Chapter 7: Membrane Structure and Function

3 Questions
- What is selective permeability function?
This is a plasma membranes that allows some substances to cross it more easily than others.
- What is amphipatic?
It is some molecule that has both hydrophilic region and hydrophobic region.
- What is passive transport?
Passive transport is the diffusion of a substance across a biological membrane.
5 Main Facts
- The plasma membrane is the edge of life, the boundary that separates the living cell from its surroundings.
- A membrane is held together primarily by hydrophobic interactions, which are much weaker than covalent bonds.
- Phospholipids form the main fabric of the membrane, but proteins determine most of the membrane's functions.
- Integral proteins penetrate the hydrophobic core of the lipid bilayer.
- Peripheral proteins are appendages loosely bound to the surface of the membrane, often to exposed parts of integral proteins.

Diagram

Water moves from an area of higher to lower free water concentration(lower to higher solute concentration). Two sugar solutions of different concentrations and separated by a membrane, which the solvent can pass through but the solute cannot. water molecules move randomly and may cross in either direction, but overall, water diffuses from the solution with less concentrated solute to that with more concentrated solute. This transport of water, or osmosis, equalizes the sugar concentrations of both sides.

Summary
Chapter 7 talked about how cellular membranes control the passage of substances. Cellular membranes are fluid mosaics of lipids and proteins. Molecules have a type of energy called thermal motion. One example of thermal motion is diffusion, the movement of molecules of any substance so that they spread out evenly into the available space.
The diffusion across a membrane is called passive transport because the cell does not have to expand energy to make it happen. Another type of transport is osmosis which the water across a selectively permeable membrane.

Video
http://www.youtube.com/watch?v=sdiJtDRJQEc

10 Key Terms:
- Diffusion: the movement of molecules of any substance so that they spread out evenly into the available space.
- Passive transport: the diffusion of a substance across a biological membrane.
- Osmosis: the diffusion of water across a selectively permeable membrane.
- Tonicity: the ability of a solution to cause a cell to gain or lose water.
- Isotonic: referring to a solution that, when surrounding the cell, has no effect on the passage of water into or out of the cell.
- Hypertonic: referring to a solution that, when surrounding the cell, will cause the cell to lose water.
- Osmoregulation: regulation of solute concentrations and water balance a cell or organism.
- Active transport: the movement of a substance across a cell membrane, with an expenditure of energy, against its concentration or electrochemical gradient; mediated by specific transport proteins.
- Electrogenic pump: a transport protein that generates voltage across a membrane.
- Endocytosis: cellular uptake of biological molecules and particulate matter via formation of new vesicles from the plasma membrane.