Chapter seven: membrane structure and function

Q1:what is plasma membrane's structure?
A1: phospholipid bilayer and protein.
Q2: what's plasma membrane's function?
Q2: controls traffic into and out of the cell it surrounds.
Q3: why does plasma membrane have that structure?
A3: cell membrane is a boundary the separates cell from its surrounding. it has hydrophobic layer outside so that it won't be dissolved in its surrounding. the mosaic protein help substances transport.

Five Facts:
1. cellular membrane are fluid mosaics of lipids and proteins
2. membrane structure results in selective permeability
3. passive transport is diffusion of a substance across a membrane with no energy investment
4. active transport uses energy to move solutes against their gradients
5. bulk transport across the plasma membrane occurs by exocytosis and endocytosis

Figure

mosaic proteins in phospholipids help select substances tranport. it has integral protein and peripheral protein. Because phospholipids are hydrophilic inside and hydrophobic outside, the hydrophobic part of protein is inside the lipids.

Summary:
The plasma mambrane is the edge of life, the boundary that separates the living cell from its surrounding. It exhibits selective permeability which allows some substances to cross it more easily than others. Lipids and protein are the staple ingredients of membrane. The phospholipids are amphipathic which has both hydrophobic and hydrophilic parts. In fluis mosaic model, the membraen is a fluid structure with mosaic proteins in bilayer. Membranes are not static, it can move laterally, flip-flop. Low temperature can cause unsaturates hydrocarbon tails. Cholesterol will also add to the membrane. Integral protein penetrate the hydrophobic core of th elipid bilayer. Peripheral proteins are appendages loosely bound to the surface of the membrane. Membrane carbohydrates are glycolipids or glycoproteins.
Cell membrane are permeable to apecific ions and a variety of polar molecules. Hydrophlic substances can avoid contact with the lipid bilayer by passing through transport proteins. The selective permeability of a membrane depends on both the discriminating barrier of the lipid bilayer and the specific transport proteins. Passive transport is the movement across membranes that does NOT require cellular energy.Diffusion is the net movement of atoms, ions or molecules down a concentration gradient. Osmosis is the diffusion of water.Tonicity is the concentration of water relative to a cell.Osmoregulation is the control of water balance.Facilitated diffusion has transport protein that helps materials through the cell. Active transport is movement across membranes that DOES require cellular energy. Electrogenic pump is a transport protein that generates voltages across a membrane.Sodium-potassium pump is themajor electrogenic pump of animals.Proton pump is the main electrogenic pump of plants, fungi, and bacteria.Exocytosis is the movement of bulk material out of cells.
Endocytosis is the movement of bulk materials into cells.

Key Term:

1. aquaporin-A channel protein in the plasma membrane of a plant, animal, or microorganism cell that specifically facilitates osmosis, the diffusion of water across the membrane.


2. concentration gradient-A region along which the density of a chemical substance increases or decreases


3. electrogenic pump-An ion transport protein that generates voltage across a membrane.


4. hypertonic-Referring to a solution that, when surrounding a cell, will cause the cell to lose water.


5. hypotonic-Referring to a solution that, when surrounding a cell, will cause the cell to take up water.


6. isotonic- Referring to a solution that, when surrounding a cell, has no effect on the passage of water into or out of the cell.


7. receptor-mediated endocytosis-The movement of specific molecules into a cell by the inward budding of membranous vesicles containing proteins with receptor sites specific to the molecules being taken in; enables a cell to acquire bulk quantities of specific substances.


8. tonicity-The ability of a solution surrounding a cell to cause that cell to gain or lose water.


9. turgid-Swollen or distended, as in plant cells. (A walled cell becomes turgid if it has a greater solute concentration than its surroundings, resulting in entry of water.)


10. ligand-A molecule that binds specifically to another molecule, usually a larger one.

Video:

http://www.youtube.com/watch?v=s0p1ztrbXPY