Biology Part 3

Chromosomes are really long molecules of DNA

1)DNA stands for Deoxyribose Nucleic Acid

2)It contains all of the instructions to put an organism together and make it work.

3) Its found in the nucleus of animals and plant cells in really long molecules called chromosomes.

A gene codes for a specific protein.

1) A gene is a section of DNA

2) Cells make proteins by stringing amino acids together in a particular order.

3)Only 20 amino acids are used, but they make up thousands of different proteins.

4) Genes tell cells in what order to put amino acids together

5) DNA also determines what proteins the cell produces

6) Which determines what type of cell it is.

DNA is unique apart from identicle twins and clones.

DNA finger printing is a way of cutting up a person's DNA into smal sections and then seperating them. Every person genetic fingerprint has a unique pattern

Mitosis makes new cells for growth and repair.

Body cells normally have 2 copies of each chromosome. One from the organisms mother and one from its father. When a body cells divides it needs to make new cells identicle to the original cell- with the same number of chromosomes. This type of cell division is called mitosis. It is used when plants and animals want to grow or to replace cells that are damaged.

For diagram and order of what to do look at page 27 in the science revision guide ( AQA)

1) During sexual reproduction 2 cells called gametes combine to form a new individual.

2)Gametes only have one copy of each chromosome, they combine when they meet

3) Human body cells have 46 chromosomes. The gametes have 23 each

Meiosis involves 2 divisions- To make new cells which only have half the original chromosomes, cells divide by meiosis. In humans, it onlly happens in the reproductive organs.

See diagram on page 28 of the revision guide for detailed explination ( AQA)