Cell cycle

What are the stages in the interphase

1. G1: first growth phase cells grow in size, protein synthesis occurs and organelles duplicate. 46 chromosomes

2. S: synthesis phase. DNA us replicated and each chromosome is duplicated so now 92 chromosomes

3. G2: second growth phase cells grow in size, energy stores increase and replicated DNA checked

Why are there checkpoints within the cell cycle

• check for DNA damage

• ensure DNA has replicated accurately

• make sure the cell is large enough and has enough resources

• prevent uncontrolled cell division

If a cell does not meet this criteria then the cell enters G₀ phase

What is the G₀ phase

Cell has left the cell cycle due to error during cell cycle or cell has differentiated to perform a specialised function. Cells also enter this phase once they have replicated enough where they are senescent

Where do the checkpoints occur within the interphase

1. G1 checkpoint at end of G1 phase where cell size, nutrients, growth factors, DNA damage are checked

2. G2 checkpoint at end of G2 phase which checks whether DNA has replicated correctly and if there is DNA damage

What are kinases

• These control cell cycle check points as they catalyse the addition phosphate group to proteins which changes tertiary structure activating them

• In cell cycle these are called cyclin dependent kinase (CDKs) and to be activated need to be bound to cyclin. Once complex formed kinase is activated and can then phosphorylate, and activate, proteins required for the next stage of the cell cycle

How can targeting CDKs help stop cancer

A malignant tumour forms due to uncontrolled cell division perhaps due to mutation or damage. By inhibiting CDKs, they cannot activate the proteins needed for cell cycle progression so cell stuck and cannot enter another phase or mitosis so cell division is stopped