2.6.1(Cell cycle)

State all the phases of the cell cycle

• M phase

• G0 Phase

• G1 Phase - growth phase

• S Phase

• G2 Phase

State the 3 main checkpoints in the cell cycle

• G1/S Checkpoint

• G2/M Checkpoint

• Metaphase Checkpoint

Give 2 reasons for checkpoints in the cell cycle

• To prevent uncontrolled division that would lead to tumours

• To detect and repair damage to DNA

State an example of the causes of DNA damage

• UV light

State the reason for the cell cycle’s events happening in a specific order

• So the cycle cannot be reversed

• The DNA only duplicates once during each phase

Describe the M phase and the events which occur in the cell during this phase

• Cell growth stops in the M Phase

• Mitosis occurs

• Cytokinesis occurs

Describe the G1 Phase and the events which occur in the cell during this phase

• The growth Phase of the interphase:

  • Cells grow and increase in size

  • Transcription pf genes to make RNA occurs

  • Organelles duplicate which DNA does not

  • Biosynthesis occurs

Describe the G0 Phase and the events that occur in the cell during this phase

• Resting phase:

  • This phase only occurs if the cell doesn’t pass the G1 checkpoint

  • Cells may undergo apoptosis, differentiation, or senescence

  • Some types of cells remain in the phase for a very long time or forever

Describe the S phase and the events that occur in the cell during this phase

• Synthesis phase:

  • Once the cell has entered this phase, it is committed to completing the cell cycle

  • DNA replicates

  • When all chromosomes have been duplicated, each one consists of pair of identical sister chromatids

Describe the G2 Phase and the events that occur in the cell during this phase

• Special chemicals ensure that the cell is ready for mitosis by stimulating proteins that will be involved in making chromosomes condense and in formation of spindle

• The cell grows during this phase

Describe the events that occur during the G1/S Checkpoint

• At the end of the G1 phase, the cell is checked if it is the correct size, has enough nutrients and growth factors, and that DNA is not damaged before the S phase

Describe the events that occur during the G2/M Checkpoint

• At the end of the G2 Phase, DNA replication, DNA damage and cell size are all checked before going to the M phase

Describe the events that occur during the Metaphase checkpoint

• A Chemical triggers condensation of chromatin

• Halfway through the cycle, the metaphase checkpoint ensures that the chromosomes are attached to spindle fibres so the nucleus can undergo mitosis correctly