Study Guide Week 3

Study Guide Week 3 - TA: Victoria Ha Email: viha@ucsd.edu...

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TA: Victoria Ha Section: (B03) Monday 5:00-5:50pm Solis 111 Email: viha@ucsd.edu Office Hours: Thursday Hi Thai 2-3pm Study Guide Week 3 Disclaimer: These notes are intended for you to supplement your studies. They are by no means a substitute for going to lecture!! Pages 131-136 in textbook 8 th Edition MEMBRANE TRANSPORTATION All cell membranes have a phospholipids bilayer membrane The cell membrane is composed of a hydrophilic (polar) head, a hydrophobic (non-polar) tail, and proteins that are interspersed through the membrane Diffusion : random movement of molecules of any substance so that they spread out evenly into the available space. in the absence of other forces, a substance will diffuse from HIGH concentration LOW concentration. In other words it will diffuse down its concentration gradient : the region along which the density of a chemical substance decreases. There is NO ENERGY INPUT. *Note: a substance goes down its concentration gradient and is not affected by other substances. Substances that can diffuse through bilyar: nonpolar/small molecules (i.e hydrocarbons, carbon dioxide, oxygen) molecules. Substances that can NOT diffuse through bilayer: polar/ large molecules (i.e glucose and water) these molecules pass through lipid bilayer very slowly and does not cross very rapidly. Therefore they need a transporter protein to cross. Passive Transport : diffusion of a substance across a biological membrane with no expenditure of energy. Facilitated Transport : the spontaneous passage of molecules or ions across a biological membrane with the assistance of specific transmembrane transport protein. This is mainly for many polar molecules and ions impeded by the lipid bilayer that cannot diffuse passively.
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TA: Victoria Ha Section: (B03) Monday 5:00-5:50pm Solis 111 Email: viha@ucsd.edu Office Hours: Thursday Hi Thai 2-3pm Transport Proteins: a transmembrane protein that helps a specific substance or class of closely related substances to cross the membrane. A) Channel proteins : protein that has hydrophilic channel that certain molecules use as a tunnel through the membrane. (It’s pretty much a hole in the cell membrane that certain molecules can pass through) 1) “Leak” channels : always open 2) Gated channels: open or close in response to a stimuli 3) Aquaporins: the passage of water molecules through the membrane. B) Transporters: has a binding site for one or more molecules. Proteins bind to the molecule and when the molecule is bound, the transporter changes conformation and transports the molecules into the cell. Active Transport: movement of substances against its concentration gradient. Goes from LOW concentration to HIGH concentration. Needs energy (ATP).
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TA: Victoria Ha Section: (B03) Monday 5:00-5:50pm Solis 111 Email: viha@ucsd.edu Office Hours: Thursday Hi Thai 2-3pm An example of this is the sodium potassium pump. The Na+/K+ pump must break ATP down to ADP in order to pump three ions of sodium outside the cell, while it
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Study Guide Week 3 - TA: Victoria Ha Email: viha@ucsd.edu...

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