KEY CONCEPT Cells have distinct phases of growth, reproduction, and normal functions.

Cell cycle Cell has a “life cycle” Brand new cell cell grows & matures to divide again cell grows & matures to never divide again G1, S, G2, M liver cells G1G0 epithelial cells, blood cells, stem cells brain / nerve cells muscle cells

The cell cycle has four main stages. The cell cycle is a regular pattern of growth, DNA replication, and cell division.

The main stages of the cell cycle are gap 1, synthesis, gap 2, and mitosis. Gap 1 (G1): cell growth and normal functions DNA synthesis (S): copies DNA Gap 2 (G2): additional growth Mitosis (M): includes division of the cell nucleus (mitosis) and division of the cell cytoplasm (cytokinesis) Mitosis occurs only if the cell is large enough and the DNA undamaged.

Cells divide at different rates. The rate of cell division varies with the need for those types of cells. Some cells are unlikely to divide (G0).

Cell size is limited. Volume increases faster than surface area.

Surface area must allow for adequate exchange of materials. Cell growth is coordinated with division. Cells that must be large have unique shapes.

KEY CONCEPT Cells divide during mitosis and cytokinesis.

Chromosomes condense at the start of mitosis. DNA wraps around proteins (histones) that condense it. DNA double helix DNA and histones Chromatin Supercoiled DNA

DNA plus proteins is called chromatin. chromatid telomere centromere One half of a duplicated chromosome is a chromatid. Sister chromatids are held together at the centromere. Telomeres protect DNA and do not include genes. Condensed, duplicated chromosome

Prophase

Centrioles move to opposite poles of cell green = key features Prophase Chromatin condenses visible chromosomes chromatids Centrioles move to opposite poles of cell animal cell Protein fibers cross cell to form mitotic spindle microtubules actin, myosin coordinates movement of chromosomes Nucleolus disappears Nuclear membrane breaks down

Transition to Metaphase green = key features Transition to Metaphase Prometaphase spindle fibers attach to centromeres creating kinetochores microtubules attach at kinetochores connect centromeres to centrioles chromosomes begin moving

Metaphase chromosomes line up in the middle of the cell.

Chromosomes align along middle of cell green = key features Metaphase Chromosomes align along middle of cell metaphase plate meta = middle spindle fibers coordinate movement helps to ensure chromosomes separate properly so each new nucleus receives only 1 copy of each chromosome

Anaphase sister chromatids separate to opposite sides of the cell.

Sister chromatids separate at kinetochores green = key features Anaphase Sister chromatids separate at kinetochores move to opposite poles pulled at centromeres pulled by motor proteins “walking”along microtubules actin, myosin increased production of ATP by mitochondria Poles move farther apart polar microtubules lengthen

Separation of chromatids In anaphase, proteins holding together sister chromatids are inactivated separate to become individual chromosomes 1 chromosome 2 chromatids 2 chromosomes single-stranded double-stranded

microtubule shortens by dismantling at kinetochore (chromosome) end Chromosome movement Kinetochores use motor proteins that “walk” chromosome along attached microtubule microtubule shortens by dismantling at kinetochore (chromosome) end Microtubules are NOT reeled in to centrioles like line on a fishing rod. The motor proteins walk along the microtubule like little hanging robots on a clothes line. In dividing animal cells, non-kinetochore microtubules are responsible for elongating the whole cell during anaphase, readying fro cytokinesis

Telophase the new nuclei form and chromosomes begin to uncoil.

Chromosomes arrive at opposite poles green = key features Telophase Chromosomes arrive at opposite poles daughter nuclei form nucleoli form chromosomes disperse no longer visible under light microscope Spindle fibers disperse Cytokinesis begins cell division

Cytokinesis differs in animal and plant cells. In animal cells, the membrane pinches closed. In plant cells, a cell plate forms.

Mitosis in animal cells