Bio CH 12

• No cell cycle control
• Divide excessively, invade other tissues
• -Growth factor depletion does not stop division
• -No density-dependent inhibition
• Cells divide indefinitely (with nutrients)
• -HeLa immortal cell line is 59 years old

• Regular rate of cell division is controlled by:
• Internal cues-anaphase delayed until all chromosomes attatched
• External cues (ex- growth factor) protein released by cells stimulates other cells to divide. Density dependent inhibition prevents crowded cells from dividing. Cultured cells divide to form single layer, then stop. Anchorage dependence allows many cells to be attatched to substrate to divide and may be effect of plasma membrane proteins.

• Cells divide without mitosis. Single bacterial chromosome replicates.
• No miotic spindle formation which is how chromosomes separate is not clear. Plasma membrane pinches off cells and grows inward, new cell wall deposited.

• NO cleavage furrow (semi-rigid cell wall present)
• Cell plate forms in middle of cell
• -Golgi vesicles come together to create cell plate (organized by microtubels)
• plate enlarges and fuses with plasma membrane
• New cell wall forms along cell plate.

• Animals:
• Occurs by cleavage furrow
• contractile ring of actin microfilaments
• Cleavage furrow is tightened
• Parent cell is pinched in two (result: daughter)
• Cytoplasm is split between daughter cells

• In Mitosis, Chromatin coils tightly, chromosomes condense. (Chromosomes sister chromatids visible)
• Mitotic spindle begins to form (centrosomes move apart, microtubles extend)

In mitosis, nuclear envelope disinegrates. Centrosomes move to poles (microtubles join w/ chromosomes at kinetochore)

• –Chromosomes align at “metaphase plate”
• •Aligned in a plane in the middle of the cell
• –Kinetochores of sister chromatids attached to microtubules from opposite poles

• kinetochore microtubules shorten
• chromatids separate and move o each pole
• -chromatids can now be called chromosomes
• cell elongates
• -nonkinetochore microtubles lengthen

• MITOSIS!
• daughter nuclei form at the two poles
• -nuclear envelopes develop
• chromatin becomes less tightly coiled (diffuses)
• -eventually chromosomes no longer visible

• G2(Interphase)
• nuclear envelope intact
• chromosomes and centrosome already duplicated

• **Interphase is longest portion of cycle
• 1)G1 phase: first gap with cell growth
• 2)S phase: DNA synthesis (chromosomes duplicated)
• 3)G2 phase: cell growth and preparation for Miotic phase

• Protein organizes DNA (ex. histones)
• chromatin: DNA-protein complex
• ---chromatin duplicates prior to division
• -----Chromatin condenses during division
• --------Makes chromosomes short, thick, visible
• ----------Densely coiled/folded

• Somatic cells (produced by mitosis)
• all cells of organisms oher than reproductive cells2 sets of chromosomes (2n or diploid)
• 46 chromosomes (2n=46)
• Gametes (produced by meiosis)
• preproductive cells: sperm and egg
• 1 set of chromosomes (1n or haploid)
• 23 chromosomes (n=23)

• Prokaryotic genome
• -single DNA melecule/cell
• Eukaryotic genome
• multiple DNA molecules/cell
• DNA molecules packaged into chromosomes
• 1 chromosome=1DNA molecule
• Every eukaryotic species has a certain number