Cell Growth and Division

Why do cells divide? DNA “Overload” DNA “Overload” –Not enough information for a big cell Exchanging Materials Exchanging Materials –Must be able to obtain nutrients and eliminate wastes easily Ratio of Surface Area to Volume Ratio of Surface Area to Volume –Volume increases faster than the surface area

Surface Area vs. Volume

Chromosomes DNA and proteins DNA and proteins Each chromosome consists of two identical sister chromatids Each chromosome consists of two identical sister chromatids Centromeres – area where the chromatids are attached Centromeres – area where the chromatids are attached

The Cell Cycle Series of events that cells go through as they grow and divide Series of events that cells go through as they grow and divide 4 phases 4 phases –M phase (mitosis and cytokinesis) – the division of the nucleus and the cell –G 1 phase (the first “gap”) – cells increase in size and synthesize new proteins and organelles –S phase (synthesis of DNA) – the chromosomes are replicated –G 2 phase (the second “gap”) – many of the organelles and molecules needed for mitosis are produced

The Cell Cycle M phase G 2 phase S phase G 1 phase

The Cell Cycle Interphase – G 1 + S + G 2 Interphase – G 1 + S + G 2 M phase M phase –Prophase –Metaphase –Anaphase –Telophase –Cytokinesis Mitosis

Interphase Cell spends most of its time in interphase Cell spends most of its time in interphase Cell grows Cell grows Carrying out basic cell functions Carrying out basic cell functions Making organelles Making organelles Copying chromosomes Copying chromosomes

Prophase Nucleoli disappear Nucleoli disappear Chromatin condenses (becomes shorter & thicker) Chromatin condenses (becomes shorter & thicker) Chromosomes become visible Chromosomes become visible Centrioles separate & move to opposite poles Centrioles separate & move to opposite poles Spindle fibers form between the centrioles Spindle fibers form between the centrioles Nuclear membrane disappears Nuclear membrane disappears

Metaphase Chromosomes attach to the spindle fibers at the centromere Chromosomes attach to the spindle fibers at the centromere Chromosomes align at the equator Chromosomes align at the equator

Anaphase Centromeres split apart Centromeres split apart Chromatids separate & move apart Chromatids separate & move apart Sister chromatids are pulled to opposite poles Sister chromatids are pulled to opposite poles

Telophase Cell membrane pinches together at the equator Cell membrane pinches together at the equator Nucleoli reappear Nucleoli reappear Nuclear membrane encloses each set of chromosomes Nuclear membrane encloses each set of chromosomes Chromosomes loosen up Chromosomes loosen up

Cytokinesis Division of the cytoplasm Division of the cytoplasm Begins during telophase Begins during telophase Cell membrane continues pinching until it separates forming 2 daughter cells Cell membrane continues pinching until it separates forming 2 daughter cells Plant cells have a cell plate that forms Plant cells have a cell plate that forms

Videos…

Life Spans of Human Cells

Controls on Cell Division Cell-to-cell contact – when cells come in contact with other cells, they stop dividing Cell-to-cell contact – when cells come in contact with other cells, they stop dividing

Cell Cycle Regulators Cyclin – a protein which regulates the cell cycle Cyclin – a protein which regulates the cell cycle –Cyclins bind to enzymes called cyclin- dependent kinases –Different cyclin/CDK combinations control different activities throughout the cycle Quality control checkpoints occur throughout the cycle Quality control checkpoints occur throughout the cycle –If something goes wrong the cycle stops

Cell Cycle Regulation

Cell Cycle Regulators Internal regulators – proteins that respond to events inside the cell Internal regulators – proteins that respond to events inside the cell –Part of the checkpoint process External regulators – proteins that respond to events outside the cell (e.g. growth factors) External regulators – proteins that respond to events outside the cell (e.g. growth factors) –Direct cells to speed up or slow down the cell cycle

Uncontrolled Cell Growth Cancer – uncontrolled cell growth Cancer – uncontrolled cell growth –Cells no longer respond to the control mechanisms –Occurs due to mutations in the DNA Tumor – cluster of cancer cells Tumor – cluster of cancer cells Carcinogens – cancer causing substances Carcinogens – cancer causing substances