Cell DivisionCell divides into two daughter cells

Revised 10-09-2006

Cell CycleG1 phase

•Cellular Growth •Development

S phase •DNA Replication •Protein synthesis

G2 phase •Synthesis of organelles •Materials for cell division

M Phase•Mitosis

Length of the Cell Cycle

• Intestine•24-48 hours

• Frog embryo•1 hour

Control of the Cell Cycle

• Cyclins

• Cyclin Dependent Kinases

Cell Cycle Regulation

The cyclins are named “cyclins”

because their appearance during the cell cycle is cyclical

Cyclins/Kinases Complexes

G1 phase Cellular Growth and Development

Cyclin DCDK4CDK6

Cyclin ECDK 2

Checkpoint 1•Cell size?•DNA?

Cyclin D

cyclin D-dependent kinase Cdk6

S phase DNA Replication and Protein synthesis

Cyclin ACDK 2

Cyclin A

• Residues 173-432• 2 similar domains• Cyclin fold

–5 α-helices

CDK 2• Domain 1

–85 residues

–1 α-helix

–5 stranded β-sheet

• Domain 2

–213 residues

–α-helices

Cyclin A/CDK 2 Complex

Cyclin A/CDK 2 Complex

Inactive Active

G2

• Cyclin B

Checkpoint 2•All DNA Duplicated? •Cell size?•All DNA Intact?•Repair DNA

Cell Cycle RegulationM-phase promoting Factor MPF

Checkpoint 3•Chromosomes attached to spindle fibers?

Mitosis

.• Process by which the nucleus of

the cell is divided into two nuclei, each with the same number and kinds of chromosomes as the parent cell.

• Cytokinesis is the process by which the cytoplasm is divided.

Chromosomes

ProphaseLongest (50 - 60%)

• Appearance of chromosomes• Nucleolus disappears• Nuclear membrane breaks down• Centrioles separate and migrate to

opposite poles of cell

MetaphaseShortest

• Chromosomes line up across center of cell

• Spindle fibers form from centrioles to centromere

Anaphase

• Sister Chromatids split at Centromere

• Individual Chromosomes move toward poles

TelophaseFinal Phase

• Spindle fibers breakdown• Chromosomes uncoil into Chromatin• Nuclear envelope reforms• Nucleolus becomes visible

Mitosis in Whitefish and Onion

PROPHASE METAPHASE ANAPHASE TELOPHASE

Cytokinesis

The process by which the cytoplasm divides, forming two new cells.

Cytokinesis

• Animals •Cell membrane •pinches inward

• Plants•Cell plate

The process by which the cytoplasm divides, forming two new cells.

Result of Cell Division

Two cells that are identical to each other.