Topic 1b - Cell Division

DNA - Deoxyribonucleic Acid; the genetic material in all organisms (except some viruses).

Gene - A section of DNA that codes for a particular protein.

Chromosomes - Thread-like structures which contain DNA. 

Humans have 46 in the body cells, 23 in the gametes.

Growth and DNA replication

1. When a cell isn't dividing, the DNA is spread out into long strands.

2. Before it divides, the cells grows and has to increase the amount of structures like: mitochrondrion and ribosomes.

3. It duplicates the DNA; 1 copy for each new cell. It's copied and forms chromosomes in the shape on an 'X'. Each side of the chromosome is an exact copy of the other.

1. The cell prepares to divide. You can't see the chromosomes at this stage. The DNA is replicated.

2. The chromosomes become visible and pair up.

3. The chromosomes are arranged in the middle of the cell. The spindle fibre forms.

4. The identical copies of each chromosome are pulled apart by the spindle fibre and move to the opposite ends of the cells.

5. The 2 nuclei form around the chromosomes. New cell membranes then form and two 2 new cells have been made. Each cell is identical to the original and has the same number of chromosomes.

Prophase

Metaphase

Anaphase

Telophase

A mnemonic to remember Please Make A Trifle

Mitosis must occur in the body as it be used for repairing cells, for overall growth and for producing diploid cells (a cell that contains 2 sets of chromosomes).