Lecture3_MCDB_20.pdf

Lecture3_MCDB_20.pdf - Lecture 3 -Eukaryotic Cell Structure...

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Lecture 3 -Eukaryotic Cell Structure -Cellular Energy Eukaryotic vs. Prokaryotic cells Plasma Membranes in all cells: essentially the same structure and function Separate the cytoplasm from environment critical function of Membrane Transport Two types of passive transport: 1. Diffusion 2. Osmosis Passive transport is the spontaneous diffusion of molecules across a membrane. Diffusion and Concentration Gradients Passive transport always DOWN energy (concentration) gradient Simple vs. Facilitated Diffusion ! Most molecules can’t get through plasma membranes on their own. ! require Carrier molecules Transport proteins Defects in Transport Proteins ! Can reduce or even bring facilitated diffusion to a complete stop ! Serious health consequences ! Many genetic diseases Cystinuria and kidney stones ! The diffusion of water across a membrane is a special type of passive transport called OSMOSIS . ! adding solutes lowers [water] ! Water molecules move across the membrane until the concentration of water inside and outside of the cell is equalized.
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Cells in Solution ! Tonicity the relative concentration of solutes outside of the cell relative to inside the cell Hypertonic Hypotonic Isotonic Osmosis is the passive diffusion of water across a membrane. The Direction of Osmosis ! Determined only by a difference in total concentration of all the molecules dissolved in the water ! It does not matter what solutes they are. How do laxatives relieve constipation? ! Milk of magnesia and magnesium salts ! Water moves via osmosis from the cells into the intestines. ! Moving molecules against a concentration gradient requires energy. ! called Active transport ! Proteins embedded within the plasma membrane act like motorized revolving doors to actively transport the molecules. Two distinct types of active transport: 1. Primary 2. Secondary (differ only in the source of the fuel) Primary active transport: uses energy directly from ATP Secondary Active Transport ! An indirect method many transporter proteins use for fueling their activities ! The transport protein simultaneously moves one molecule against its concentration gradient while letting another Fow down its concentration gradient.
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! No ATP is used directly. ! But, at some other point and in some other location, energy from ATP is usually needed to pump one of the types of molecules involved against their concentration gradient. ! exceptions: acidophiles, halophiles Endocytosis and exocytosis are used for bulk transport of particles. Many molecules are just too big to get into a cell by passive or active transport. Three types of endocytosis: 1. Phagocytosis 2. Pinocytosis 3. Receptor-mediated endocytosis Phagocytes: -white blood cells -“eat” bacteria Pinocytosis : the process of cells taking in dissolved particles and liquid Faulty cell membranes are a primary cause of cardiovascular disease. What modi±cation to them might be
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Lecture3_MCDB_20.pdf - Lecture 3 -Eukaryotic Cell Structure...

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