The cell cycle
- Created by: Freja
- Created on: 10-04-21 10:25
View mindmap
- The Cell Cycle
- Interphase
- Cells do not divide continuously and there are long periods of growth and normal working separate divisions
- A cell spends the majority of its time in this phase
- During interphase
- DNA is replicated and checked for errors in the nucleus
- protein synthesis occurs in the cytoplasm
- Mitochondria grow and divide, increasing in number in the cytoplasm
- Chloroplasts grow and divide in plant and algal cell cytoplasm, increasing in number
- The norml metabolic processes of cells occur
- In eukaryotic cells the cell cycle has two main stages- Interphase and Mitotic (division) phase
- The 3 main stages of interphase
- G1- The first growth phase: proteins from which organelles are synthesised are produced and organelles replicate. The cell increases in size.
- S- synthesis phase: DNA is replicated in the nucleus.
- G2- the second growth phase: the cell continues to increase in size, energy stores are increased and the duplicated DNA is checked for errors
- Mitotic Phase- the period of cell division
- Involves 2 stages: mitosis- the nucleus divides and cytokinesis- the cytoplasm divides and two cells are produced
- G0- is the phase where the cell leaves the cycle, either temporarily or permanently and there are a number of reasons for this.
- Differentiation- a cell that becomes specialised to carry out a particular function is no longer able to divide. It carries out the function indefinitely and not enter the cell cycle again
- The DNA of a cell may be damaged, so it is no longer viable. A damaged cell can no longer divide, so it enters a period of permanent cell arrest. The majority of normal cellsonly divide a limited number of times and become senescent.
- As you age, the number of cells in you body increases.
- Checkpoints
- The control mechanisms of the cell cycle, the replicated DNA is error free and the chromosomes are in the correct position
- They monitor and verify whether the processes at each phase of the cell cycle have been accurately completed
- It is vital to ensure a cell divides when it has grown to the right size
- Checkpoints occur at various stages
- G1 checkpoint- is at the end of the G1 phase, before the entry into the S phase.
- If the cell satisfies the requirements of the checkpoint it is triggered to begin DNA replication and if not it enters a resting state(G0)
- G2 checkpoint- at the end of the G2 phase, before the start of the mitotic phase.
- In order for this checkpoint to be passed, the cell has to check a number of factors, including if the DNA has been replicated without error. If the checkpoint is passed, the cell initiates the molecular processes that signal the beginning of mitosis
- Spindle assembly checkpoint (metaphase checkpoint)- at the metaphase point in mitosis
- Mitosis cannot proceed until this checkpoint is passed
- G1 checkpoint- is at the end of the G1 phase, before the entry into the S phase.
- Interphase
Comments
No comments have yet been made