Day 2 - Section 3

What ensures irreversibility in the cell cycle

Protein destruction via the ubiquitin-proteasome system

What is the ubiquitin-proteasome system

A system that tags proteins for degradation and destroys them

What are the steps of protein destruction in the ubiquitin-proteasome system

Ubiquitin tagging recognition by proteasome and degradation

What is APC/C

Anaphase Promoting Complex or Cyclosome that targets proteins for destruction

What activates APC/C

M-Cdk activity

What is the main target of APC/C during mitosis

Cyclin B

What happens when APC/C tags Cyclin B

Cyclin B is degraded

What is the effect of Cyclin B degradation

M-Cdk activity decreases

What type of feedback is created by M-Cdk activating APC/C

Negative feedback

What is the key logic of this feedback loop

M-Cdk activates APC/C which destroys Cyclin B which shuts off M-Cdk

Why is this negative feedback important

It ensures exit from mitosis

Why does the cell use destruction instead of inhibition

Destruction is permanent while inhibition is reversible

What would happen if only inhibition were used

The cell could reverse cell cycle progression

What does protein destruction guarantee

Irreversible progression through the cell cycl