Chromosomes are made of many chromatin threads, each containing DNA and proteins.

Somatic cells contain 46 chromosomes, gametic cells contain 23 chromosomes.

44 of our chromosomes are AUTOSOMES, while 2 are called sex chromosomes.

Each chromosome contains many GENES that act as a blueprint or set of instructions for the cell.

The DNA in chromosomes forms the basis for the genetic code. It alone contains the language of life that determines how a cell operates and all of your characteristics.

DNA is made of long chains of nucleotides. DNA has a DOUBLE-HELIX structure where 2 strands of nucleotides join and twist around to form a spiral staircase or twisted ladder.

Each nucleotide has 3 parts:

1. a phosphate group - helps form the backbone of the DNA molecule

2. a sugar (deoxyribose) - acts as a glue,forms the backbone with phosphate

3. nitrogen bases - 4 types (guanine, cytosine, adenine, thymine)

• the base of one nucleotide forms a hydrogen bond with the base of another nucleotide, thus the bases form the steps of the DNA ladder.
• the sequence of the bases makes up the genetic code

LAW OF COMPLEMENTARY BASE PAIRINGS: adenine and thymine always bind to one another (A-T) and cytosine and guanine bind together (C-G).

Thus the double helix DNA has the complementary bases hidden and protected by the intertwined sugar-phosphate backbones.

DNA FUNCTION

1. Control of cell activities: to produce characteristics of an individual and species
2. Replication: in order for materials to be passed on from cell to cell, generation to generation, and for growth, via meiosis and mitosis.
3. Undergo mutations: permanent changes passed onto offspring may advance the species via evolution