Cell Division and Regulation of the Cell Cycle

Chromosomes Made of DNA (which carries coded genetic information) and proteins Each organism has a certain number Humans have 46 Not visible until division because it is spread throughout the nucleus During division, they condense Prior to condensing, they replicate, so they consist of sister chromatids with centromeres near the center

Cell Cycle A series of events during which the cell grows, prepares for division, and divides to form two daughter cells G1, S, G2, M phases Interphase – cell growth, synthesis of organelles and proteins, DNA replication Mitosis – the division of the cell nucleus

Mitosis Prophase – chromosomes condense and centrioles separate, spindle forms, nuclear envelope breaks down Metaphase – chromosomes line up across the center of the cell Anaphase – sister chromatids separate Telophase – chromosomes unravel, nuclear envelope reforms around new nuclei of daughter cells

Cytokinesis The division of the cytoplasm In animals – cells pinch apart into nearly equal halves In plants – a cell plate (then a cell wall) forms

Controls and Regulators Cells that come in contact with other cells stop dividing Cyclins are proteins that regulate the cell cycle Two kinds of regulators Internal – proteins that respond to events in the cell External – proteins that respond to events outside the cell

Uncontrolled Cell Growth Cancer – a disorder in which some of the body’s own cells lose the ability to control growth Do not respond to regulators Form tumors that can damage surrounding tissues Control over cell cycle has been broken down