DNA Structure

1
DNA Structure Properties
2
Hierarchy in Chemical Structure

• Nucleic acid (DNA or RNA)
• Nucleotide (N-base pentose sugar phosphate)
  e.g. Adenylate, Thymidylate, Cytidylate,
  Guanylate
• Nucleoside (N-base pentose sugar).e.g.Adenosine,
  Thymidne, Cytidine Guanosine

3
Chemical Structure
Chemical Structure of Adenosine triphosphate
Ball-stick Model for Adenosine triphosphate
4
Chemical Structures

• Show DNA Rasmol

5
DNA

• Deoxyribonucleic acid
• Genetic material of most organisms
• Polymer of Nucleotides Nitrogenous base, A, T, G
  C) sugar (ribose) phosphate group
• Watson Crick elucidated DNA structure based on
  X-ray diffraction studies
• Watson-Crick double helix

6
DNA Structure

• Sugar-phosphate backbone
• Pairing between complimentary N-bases
• Adenine pairs with Thymine via Hydrogen bonds
  (double bond)
• Guanine pairs with Cytosine via Hydrogen bonds
  (triple bonds)
• The phosphates stick out into the solvent

7
DNA Physical Properties

• Rigid (because of hydrogen bonding between
  bases, particularly G C
• Very long molecule
• Heating separates strands by breaking hydrogen
  bonds between bases-called Denaturation.
• On cooling bonds are re-formed- Annealing.
• Denaturation causes a decrease in solution
  viscosity.

8
DNA Properties contd

• DNA precipitates in alcohol.
• Long strands of DNA can be spooled on glass
  rods in alcohol.
• DNA is minimally solvated in alcohol.
• Phosphate groups on DNA stick out into the
  solvent allow DNA to be solvated.
• Greater solvent Dielectric constant, greater the
  degree of DNA solvation

9

• Bonds are formed between the sugar of one
  nucleotide phosphate group of preceding
  nucleotide- phosphodiester bonds.
• Phosphodiester bonds can be digested by
  Deoxyribonucleases, e.g. DNAse I

DNAse I digestion
10
Replication, Transcription Translation

• Central Dogma in Biology
• DNA
• RNA
• Protein
• Copying DNA strands is called replication.
• Synthesis of RNA based on one DNA strand (called
  template) is transcription.
• Synthesis of proteins from RNA is called
  translation.