Biology of cultured cells conti-

Part 4By : Saib al owini

Cell proliferation

• Cell cycle • Cell cycle regulation • differentiation

• Interphase 95% of cell cycle• Organelle duplication, DNA replication, and

cell Growth

G1

• Metabolically active• Organelle duplication, but no DNA • Duration variable short in embryonic, cancer

cells• Prepares for S phase• Cells that remain in G1 for a long time = G0

(permanent tissues, such as neural tissue)

s

• Committed to cell division once this starts• DNA and centrosome replication

• two identical daughter genomes

G2

• Growth continues• Enzymes and proteins synthesized for cell

division

mitosis plus cytokinesis

• Mitosis: • Prophase• Metaphase• AnaphaseTelophas

Embryonic cells

• Cell growth not part of cell cycle• All energy goes into DNA synthesis• So G1 lacking and G2 quite short• Each round of division subdivides cytoplasm

into smaller and smaller cells, • Until adult cell size is reached

Cell cycle regulation

G1 check point

• Cyclin D • Sensitive to growth factors (rapidly degraded)• Cdk –cyclin D complex drives cell through G1

to S phase

Rb

• Key substrate of Cdk- cyclin D complex• Binds to transcription factor E2F• Growth factors- activated Cdk-Cyclin• Phosphorylates Rb• to Allows transcription to proceed• Rb gene: expresses Rb protein, acts as G1

brake

G2 check

• Function of G2 checkpoint:• error check: DNA replication must be

completed• Detects unreplicated DNA, holds cell at G2• Detects damaged DNA, arrests cell in G2 until

damage repaired

Mitotic Cdk-CyclinComplex (MPF) and G2

• Mpf • Controls G2 checkpoint by phosphorylating

proteins involved in early stages of mitosis

Regulation at Spindle Assembly Checkpoint

• Check for chromosome attachment to spindle • MPF causes activation of anaphas- promoting

complex• Complex pathway that promotes anaphase

p53: Tumor Suppressor gene

• DNA damage increased levels of p53 • p53 is a transcription factor activates gene coding

for p21• P21: P21: cdk inhibitor that arrests cells in G1

until damage repaired • If DNA repair not successful, p53 induces

apoptosis apoptosis• Called guardian of the genome • 50% of all cancers related to mutations of p53

control of proliferation

• Cells density • ( EGF,PDGF,FGF) • Contact inhibition• +VE OR NEGATIVE

Differentiation

• Maintenance : * interaction - collagen gell -cellulose -matrix glycoprotein * soluble inducer ( hydrocortisone,

retinoides) Without serum

Dedifferentiation , deadaptaion

• Proliferation • (or ) differentiation

How to prepare suitable condition for 1ry culture

• Ph • Buffers