DNA

DNA is Deoxyribo Nucleic Acid. DNA is a chemical. DNA is responsible for the production of proteins within a cell. Proteins are the `doers’ and `builders’ of your body – so by controlling the proteins, DNA controls the way your body looks and the way it functions.

DNA molecules are found in the nucleus of every cell in your body. The DNA in each cell carries the blueprint for making all the proteins in your body. However, cells in your body are usually specialised so they do not need to make all the possible proteins. This means your cells usually use only parts of the to make the proteins they need.

Structure of DNA

·  Double helix structure – like a twisted ladder.

·  The ladder uprights are made of a chain of alternating sugar and phosphate units. They provide support to the rungs of the “ladder” and do not provide any genetic code.

·  The “ladder’s” rungs are made of pairs of special molecules called nitrogen bases. There are only 4 different base units:

A = adenosine

T = thymine

C = cytosine

G = guanine

·  Each rung is a pair of bases. A is always paired to T, but the rung can be AT or TA. C is always paired with G, but the rung can be CG or GC. A and T are said to be complementary bases, as are C and G

2. (A) DNA Terminology

A section of a DNA molecule which provides codes for a certain trait is called a gene. A single strand of DNA may have 1000’s of genes along its length. A chromosome is simply a strand of DNA. A cell will have several or many chromosomes Chromosomes are actually quite long so they are “folded up” on themselves four times (called quaternary folding) to fit in the nucleus of the cell.

Humans have 46 chromosomes. 23 chromosomes are received from each parent – thus two very important points about your DNA are obvious.

•  Your DNA is a 50% combination of your dad’s DNA and 50% of your Mum’s DNA..

•  Each chromosome from your parent (each one of the 23) has a matching chromosome from the other parent. You don’t have 46 different chromosomes – you have 23 pairs of chromosomes. Each one of the pairs of chromosomes will be virtually identical – so there are two copies of each gene. This is very useful because if one copy of a gene does not work, you will have a backup copy which hopefully will make the correct protein.