AP Biology Crosby High School Mitosis AP Biology Crosby High School

Cell Division Reproduction, Growth, and Repair Basic steps: Duplicates DNA Copies split to opposite ends Cell splits 2 Daughter Cells formed

Genome Prokaryote vs. Eukaryote Prokaryote: Single strand of DNA More than on strand of DNA Each species has a specific number of chromosomes Human Somatic Cells: 46 chromosomes (Diploid) Human Gametic Cells: 23 chromosomes (Haploid)

Structures and Overview of Splitting DNA strand wrapped around proteins Chromatin: DNA/Protein complex Condenses to form Chromosomes Copied forming Sister Chromatids Chromatids joined at Centromere Chromatids separate in Mitosis Cytoplasm separates in Cytokinesis

Interphase 90% of Cell Cycle Consists of Three Phases G1 Phase (Gap one) Growth of the cell S Phase (Synthesis) DNA replication G2 Phase (Gap two)

Mitotic Phase “Please Pour Me Another Tequila” Prophase Prometaphase Anaphase Telephase

Mitotic Spindle Centrosomes form spindles Centriole pairs inside Centrosomes Centrosomes replicate near nucleus Two centrosomes grow spindle microtubules Separate to opposite ends of the cell Spindles “play tug-o-war” at Kinetochores Pull both directions until chromosomes reach metaphase plate

Mitotic Spindles and Anaphase Proteins holding sister chromatids deactivate Chromosomes “walk” along microtubules Microtubules shorten by depolymerizing Nonkinetochore microtubules lengthen the cell

Cytokinesis Begins with Cleavage furrow Actin and Myosin contraction Differences of Plant Cytokinesis Vesicles from Golgi form cell plate Plate grows and fuses with plasma membrane Cell wall materials accumulate and form cell wall

Mitosis: Evolution of Binary Fission? Prokaryotes have no spindle fibers Origin of Replication replicates in opposite directions Plasma membrane grows inward Dinoflagellates and Diatoms Unicellular algae Divides with nuclear envelope intact

Cell Cycle Regulation Controlled on the molecular level by signals Fused cells could force Mitosis Fused to have two nuclei Performed same function Cell cycle control system Internal signals External signals

Cell Cycle Checkpoints 3 major checkpoints G1(Restriction point) Begins the S phase Decides whether the cell will divide or not Yes: Enters S phase No: Enters G0 phase G2 Precedes mitosis M Has mitosis completed?

Cyclin and Cyclin Dependent Kinases Fluctuates in the cell When present bind to Cdks for activation G1 checkpoint contains 3 Cdks and several cyclins Maturation Promoting Factor (MPF) Past G2 Initiates Mitosis by phosphorylating proteins Turns itself off by degrading cyclin Remains present in inactive form

Internal Signals Messages received from Kinetochores Anaphase does not begin until all kinetochores are attached to a spindle fiber Signal comes from non-attached Anaphase promoting complex (APC) inactive Active: APC triggers breakdown of cyclin and deactivation of sister chromatids

External Signal Platelet-derived Growth Factor (PDGF) Fibroblasts have PDGF receptors Heals wounds Density dependent Inhibition Cells form one layer IN CULTURE and stop Continue to grow when cells are removed Anchorage Dependence Must be attached to substratum

Cancer Uncontrolled cell growth Control point malfunctions Cell continues to grow beyond inhibition HeLa cells have been growing since 1951

Onset of Cancer Transformation: cell malfunctions If not destroyed it becomes a tumor Benign: Remains at origin Malignant: invasive enough to impair organs Cells lose function and inhibition Cells lose attachment and spread Spread through lymphatic or blood vessels Metastasis

Cancer

Mitosis

Mitosis (cont.)

Spindle Shortening

Cyclin and MPF