idea?
Key Details?

6. The 4 nitrogen bases of DNA are...
Adenine
Thymine
Guanine
Cytosine
How do I remember?
“All Turtles Go Camping”
“All Teachers Get Cranky”

7. DNA Structure

8. Overall Structure
DNA forms into a “double helix,” or a twisted ladder shape
The sugar-phosphate backbone forms the “legs” of the ladder
The bonds between the sugar and phosphate groups form the twist of the helix
The bases paired up between the legs form the “rungs” of the ladder/helix

10. The Double Helix
Weak hydrogen bonds
Strong covalent bonds

11. The 4 Nitrogen Bases of DNA Are...
A always pairs with T
Forms 2 bonds
G always pairs with C
Forms 3 bonds
This ensures that only correct pairs are formed.

12. Practice Problem
If an organism has a 64% GC content, what percent of A, T, C and G does it have?
A =
T =
G =
C = 18 32