Cell Cycle Overview

InterphaseG1

• Most variable in time length

• Cell growth; critical checkpoint

S

• Cell growth

• DNA replication

G2

• Final growth and preparation

M (mitotic) Phase=

Mitosis +

Cytokinesis

CytokinesisAnimal Cell vs. Plant Cell

Prokaryote Division• Binary Fission

• No nucleus= no mitosis

• Asexual reproduction

• Circular chromosome

Cell Cycle Regulation

Checkpoints

• Rely on kinases- enzymes that activate or inactivate other proteins by phosphorylation

• Kinase is always present, but usually inactive (becomes active when attached to cyclin)

• Called cyclin dependent kinase (Cdk)

G1 Checkpoint

• AKA “restriction point”

• If cell passes here, cell cycle will complete

• If cell stops here, cell moves to G0

• Cell specializes then dies (apoptosis)

• Ex. mature nerve and muscle cells

• Cancer cells never recognize checkpoint!

G2 checkpoint

• Used to indicate when to start M phase

• CDK + cyclin = MPF (maturation promoting factor)

• Build-up of MPF causes progression into M phase

• Too much MPF breaks down cyclin, inactivating MPF (negative feedback loop)

Cyclin Dependent Kinase

Cancer Cells• Ignore checkpoints

• Ignore density inhibition

• Lack specialization

• Often produce telomerase

• Travel/metastasize

• Are immortal!