9.3: The eukaryotic cell cycle is regulated by a molecular control system Flashcards
Why does the frequency of cell division differ from each cell
due to regulation at a molecular(within the cell)
What is the cell cycle driven by
The cell cycle is driven by specific signaling molecules present in the cytoplasm
Where is evidence of cytoplasmic signals drawn from
When 2 cells were fused together, Cytoplasmic signals from one of the fused cells could cause the nucleus from the second cell to enter the same stage of the cell cycle as the first cell
cell cycle control system
an operating set of molecules in the cell that both triggers and coordinates key events in the cell cycle controls the cell cycle
checkpoints
the cell cycle is a control point where stop and go-ahead signals can regulate the cycle
cyclins
(1)proteins that regulate the cell at a molecular level by a set of regulatory proteins and protein complexes, you have different fluctuations of these
CDKS(Cyclin-dependent kinases)
(2)type of protein kinase that regulates the cell at a molecular level, are inactive until they bind with cyclins and then are called MPFs
What goes on in the G1 checkpoint
known as the restriction point, the G1 checkpoint seems to be the most important checkpoint, If a cell receives a go-ahead signal at the G1 checkpoint, it will usually complete the S, G2, and M phases, monitored by cyclin-CDK complexes
G0 phase
if the go-ahead signal is not received in G1, the cell goes into this phase where it is in a nondividing state(like the muscle and nerve cells) but can be called back from this phase(liver cells)
MPF(maturation-promoting factor)
cyclin-Cdk complex(attached together) that triggers a cell’s passage past the G2 checkpoint and into the M phase
Explain the G2 checkpoint
critical MPF levels are required in order to go onto the M phase, this is incase error occurs in chromsomes
Explain the fluctuations in MPF, Cyclins, and CDKs through the cell cycle
The MPF and cyclins are low until right up until the M checkpoint, the CDKs are constant through the whole thing
Explain the degradation of cyclin
CDK is constant until a cyclin attaches around the G2 phase starting, then the cyclin degrades and breaks at the end of the M phase
M checkpoint, what happens?
A stop signal is received if any of the chromosomes are not attached to a microtubule.
Explain one example of internal signals
M phase checkpoint has an internal signal where the anaphase does not begin until the chromosomes are all attached to microtubules
Explain one example of external signals
growth factors tell certain cells to divide
What is the significance of PDGF in terms of growth factors
PDGF is needed to secrete a growth factor or else the cells will not divide, they also let you pass the G1 phase
what checkpoint do most cells not get past
G1 because most cells just go to G0
density-dependent inhibition
where crowded cells stop dividing and if there is a vacancy of cells, cells divide until it is filled
anchorage dependence
where the cells need to be attached to something in order to divide
what makes cancer cells so rapid growth-wise
Cancer cells have neither density-dependent inhibition nor anchorage dependence, they do not respond to signals
How do cancer cells divide?
They make their own growth factors or divide without the signal itself due to a faulty cell cycle control system
transformation
where the normal cell becomes a cancerous cell
how are tumors formed
when cancer cells are not eliminated by apoptosis, tumors are masses in otherwise healthy tissues
Benign tumor
if abnormal cells remain only at the original sits, is the lump, not bad
Malignant tumors
invade surrounding tissues and can metastasize, where the cells export more cancerous cells to other parts of the body where additional tumors form
2 types of cancer therapy
High energy radiation damages DNA in cancer cells and even more DNA in normal cells and Chemotherapeutic drugs interfere with not only cancer cell division, but also normal cell division
Why is cancer so hard to treat
cancer is unique to the person, cancer is very complex
What are the 3 molecules that control the cell cycle
CDK, Cyclins, MPF
Why does cyclin fluctuate
Cyclins are constantly degrading
What molecule moves the cell cycle
MPF
