6.1. CELL CYCLE Flashcards
What is the cell cycle?
highly ordered sequence of events that takes place in a cell, resulting in division of the cell, and the formation of two genetically identically daughter cells
What are the main phases of the cell cycle?
interphase
mitotic phase (mitosis and cytokinesis)
Why do cells spend the majority of their time in interphase?
cells do not divide continuously, long periods of growth and normal working separate divisions.
What is interphase often referred to as and why is this inaccurate?
Resting phase as cells are not actively dividing, however interphase is actually very active
- cell is carrying out all of its major functions such as producing enzymes/ hormones, whilst also preparing for cell division
What happens 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
- normal metabolic processes of cells occur
What are the three stages of interphase?
G1
S
G2
What happens in G1 phase?
- first growth phase
- proteins from which organelles are synthesised are produced and organelles replicate
- cell increases in size
What happens in S phase?
- sythesis phase
- DNA is replicated in the nucleus
What happens in G2 phase?
- second growth phase
- cell continues to increase in size, energy stores are increased and duplicated DNA is checked for errors
Summarise what happens in mitosis:
- nucleus divides
Summarise what happens in cytokinesis:
- cytoplasm divides and two cells are produced
What is G0 phase in interphase?
- name given to the phase when the cell leaves the cycle, either temporarily or permanently
Why would cells enter G0 phase?
- differentiation
- DNA may be damaged
- too many cells in your body (could lead to age related diseases such as cancer/ arthritis)
What types of cells that enter G0 phase can re-enter the cell cycle?
- e.g. lymphocytes (white blood cells) in an immune response
What are checkpoints in the cell cycle?
- controls mechanisms
- monitor and verify whether the processes at each phase of the cell cycle have been accurately completed before the cell is allowed to progress into the next phase.
What are the checkpoints in the cell cycle?
- G1 checkpoint
- G2 checkpoint
- spindle assembly checkpoint
What does the G1 checkpoint check for?
- cell size
- nutrients
- growth factors
- DNA damage
Where is the G1 checkpoint?
- end of G1 phase, before entry to S phase
- if cell does not meet requirements, enters G0 phase
What does the G2 checkpoint check for?
- cell size
- DNA replication
- DNA damage
Where is the G2 checkpoint?
- end of G2 phase, before start of mitotic phase.
- if checkpoint is passed, cell initiates molecular processes that signal the beginning of mitosis
What does the spindle assembly checkpoint check for?
- chromosome attachment to spindle
Where is the spindle assembly checkpoint?
- point in mitosis where all chromosomes should be attached to spindles and have aligned
- mitosis cannot proceed unless this checkpoint is passed
What is the spindle assembly checkpoint also called?
- metaphase chackpoint
What brings about the passing of a cell cycle checkpoint?
kinases
What are kinases?
enzymes that catalyse the addition of a phosphate group to a protein
- this is called PHOSPHORYLATION
What does phosphorylation do?
- changes the tertiary structure of checkpoint proteins, activating them at certain points in the cell cycle
How are kinases activated?
- by binding to a variety of checkpoint proteins called cyclins
What does binding of the correct cyclin to the appropriate kinase form?
- cyclin-dependent kinase (CDK) complex
- these complexes are activated by enzymes
What happens to cyclins when they are not needed?
enzymes break them down
- this signals a cell to move on to the next stage of the cell cycle
What is cancer?
- group of many different diseases caused by uncontrolled division of cells
What is a tumour?
- abnormal mass of cells
What are the two types of tumours?
- benign (stop growing, don’t travel to different places in the body)
- malignant (grows uncontrolled/ unchecked, leads to cancer)
What are tumours the result of?
- damage or spontaneous mutation of genes that encode proteins that are involved in regulating the cell cycle
- including the checkpoint proteins
What is an example of a tumour in the cell cycle?
- if overexpression of a cyclin gene results from mutation, abnormally large quantity of cyclins would disrupt the regulation of the cell cycle
- resulting in uncontrolled cell division and tumour formation
- possibly leading to cancer
How can cyclin-dependent kinases be used in the treatment of cancer?
- used as a possible target for chemical inhibitors
- if activity of CDK’s can be reduced, may reduce/ stop cell division and therefore cancer formation
