Objective: Be able to predict what happens when cells from different phases are fused together. Explain the results of fusion of interphase and M cells with respect to cyclin and MPF
Start by looking at this image
In this experiment cells from G1 phase are fused with cells from M phase
The cells from M phase (at top) have gone through S, therefore they have sisters.
The cells from G1 phase have not gone through S, do they have not replicated.
They have just started to condense. You can see them (not typical of G1 chromosomes) but they are not as condensed as the ones above.
Objective distinguish the roles of cyclin and CDKs in promoting the cell cycle
Objective be able to interpret the cell fusion events in terms the functions of cylcin and CDK
Based on these results, researchers hypothesized the presence of a factor that induced M phase. Years of genetic and biochemical research showed that this something is a factor called cyclin. Cyclin is a protein that accumulates at particular cell cycle stages and then are destroyed. Different cyclins trigger different stages.
Cyclin B is responsible for mitosis
The key here is that cyclin by itself does not cause M phase. Instead, it activates an enzyme called CDK. CDK stands for cell division Kinase. A kinase is an enzyme that adds phosphate. When CDK adds phosphates to chromosomes, they condense. This enzyme is also responsible for other prophase events like formation of a spindle and breakdown of the nuclear membrane.
For cell division, recall that there is a checkpoint a the G1/S boundary. In order for cells to advance to S, they need proteins called growth factors. For example, if you injure yourself platelets (a type of blood cell most known for clotting) releases a protein called Platelet Derived Growth Factor. This protein stimulates cells to divide to replace the dead ones.
Here is a video about hair growth factors (sorry, it is an ad, but it gets the point across)
Reception In cell division, the growth factor binds to a receptor. Two common types are Enzyme linked and G-protein linked. Both play roles in cell division control.
Here is an example showing an enzyme linked receptor from Open Stax