Cell cycle and cell death

Prophase

Chromosomes condensed, nuclear envelope broken down, microtubules emerge from centrosome

Pro-metaphase

Microtubules attached to condensed chromosomes, Centrosomes moved towards opposite poles

Metaphase

Chromatids line up at the center and attached to microtubules

Anaphase

Chromatids pulled to opposite poles, Cell size elongated

Telophase

Chromatids surrounded by new nuclear envelope, Microtubules broken down

Cytokinesis

Cell cytoplasm splits into two identical daughter cell

G1

Cell monitors itself and the environment

S

DNA is replicated

G2

Cell prepares to divide, synthesis of tubulin

G0

Cells from heart or nerves may leave cell cycle after mitosis and never divide again

Analysis of Cell Cycle

Cells stained with fluorescent dye bound with DNA to show amount of DNA in the cell

M checkpoint

Checks if chromosomes are aligned or if there is an odd number of chromosomes

Cyclin-dependent kinases (CDK)

Triggers cell cycle by phosphorylating certain proteins on serine and threonine residues

Cyclins

Bind to cdk to control phosphorylation

Mitotic cyclins

Bind to cdk during G2 → required for entry to mitosis

G1 cyclins

Bind to cdk molecules during G1 → required for entry to S

Cell senescence

Dividing cells reach a limit and enter G0 forever

Necrosis

Cells die as a result of acute injury (passive)

Necrosis process

Cell swells and bursts → spills intracellular contents → causes inflammatory response

Apoptosis

Programmed cell death

Apoptosis process

Cell shrinks, cytoskeleton collapses, nuclear membrane disassembles, DNA breaks into fragments

Fate of dead cell

Engulfed by macrophage to recycle its contents

Caspases

Enzymes that cleave their target proteins at specific aspartic acids

Procaspases

Inactive form of caspases

Initiator caspase

Activates executioner caspases

Executioner caspases

cleavage of cytosolic protein and nuclear lamin

Extracellular activation of apoptosis

Fas ligand binds to death receptor → activates procaspase-8

Intracellular activation of apoptosis

Injured mitochondria releases cytochrome c to cytosol → binds to Apaf-1 (adaptor protein) → activates procaspase-9