4.6-4.7: Regulation Of The Cell Cycle Flashcards
Throughout the cell cycle, there are checkpoints. What are checkpoints? (2)
- control points that regulate the cell cycle
- cells receive stop/go signals
What are the major checkpoints?
G1, G2, M (spindle)
What is the most important checkpoint?
G1
What happens in the G1 checkpoint?
- checks for cell size, growth factors, and DNA damage
What are the Stop and Go signals of the G1 checkpoint?
Go - cell completes the whole cell cycle
Stop - cell enters a non-dividing (quiescent) state known as G0 phase
As stated in the G1 checkpoint, the stop signal is that the cell renters a non-dividing state known as G0 phase. What happens to these cells? (2)
- some cells stay in G0 forever (muscle/nerve cells)
- some cells can be called back into the cell cycle
What does the G2 checkpoint check for?
- checks for completion of DNA replication and DNA damage
What are the Stop and Go signals of the G2 Checkpoint?
Go - cell proceeds to mitosis
Stop - cell cycle stops and the cell will attempt to repair damage
— if damaged cannot be repaired, the cell will undergo apoptosis
What does the M (spindle) checkpoint check for?
- checks for microtubule attachment to chromosomes at the kinetochores at metaphase
What are the stop and go signals of M checkpoint?
Go - cell proceeds to anaphase and completes mitosis
Stop - cell will pause mitosis to allow for spindles to finish attaching to chromosomes
What does the regulation of the cell cycle (internally) involve? (3)
Involves an internal control system that consisted of:
- proteins known as cyclin
- enzymes known as cyclin - dependent kinases
What are cyclins? (3)
- proteins
- concentration varies (fluctuates)
- cyclins are synthesized and degraded at specific stages of the cell cycle
What are cyclin - dependent kinases (CDK)? (3)
- concentration is constant through each phase of the cell cycle
- varying levels of Different Cylyns in each stage
- active ONLY when it’s specific cyclin is present
Each cyclin-CDK complex has a specific regulatory effect. How?
- Active CDK Complexes phosphorylate target proteins, which help regulate key events in the cell cycle
What are 3 external cell cycle regulators?
- Growth factors
- Contact (or density) inhibition
- Anchorage dependence
What are growth factors and what do they do? (3)
- Hormones released by cells that stimulate cell growth
2. Signal transduction pathway is initiated - CDKs are activated leading to progression through the cell cycle
What is contact (or density) inhibition? (2)
- cell surface receptors recognize contact with other cells
- initiates signal transduction pathway that stops the cell cycle in G1 phase
What is anchorage dependence?
- cells rely on attachment to other cells or the extracellular matrix to divide
How can normal cells be cancerous and why? (2)
- Through DNA mutations
- DNA mutations change the DNA
How many mutations on average do cancer cells accumulate?
- 60 or more on genes that regulate cell growth
What does a normal cell do in a cell cycle? Ex. What do they follow, divide, die? (3)
- follow checkpoints
- divide on average 20-50 times in culture (in petri dishes)
- go trough apoptosis when there are significant errors
What do cancers cells do in a cycle? (3)
- do not follow checkpoints
- divide infinitely when in culture (considered to be immortal)
- evade apoptosis and continue dividing with errors
How do cancer cells evade apoptosis?
- they have telomeres that do not degrade and therefore never get the signal for apoptosis
The uncontrollable growth of cancer cells can lead to a ______. What is it? (2)
- tumour
- a mass of tissue formed by abnormal cells
