Cell Division and Regulation of the Cell Cycle

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 � G 1, S, G 2, 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