it is phosopholipid bilayer : hydrophilic head and hydrophobic tail connects to the another opposite of hydrophobic tail.
Q. what are the two major population of membrane proteins?
integral proteins and peripheral proteins
Q. what is the diffusion of a substance across a biological membrane without expend energy to make it happen?
passive transport
5 facts
1. membrane is made of phospolipid and there are some intergral proteins.
2. the intergral proteins do trasnport, enzymatic activity, signal transduction, cell-cell recognition , intercellular joining and attachment to the cytoskeleton and extracellular matrix.
3. hypertonic will lose water to its environment because it has low concentration.
4. hypotonic will enter water the cell faster tan it leaves, because it has high concentration
5. there are three types of endocytosis, phagocytosis, pinocytosis and receptor-mediated endocytosis.
diagram - cell membrane
cell membrane is made of two phospholipid are connected its tail to tail , so that the hydrophilic head are far away each other. there are also a lot of intergral proteins which transfer or function many things for the cell.
10 key terms
1.Amphipathic : having both a hydrophilic region and a hydrophobic region.
2.Fluid mosaic model, the membrane is a fluid structure with a “mosaic” of various proteins embedded in or attached to a double later of phospholipids.
3.Intergral proteins is one of the two major populations of membrane proteins, which penetrate the hydrophopic core of the lipid bilayer, many are trasnmembrane proteins, which span the membrane; other integral proteins extend only partway into the hydrophobic core.
4.Peripheral proteins are not embedded in the lipid bilayer at all; they are appendages loosely bound to the surface of the membrane, often to exposed pars of integral proteins.
5.Glycolipid: membrane carbohydrates are usually short, branched chains of fewer than 15 sugar units, some are covalently bonded to lipids.
6.Transport protein hydrophilic substances can avoid contact with the lipid bilater by passing through it that span the membrane.
7.Diffusion: molecules have a type of energy called thermal motion. One result of thermal motion, the movement of molecules of any substance so that they spread out evenly into the available space.
8.Osmosis : the diffusion of water across a selectively permeable membrane; the movement of water across cell membranes and the balance of water between the cell and its environment are crucial to organisms.
9.Tonicity, the ability of a solution to cause a cell to gain or lose water. The tonicity of a solution depends in part on its concentration of solutes that cannot cross the membrane, relative to that inside the cell.
10.Facilitated diffusion : many polar molecules and ions impeded by the lipid bilayer of the membrane diffuse passively with the help of transport proteins that span the membrane.
video - diffusion
http://www.youtube.com/watch?v=VUnvwrx8Wq4
summary
membrane is basically made of phospholipid bilayer with cross section and intergral proteins in it. The protein works a lot of things such as transporting, enzymatic activity, signal transduction, cell-cell recognition , intercellular joining and attachment to the cytoskeleton and extracellular matrix. some of them requires ATP to work on but some of them are not extending energy to do. especially the cell-cell reconition is important that they will have different carbohydrates to distinguish from other cell.
because of the formation of lipid bilayer, the molecules are not easily entering and exiting randomly, they need some certain condition to get into a cell, such as nonpolar molecule, small molecule. but the proteins built into the membrane play key roles in regulating transport.
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