DNA deoxyribose nucleic acid present in the nucleus

DNA = deoxyribose nucleic acid -present in the nucleus of all cells in all living organisms -controls all the chemical changes which take place in cells -decides type of cell which is formed and the kind of organism made

DNA molecule DNA is a very large molecule made up of a long chain of sub-units called nucleotides Each nucleotide is made up of -a sugar called deoxyribose -a phosphate group -PO 4 and -an organic base.

The bases The most common organic bases are Adenine (A) Thymine (T) Cytosine (C) Guanine (G)

Nucleotides The deoxyribose, the phosphate and one of the bases Combine to form a nucleotide PO 4 adenine deoxyribose

Joined nucleotides PO 4 A molecule of DNA is formed by millions of nucleotides joined together in a long chain PO 4 sugar-phosphate backbone + bases

In fact, the DNA usually consists of a double strand of nucleotides -sugar-phosphate chains are on the outside (sides of ladder) -bases bond together in the middle (rungs of ladder) and hold strands together

2 -stranded DNA PO 4 PO 4 PO 4 PO 4

Bonding 1 The bases always pair up in the same way Adenine forms a bond with Thymine Adenine Thymine and Cytosine bonds with Guanine Cytosine Guanine

Bonding 2 PO 4 adenine thymine PO 4 cytosine guanine PO 4

Pairing up PO 4 PO 4 PO 4 PO 4

The paired strands are coiled into a spiral called A DOUBLE HELIX -structure of DNA credited to James Watson & Francis Crick (1953)

THE DOUBLE HELIX bases sugar-phosphate chain

A DIY model of part of a DNA molecule

• Genetics: The study of genes or heritable traits – Genetics determine both physical and behavioral traits. Our traits are encoded on sections of DNA called genes, which come in pairs, one from mom and one from dad.

• DNA: deoxyribose nucleic acid – a molecule that stores genetic information for hertiable traits and directs the structure and function of cells • Chromosomes: In a cell, tightly packed strands of DNA visible under a light microscope duirng cell division – Our chromosomes come in pairs: the sperm contributes 23 and the egg the other 23 for a total of 23 pairs (46 individual chromosomes). • In order from big small: – Chromosomes DNA genes nucleic acid

• Gene: a section of DNA on a chromosome that codes for a specific protein and function • Genetic Code: The sequence of bases along the DNA molecule • Determined by Watson and Crick, the structure of DNA can be compared to a twisted ladder. Actual name of shape is Double Helix.

Problems with DNA • Mutations: permanent changes in our DNA code – If occur in gametes, can be passed on to offspring. Mutagens: factors that can cause mutation, such as UV radiation, chemicals, etc. -these affect somatic cells only and cannot be passed on to offspring

Problems with DNA • Cancer: uncontrolled growth of cells that forms tumors – Can be caused by mutations – Carcinogens: cause cancer