Everything on the GCSE Biology Mitosis & the Cell Cycle poster is written out below, section by section. Use it to search the sheet, copy parts into your own notes, or check a fact quickly.
Chromosomes
DNA in the nucleus is coiled up into long structures called chromosomes. Each chromosome carries many genes - sections of DNA that code for proteins. Body cells have chromosomes in pairs. Humans have 23 pairs (46 in total), one of each pair from each parent.
An X-shaped chromosome consists of two sister chromatids joined at a region called the centromere.
The Cell Cycle
Growth & DNA replication
The cell grows and the number of its subcellular structures (such as mitochondria and ribosomes) increases. DNA is then replicated so that each chromosome becomes two identical copies - two sister chromatids joined at a centromere.
Mitosis
- Each sister chromatid is pulled to opposite ends of the cell.
- The nucleus divides.
- The cytoplasm and cell membrane divide to form two identical daughter cells.
The Four Stages of Mitosis
1. Prophase - Chromosomes condense and become visible as X-shapes. The nuclear membrane breaks down.
2. Metaphase - Chromosomes line up across the centre of the cell.
3. Anaphase - Spindle fibres pull the sister chromatids of each chromosome to opposite ends of the cell.
4. Telophase - A new nuclear membrane forms around each set of chromosomes. The cytoplasm and cell membrane divide.
Why Mitosis Matters
Growth - Multicellular organisms grow from a single fertilised egg cell.
Repair & replacement - Mitosis replaces cells that have been damaged or worn out, for example skin cells and gut lining cells.
Asexual reproduction - In some organisms, offspring are produced by mitosis from one parent, for example plants reproducing via runners.