| Define cell cycle | The process that all body cells in multicellular organisms use to grow and divide |
| Explain the cell cycle process | Interphase, subdivided into 3 growth stages:
- gap phase 1 (G1) = cell grows and new organelles and proteins are made
- synthesis (S) = cell replicates its DNA ready to divide by mitosis
- gap phase 2 (G2) = cell keeps growing and proteins needed for cell division are made
- M phase = mitosis and cytokinesis |
| How is the cell cycle regulated | - G1 checkpoint = the cell checks that the chemicals needed for the replication are present and for any damage to the DNA before entering the S-phase
- G2 checkpoint = the cell checks whether all the DNA has been replicated without and damage. If it has, the cell can't enter mitosis
-Metaphase checkpoint = the cell checks that all the chromosomes are attached to the spindle before mitosis can continue |
| What are the main stages of mitosis | Interphase, prophase, metaphase, anaphase and telophase |
| Describe interphase | - Cell carries out normal function, but also prepares to divide.
- The cell's DNA is unravelled and replicated, to double it's genetic content
- organelles also replicate
- ATP content increases |
| Describe prophase | - chromosomes condense
- tiny bundles of protein called centrioles start moving to opposite ends of the cell, forming a network of protein fibres across it called the spindle
- the nuclear envelope breaks down and chromosomes lie free in the cytoplasm |
| Describe metaphase | - the chromosomes line up along the equator of the cell and become attached to the spindle by their centromere
- at the metaphase checkpoint, the cell checks that all the chromosomes are attached to the spindle before mitosis can continue |
| Describe anaphase | - the centromeres divide, separating each pair of sister chromatid
- the spindles contract, pulling chromatids to opposite poles of the cell |
| Describe telophase | - the chromatids reach the opposite poles of the spindle
- they uncoil and become long and thin and are called chromosomes again
- a nucleus envelope forms around each group of chromosomes, so there are now 2 nuclei
- 2 genetically identical cells are produced |
