Cell Cycle Cell Cycle Cell proliferation Cell division

Cell Cycle

Cell Cycle • Cell proliferation • Cell division is unique to eukaryotes

Binary Fission Origin of replication E. coli cell Two copies of origin Origin

Functions of Cell Division • Reproduction – Ex. amoeba • Growth & development - embryo • Renewal & repair -bone marrow cells Sand dollar embryo Bone marrow cells

– Distributes identical genetic material 2 daughter cells

• Two main stages: ▫ Interphase - Gap 0 (GO) - Gap 1 (G 1) - S (synthesis) phase - Gap 2 (G 2) ▫ M phase - Mitosis - Cytokinesis

What happens in Cell Division 0. 5 µm Before cell division Chromosome duplication (including DNA synthesis) Centromere Duplicated chromosome Separation of sister chromatids Sister chromatids Chromosome distribution Figure 12. 4 Centromeres Sister chromatids

Interphase • RNA & protein synthesis & growth • 20 -22 hours (mammalian tissue)

Gap 0 • cell leaves the cycle & quits dividing • temporary resting period or more permanent • Example: mature neurons, muscle cells

Gap 1 phase • Cells grow in size and do their ‘job’ • preparation for S phase • G 1 Checkpoint (control mechanism) • 5 -6 hours

G 0 G 1 checkpoint G 1 (a) If a cell receives a go-ahead signal at the G 1 checkpoint, the cell continues on in the cell cycle. G 1 (b) If a cell does not receive a go-ahead signal at the G 1 checkpoint, the cell exits the cell cycle and goes into G 0, a nondividing state.

S phase • DNA replication occurs • Cell grows more • 10 -12 hours

Gap 2 phase • cell grows & organelles replicate • preparation for mitosis • 5 -6 hours • G 2 Checkpoint

Experiments showed… S S G 1 M S M G 1 M

Cell Cyle Control System M G 1 S M G 2 G 1 S G 2 MPF activity • Cyclin-dependent kinases ▫ Constant Cyclin Time • Cyclin ▫ fluctuates G 1 S Cdk Cyclin is degraded 2 G Degraded Cyclin M • MPF (Mitosis-promoting factor) ▫ Triggers mitosis ▫ Destroys cyclin G 2 checkpoint MPF Cdk Cyclin M

Intermission Number!

Mitosis Waltz by: Moxy Frvous [In thick German accents] If it's ze secrets of life that you seek Zen srough (through) a mi-croscop you must peek! Mendel did vonders just using his eye, But to really see, you must magnify You can't help but notice ve're nossing (nothing) but cells, But vhere in ze cell does heredity dvell? The Nu-cleus! That's vhere it hides. You don't see much until it divides, Then Chro-masomes enter new phases, Split into two, und zat is ze basis Of Sexual Transmission vhich olvays engrosses Our feverish minds, but it's only Meiosis. Reducing zee chromasomes fifty percent, So vhen egg and sperm meet at zat blessed event, Ze Chro-masomes form one full set. Just two of each kind, zat's ze best! And that new cell begins to grow, Multiplies into an Em-bryo. Ze ex-plana-tion of zis growth Is it's due to a process ve know as Mitosis! And zat's vhat our Microscopes helped us determine, In Germany, vhere un ze germ cells are German!