Background Information:

The acronym DNA stands for Deoxyribonucleic Acid.dna DNA is the molecule that makes upChromosomes and serves as hereditary information.

Nucleic Acids

There are two types of nucleic acids, DNA and RNA. Remember what you learnt in unit 2 - both DNA and RNA are polymers of nucleotides. (ie. Chains of joined nucleotides). They form genetic material and are involved in the functioning of chromosomes and in protein synthesis.

VIDEO: DNA Structure

The shape of DNA is referred to as a double helix made up of repeatingnucleotide nucleotide units.

Nucleotides are composed of 3 key parts:

i) Phosphoric acid (Phosphate group)

ii) 5 carbon sugar (Deoxyribose)

iii) Nitrogen base:

a) Purines: (**larger base than Pyrimidines**) (Double ring)purine

b) Pyrimidines: (Single ring)pyrimidines

When the bases bond together they form the "rungs" of the DNA ladder and do so in a set pattern. The alternating sugar and phosphates make up the rails (backbone). The bases make up the rungs.

Adenine always bonds to ThymineDNA (Two hydrogen bonds)
Guanine always bonds to Cytosine (Three hydrogen bonds)

This bonding of bases is called Complementary Base Pairing. The bases cannot bond any other way because 2 purines would overlap and 2pyrimidines would be too short to form the rungs of the ladder. The double strand is held in place by hydrogen bonds between the bases. It is the number and order as well as the type of the bases that determine what kind of organism will develop.

Example: ATCCGATT means something entirely different than ACCGTTAT, just as the words Hate and Heat mean different things even though they contain the same letters.

As a DNA strand lengthens, it twists into a double spiral called a Double Helix.