1. DNA – Deoxyribonucleic acid
Polymer
Nucleic acids are biopolymers, or large biomolecules, essential to all known forms of life. They are composed of monomers, which are nucleotides made of three components: a 5-carbon sugar, a phosphate group, and a nitrogenous base. DNA is a type of nucleic acid
Individual unit called a (mono)nucleotide
DNA is the genetic code to synthesise proteins

2. Nucleotide Structure 3 components: Pentose sugar Organic base
Phosphate
sugar
base
Stay the same
Changes
Contains nitrogen & carbon
Pentose sugar
(5 Carbon atoms)
3 components:
Pentose sugar
(ribose in DNA)
Phosphoric acid
Organic base
(always contains nitrogen)

3. Bondings The base and sugar join with a: glycosidic bond
The phosphate and sugar join with an:
ester bond
Both require a condensation reaction to occur 

4. 2 condensation reactions occur in the formation of a nucleotide:
Phosphate
2 condensation reactions occur in the formation of a nucleotide: H
Ester bond OH
Glycosidic
bond OH H
Base
Sugar

6. Nucleotide 3 components: Pentose sugar; deoxyribose Phosphate group
Nitrogenous base; 4 types:
Join by condensation
phosphate
base
Stay the same
sugar
Changes
Contains nitrogen & carbon
Ribose sugar in RNA
Deoxyribose sugar in DNA
Pentose sugar (5 Carbon atoms)

7. You do not need to know this structure for CIE

8. In the backbone of DNA the 5' carbon of one deoxyribose is linked to the 3' carbon of another by a phosphate group. The 5' carbon of this deoxyribose is again linked to the 3' carbon of the next, and so forth.

9. Phosphodiester Bonds: the sugar-phosphate-backbone

10. 4 Bases Purines – Pyrimidines – Double ringed structure Planar
Single ringed structure

11. Complementary Base Pairing
*Purines always pair with pyrimidines*
A joins to T (2 hydrogen bonds)
C joins to G (3 hydrogen bonds)
see

12. Hydrogen bonding Explain how the interaction between base pairs
fits the definition of hydrogen bonding.

13. Bonding relationships
Type of Base
Purine
Pyrimidine
Structure
Bonding relationships
Adenine
Guanine
Thymine
Cytosine
= hydrogen bond

14. 5’
3 hydrogen bonds 3’ C G
0.34nm A T 3’
2 hydrogen bonds 5’
2nm

15. DNA jigsaw…
Sketch the pieces joined in the correct arrangement for DNA. Label: a sugar, a phosphate and a base pair

16. Answer… (are there other possibilities?)

17. The bigger picture…
Can you suggest any other reasons that Adenine always pairs with Thymine and Cytosine always pairs with Guanine?

18. The bigger picture…
Can you suggest any other reasons that Adenine always pairs with Thymine and Cytosine always pairs with Guanine?
Consider the size of the base pairs relative to the distance between the sugar-phosphate backbone.

19. 2 strands run in opposite directions.
Strands are twisted to form a double helix.
The bases link the 2 strands together via H bonds and van der Waals’ forces between one base pair and the next.
Base pairs are always complementary
T & A and G & C.

20. A DNA strand acts as a template for replication.