1. Lecture 35 Normal Cell Cycle Ozgur Unal
NIS - BIOLOGY
Lecture 35
Normal Cell Cycle
Ozgur Unal

2. Traffic Lights Why are there traffic lights on heavy intersections?
How would the traffic flow without the traffic lights?

3. Normal Cell Cycle Traffic light regulates the flow of traffic.
Similarly, in a cell, the cell cycle is regulated.
The cell cycle in eukaryotic cells is driven by a combination of two substances that signal the cellular reproduction processes: Cyclins and Cyclin-dependent kinases (CDKs)
Cyclins are proteins.
Cyclins bind to enzymes
called CDKs.

4. Normal Cell Cycle
Cyclins/CDKs start the various activities that take place in the cell cycle during interphase and mitosis.
Different Cyclin/CDK combinations control different activities at different stages of the cell cycle.
Example: In G1, the combination of Cyclin with CDK signals the start of the cell cycle.
The same cyclin/CDK combination
also signals the end of the cell cycle.

5. Normal Cell Cycle
The cell cycle has built-in checkpoints that monitor the cycle and can stop it if something goes wrong.
Example: A checkpoint near the end of the G1 stage monitors for DNA damage and can stop the cycle before entering the S stage of interphase.
There are also other checkpoints.
Check out Figure 9.11