AS Biology Structure of DNA

DNA = DeoxyriboNucleic Acid.

Double helix structure.

DNA is a chemical that determines inherited characteristics and it contains genetic code.

Made up of 3 basic components to form a nucleotide. DNA is a POLYnucleotide due to being made up of many nucleotides.

Basic Components = Dioxyribose (pentose sugar), Phosphate Goup and an organic base (A,T,G,C).

Phosphate group \ \ Deoxyribose --------- Organic Base

There are 4 possible organic bases - A = adenine

T= Thymine

G = Guanine

C = Cytosine

Each base can only join to its complimentary bases. A joins to T and G joins to C.

the organic base is the only part of DNA that changes. The phosphate and sugar group stay the same.

Organic bases are of two types; double and single ringed.

Double ringed = A and G, Guanine produces 3 hydrogen bonds

Single ringed = C and T, Thymine produces 2 hydrogen bonds.

Two poly nucleotides join together to form a double helix.

In one strand, deoxyribose joins with the phosphate group to create a sugar-phosphate backbone.

The 2 poly nucleotide strands join together by hydrogen bonds that from between the 2 complimentary bases.

The phosphate group, deoxyribose sugar and organic base are all joined together in a process called condensation.

In every DNA molecule the phosphate group, deoxyribose sugar and 4 bases are the same. It is the ratio quantity of these bases that differs and more importantly, the sequence in which they are in in the double helix.

DNA storage in EUKARYOTIC CELLS>

- Contain linear DNA that exists as CHROMOSOMES.

- DNA molecule is really long and winds up into the nucleus.

- The DNA is wound around proteins; Histone proteins.

- DNA is then wound up very tightly and compact to make a chromosome.

- The DNA is associated with proteins.

DNA storage in PROKARYOTIC-

- Also as chromosomes but DNA MOLECULES ARE SHORTER AND CIRCULAR.

The DNA isn't wound round histone proteins.

The DNA condenses to become more compact by a process called SUPERCOILING.

The DNA isn't associated with proteins like in eukaryotic cells