1. DNA
Structure

2. DNA Structure
DNA consists of two molecules that are arranged into a ladder-like structure called a Double Helix.
A molecule of DNA is made up of millions of tiny subunits called Nucleotides.
Each nucleotide consists of:
Phosphate group
Pentose sugar
Nitrogenous base

3. } NUCLEIC ACIDS Nucleic acids are polymers Monomer---nucleotides
Nitrogenous bases
Purines
Pyrimidines
Sugar
Ribose
Deoxyribose
Phosphates
+nucleoside=nucleotide }
Nucleosides

4. The Sugars A Nucleotide consists of :
a nitrogenous base: purine (Adenine (A) or Guanine (G)) or pyrimidine (Cytosine (C) or Thymine (T) (or Uracil (U)in RNA)).
a sugar : Deoxyribose (DNA) or Ribose (RNA).
a phosphate group
A sugar and a base form a Nucleoside. A Nucleotide is a phosphorylated nucleoside. Inter-nucleotide linkages are formed by a phosphodiester bond between a 5'-phosphate group and the 3'-hydroxyl group of the next nucleotide sugar. The nucleotide sequence encodes the information required for constructing proteins.

5. Bases of DNA (and RNA) Purines: Pyrimidines: DNA only RNA only
NOTE: deamination of cytosine= Uracil
Deamination of methyl-cytosine =thymine
Demethylation of thymine= uracil
RNA only
DNA only

6. NUCLEOTIDES
Phosphate
Nitrogenous
Base
Pentose
Sugar

7. Nucleotides
The phosphate and sugar form the backbone of the DNA molecule, whereas the bases form the “rungs”.
There are four types of nitrogenous bases.

8. Nucleotides Each base will only bond with one other specific base.
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
Form a base pair.
Form a base pair.

9. Nucleotides and Nucleosides
Nucleosides consist of a base (pyrimidine or purine) attached to a sugar (ribose or deoxyribose).
Nucleotides are nucleoside phosphates
Nucleotides may be nucleoside monophosphates, diphosphates or triphosphates or NMPs, NDPs, and NTPs, respectively

11. DNA Stabilization– Complementary Base Pairing
Point out purines and pyrimidines. Note how the width can be maintained by the pyrimidine/purine pairing .

12. Chemical Structure of DNA and RNA
Figure 4.1
The C is
named 1’-5’ 4’ 1’ 2’
Nucleotide
Nucleoside
RNA
DNA

13. DNA Stabilization--H-bonding between DNA base pair stacks

14. Physical Structure

15. DNA is Dynamic Like proteins, DNA has 3º structure
Why so many deviations from normal conformation?
Effects on transcription (gene expression)
Enhances responsiveness
May also serve in packaging
NOTE: most cellular DNA exists as protein containing supercoils
DNA has 3º structure.
All these deviations from the normal conformation give living systems another means by which the can regulate transcription (i.e. gene expression). Enhances responsiveness. May also serve in packaging.

16. DNA Structure
Because of this complementary base pairing, the order of the bases in one strand determines the order of the bases in the other strand.

17. DNA Structure
To crack the genetic code found in DNA we need to look at the sequence of bases.
The bases are arranged in triplets called codons.
A G G - C T C - A A G - T C C - T A G
T C C - G A G - T T C - A G G - A T C

18. DNA Structure A gene is a section of DNA that codes for a protein.
Each unique gene has a unique sequence of bases.
This unique sequence of bases will code for the production of a unique protein.
It is these proteins and combination of proteins that give us a unique phenotype.

19. THANKYOU