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Transcript
Why are cells so tiny? • Larger cells do not function as efficiently – The surface is the only way cells interact with the environment – Surface-area-to-volume ratio • As cell size increases, volume grows much more rapidly Cell radius (r) Surface area (4πr2) Volume ((4/3)πr3) 1 units 12.57 units2 4.189 units3 10 units 1,257 units2 4,189 units3 Cell Theory • Schleiden and Schwann • Three principles – All living things are composed of cells – Cells are the smallest living things (Functional units of the body) – Cells come from pre-existing cells • Prokaryotes Cell Types – Lack a nucleus and membrane bound organelles – MUCH smaller than eukaryotes – Bacteria • Eukaryotes – Have a nucleus and organelles – Much bigger than prokaryotes Cell Organelles • Cell membrane – Semi-permeable • Cytoplasm— “cell blood” – Fluid matrix surrounding nucleus – Surrounded by a cell membrane • Nucleus— “cell brain” – Contains chromatin (loosely coiled DNA) Endoplasmic reticulum • Interconnected membranes forming canals and flattened sac-like spaces • Functions: – Communications system – Rough ER: studded with ribosomes • Involved in protein synthesis – Smooth ER: has no ribosomes • Involved in synthesizing lipid Ribosomes • Composed of protein and RNA • May be free in the cytoplasm or attached to ER • Function: – Involved in protein synthesis Golgi apparatus • Stack of flattened membranes • Function: – Package and transports proteins from the cell Mitochondria • “Cell powerhouse” • Contains its own DNA – Capable of self-reproduction • Composed of 2 membranes • Contains enzymes used in cell respiration • Function: – Produce ATP for cellular energy (cell respiration) Lysosomes • Small sacs from the Golgi apparatus • Contains enzymes capable of breaking down breaking down nutrients or toxins • Function: – Digestion Centriole • Twin hollow cylinders (centrioles) • Function: – Involved in cell division Vesicles • Tiny sacs formed by the cell membrane folding in and pinching off • Function: – Intake or excretion of large materials (endocytosis and exocytosis) Microfilaments and Microtubules • Tiny rods usually arranged in meshes or bundles • Function: – Involved in cell movement – Provides structure to the cell Cillia and Flagella • Fine, long, threadlike organelles protruding from the cell surface • Function: – Cell movement centrosome Golgi lysosome apparatus vesicles nucleus mitochondria flagella smooth ER rough ER Cell Membrane • Selectively permeable (semi-permeable) – Allows some substances in, excludes others • Composed of phospholipid bilayer (containing cholesterol) and protein inclusions – Fat soluble molecules pass through the lipid part – Water soluble molecules must move through protein component • Pores, channels or receptors Passive Transport • Movement of a material into or out of a cell without the use of energy. – Diffusion – Osmosis – Facilitated diffusion – *** NO ENERGY REQUIRED*** Diffusion • The process by which molecules move down a concentration gradient – Move from area where there is more concentration to areas that are less concentrated – Rate limited by concentration Facilitated Diffusion • Diffusion using special carrier molecules to allow usually non-permeable molecules to pass through a selectively permeable membrane – Example: Insulin facilitates glucose movement • Rate of passage is limited by the number of carrier molecules and concentration Osmosis • The diffusion of water through a selectively permeable membrane which may not allow dissolved substances to pass • May result in changing volumes on either side of the membrane • Osmotic pressure – The amount of pressure needed to stop osmosis Concentration Types • Hypertonic – A solution which has a greater concentration of solute particles than a given cell or solution • Hypotonic – A solution which has a lesser concentration solute particles than a given cell or solution • Isotonic – A solution which has an identical concentration of solute particles to a given cell or solution Filtration • The forcing of permeable molecules through a membrane by hydrostatic pressure – Example: Blood pressure Active Transport • The movement of molecules against a concentration gradient using cellular energy and carrier molecules – Proton pump – Sodium-potassium pump ***ENERGY REQUIRED*** Bulk Passage • Endocytosis – The inward movement of molecules through a membrane by infolding and pinching off vesicles • Pinocytosis: taking in tiny droplets of liquid • Phagocytosis: taking in solid material • Receptor Mediated: molecule bonds with receptor protein • Exocytosis Cell division • Prokaryotes – Binary fision • DNA replicated in parent • Parent divides • Fast • Eukaryotes – Mitosis • Complicated • Lots of DNA – Form chromosomes (compact structures, composed of DNA and histone proteins, that can be manipulated easily during cell division Cell cycle • Interphase – Period “Inbetween” cell division – Majority of cell’s life • Cell growth • Protein synthesis Mitosis • Cell division that Is Mighty Common • Makes all cells EXCEPT gametes (reproductive cells) • DNA is doubled then – Cells divide once Prophase • Cells Prepares to divide • Chromatin condenses into chromosomes • Nuclear membrane disappears Metaphase • Chromosomes line up in the Middle • Spindle Apparatus stretches from pole to pole Anaphase • Sister chromatids move Away to opposite poles Telophase • Cell “Tears” in two • Nuclear membrane reforms • Chromosomes disperse into chromatin • Cytokinesis (cytoplasmic division) (separate phase?) – Produces 2 identical “daughter cells” Cell differentiation • Process by which cells develop different characteristics in structure and function • Differences in outcome – Directed by cell’s DNA – Determined by cell’s position in the body and its chemical environment