DNA Structure and Properties

Physical Structure of DNA

two complimentary chains in opposite polarity, twist around a central axis and form a double helix, right handed helix (B-DNA), BASES ARE NO CO-PLANAR

Chemical composition of DNA

made of many units of NUCLEOTIDES, has TWO polynucleotide chains, and arranged in a DOUBLE HELIX

(Phosphate) Phosphodiester bond

joining successive sugar molecules in a polynucleotide

NucleoSIDE

nitrogenous base + deoxyribose sugar

NucleoTIDE

nitrogenous base + deoxyribose sugar + phosphoric acid

3 major components of a nucleotide

phosphate, sugar, base

Chargaff's Rules

1) # of guanine=# of cytosine, # of adenine=# of thymine, 2) molecular diversity (individual bases vary per species)

3 Examples of Nucleotides

1) nitrogenous base, 2) deoxyribose sugars (5 carbon sugar), 3) Phosphoric acid

2 Nitrogenous Bases

1) purine: a two ringed heterocyclic nitrogenous base, 9 atom ring structure, (adenine and guanine), 2) pyrimidine: a single ringed nitrogenous base, 6 atom ring structure. (thymine, cytosine, uracil)

2 Polynucleotide Chains

2 chains that are anti-parallel (5'-3' phosphodiester bonds are in opposite directions), phosphate molecules on the outside, bases point inward, perpendicular to the helical axis.

2 Sugar Components

DNA (deoxyribose sugar), RNA (ribose sugar)

A-DNA

Dehydrated form of DNA,(NO H20 molecules) double stranded polynucleotide chains, RIGHT hand helical formation, chains are ANTI-PARALLEL and COMPLIMENTARY, very specific base interactions, bases are tilted (not stacked) but still pointed inside the molecule, molecule is wider and shorter than the B‐form, bases are typically in the anti configuration

Z-DNA

Double stranded polynucleotide chains, LEFT hand helical formation with a zig‐zag pattern, chains are anti‐parallel and complimentary, bases are alternate conformation but still pointed inside the molecule, molecule is compact, often seen with repeating purine‐pyrimidine sequences (CGCGCG), bases are in both the syn and anti configurations

B-DNA

Hydrated form of DNA (contains H20 molecules), double stranded polynucleotide chains, RIGHT HANDED helical formation, chains are anti‐parallel/complimentary, very specific base interactions, bases are stacked and pointed inside the molecule, typically in the anti-configuration, specific size constraints on the molecule

Base Pairing

bases linked by hydrogen bonds between oxygen and nitrogen atoms. (purines paired with pyrimidines: A-T base pair, G-C base pair)

N-glycosidic bond

bond that joins a carbohydrate (sugar) molecule to another group

Structure of DNA

double helix, crystalline,