Cell Cycle
Key Terms:
Cell Cycle: Highly ordered sequence of events which takes place inside a cell, resulting in its division.
Mitosis: Division of the nucleus into two identical daughter cells.
Cytokinesis: The cytoplasm divides and two cells are produced.
Checkpoint: a control mechanism of the cell, at the end of each phase, which checks if the processes in the phase have been completed correctly.
Interphase:
- Long period of growth and cell regulation.
- Not actively dividing.
- DNA is replicated and checked for errors.
- Protein synthesis.
- Mitochondria grow and divide.
- Chloroplasts grow and divide.
- Normal metabolic processes occur.
- Three Stages:
- G1 (First growth phase), where proteins are synthesised, organelles replicate and the cell increases in size.
- S (Synthesis phase), where DNA is replicated in the nucleus.
- G2 (Second growth phase), where duplicated DNA is error checked, energy stores grow and cell size grows.
- Cell splits into two new cells.
- Mitosis - nuclear division.
- Cytokinesis - cytoplasm divides producing two new identical daughter cells.
- G0 is the phase in which the cell leaves the cycle.
- Can be temporary or permanent.
- Reasons for leaving the cell cycle include...
- Differentiation: where a cell specialises to a particular function and is no longer able to divide.
- DNA Damage: cell can no longer divide so leaves the cycle.
- Senescent Cells: Cells which cease to divide and leave the cell cycle. Most normal cells become senescent cells after a certain number of divisions.
Controlling the Cell Cycle:
- G1 Checkpoint. At the end of G1 phase. If all requirements are met, the cell enters S phase for DNA replication. If not, cell enters G0.
- Checks cell size
- Monitors nutrients levels
- Monitors growth factors
- Checks for DNA damage
- G2 Checkpoint. At the end of G2 phase. If all requirements are met, the cell begins mitosis.
- Checks for correct DNA replication
- Checks for DNA damage
- Checks cell size.
- Metaphase checkpoint (Spindle assembly checkpoint). If all requirements are met, mitosis continues.
- Checks that spindle fibres are attached to chromosomes.
- Passing of checkpoints is a result of the enzyme kinase bonding to cyclin, forminG a cyclin-dependant kinase complex (CDK).
- CDK complexes activate important cell cycle proteins by adding a phosphate group to proteins (phosphorylation) which changes the tertiary structure of checkpoint proteins, moving to the next stage of the cell cycle.
Download this unlabeled cell cycle diagram, then label the phases, checkpoints and their functions! | |
File Size: | 110 kb |
File Type: | jpg |
Cell Cycle Regulation and Cancer:
Key Terms
Cancers: a group of disases caused by uncontrolled division of cells.
Tumour: an abnormal mass of cells.
Benign Tumours: Harmless tumours which have stopped growing and do not migrate to other areas of the body.
Malignant Tumours: Harmful tumours which continue to grow and spread around the body.
- Malignant tumours are often the result of damage or mutation of genes which encode proteins that are involved in cell cycle regulation.
- CDK Complexes can be used as a target for chemical inhibitors in the treatment of cancer.
- By inhibiting CDK complexes, division may be stopped, and thus stopping cancer formation.