DNA

​

DNA is a long chemical structure that determines our genetic code. Chromosomes are long threads of DNA coiled up in the nucleus of a cell.

 

Each chromosome contains hundreds of genes — instructions for building proteins. For example, you may have a gene for eye colour, hair colour, etc.

 

In body cells, chromosomes come in pairs. A typical adult has 23 pairs.

​

 

Mitosis and the Cell Cycle  

​

Cells divide to grow, repair, or replace old cells.  

There are three types of division you need to know for the exam:  

  ◦ Mitosis - forms two identical daughter cells (growth/repair)  

  ◦ Binary fission - like mitosis but for bacteria instead (no nucleus involved)

  ◦ Meiosis - forms sex cells like a sperm or egg (see Topic 4.6)

 

Mitosis Steps:  

1. Cell grows and copies organelles (ribosomes, mitochondria)  

2. DNA duplicates - each chromosome makes an identical copy  

3. Chromosomes line up and are pulled apart to opposite ends  

4. Nucleus splits  

5. Cytoplasm and membrane divide → two identical daughter cells. They then grow into adult cells.