1. Chapter 8
DNA & RNA

2. #1. DNA Structure (an overview)
DNA has three main components
1. deoxyribose (a pentose sugar)
2. base (there are four different ones)
3. phosphate

3. #2. The Bases They are divided into two groups
Pyrimidines and purines
Pyrimidines (made of one 6 member ring)
Thymine
Cytosine
Purines (made of a 6 member ring, fused to a 5 member ring)
Adenine
Guanine
The rings are not only made of carbon (specific formulas and structures are not required for IB)

4. Nucleotides Units that make up DNA molecule Made of three parts
5 carbon sugar (deoxyribose)
Phosphate group
Nitrogen bases

5. #3. Nucleotide Structure
Nucleotides are formed by the condensation of a pentose sugar, phosphate and one of the 4 bases
The following illustration represents one nucleotide

6. #3. Nucleotide Structure
Nucleotides are linked together by covalent bonds called phosphodiester linkage

7. #4. DNA Double Helix and Hydrogen Bonding
Made of two strands of nucleotides that are joined together by hydrogen bonding
Hydrogen bonding occurs as a result of complimentary base pairing
Adenine and thymine pair up
Cytosine and guanine pair up
Each pair is connected through hydrogen bonding
Hydrogen bonding always occurs between one pyrimidine and one purine

8. #4. DNA Double Helix and Hydrogen Bonding
Complimentary base pairing of pyrimidines and purines

9. #4. DNA Double Helix and Hydrogen Bonding

10. Watson and Crick later discovered what held the two strands together
Hydrogen bonds could form between certain nitrogen bases and provide enough force to hold the two strands together
Hydrogen bonds could only form between certain base pairs adenine and thymine and guanine and cytosine
This principal is called Base pairing
This explains Chargaff’s Rule

11. #4. DNA Double Helix and Hydrogen Bonding
Adenine always pairs with thymine because they form two H bonds with each other
Cytosine always pairs with guanine because they form three hydrogen bonds with each other

12. #5. DNA Double Helix
The ‘backbones’ of DNA molecules are made of alternating sugar and phosphates
The ‘rungs on the ladder’ are made of bases that are hydrogen bonded to each other

13. #6. Antiparallel strands5’ 3’
The strands run opposite of each other.
The 5’ end always has the phosphate attached. 5’ 3’