Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Cell Growth and Division Why do cells divide? DNA “Overload” – Not enough information for a big cell Exchanging Materials – Must be able to obtain nutrients and eliminate wastes easily Ratio of Surface Area to Volume – Volume increases faster than the surface area Surface Area vs. Volume Chromosomes DNA and proteins Each chromosome consists of two identical sister chromatids Centromeres – area where the chromatids are attached The Cell Cycle Series of events that cells go through as they grow and divide 4 phases – M phase (mitosis and cytokinesis) – the division of the nucleus and the cell – G1 phase (the first “gap”) – cells increase in size and synthesize new proteins and organelles – S phase (synthesis of DNA) – the chromosomes are replicated – G2 phase (the second “gap”) – many of the organelles and molecules needed for mitosis are produced The Cell Cycle The Cell Cycle Interphase – G1 + S + G2 M phase – Prophase – Metaphase – Anaphase – Telophase – Cytokinesis Mitosis Interphase Cell spends most of its time in interphase Cell grows Carrying out basic cell functions Making organelles Copying chromosomes Prophase Nucleoli disappear Chromatin condenses (becomes shorter & thicker) Chromosomes become visible Centrioles separate & move to opposite poles Spindle fibers form between the centrioles Nuclear membrane disappears Metaphase Chromosomes attach to the spindle fibers at the centromere Chromosomes align at the equator Anaphase Centromeres split apart Chromatids separate & move apart Sister chromatids are pulled to opposite poles Telophase Cell membrane pinches together at the equator Nucleoli reappear Nuclear membrane encloses each set of chromosomes Chromosomes loosen up Cytokinesis Division of the cytoplasm Begins during telophase Cell membrane continues pinching until it separates forming 2 daughter cells 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 Cycle Regulators Cyclin – a protein which regulates the cell cycle – Cyclins bind to enzymes called cyclindependent kinases – Different cyclin/CDK combinations control different activities 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 – Part of the checkpoint process 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 – Cells no longer respond to the control mechanisms – Occurs due to mutations in the DNA – Cancer cells crowd out normal cells, resulting in loss of tissue function Tumor – cluster of cancer cells Carcinogens – cancer causing substances Cancer Apoptosis Programmed cell death Occurs when: – Webbing between human fingers and toes disappears before birth – Leaves fall from trees Also occurs in cells with DNA damage to prevent cancerous growths Stem Cells Unspecialized cells that can become specialized under certain conditions Embryonic stem cells – unspecialized cells from an embryo – Can develop into a wide variety of specialized cells Adult stem cells – found in certain types of tissues – Might be able to develop into different types of cells