Discussion of all aspects of cellular structure, physiology and communication.
Passive transport : transport 'something' done by cells without consuming ATP.
How they work? ahh...come on man..there're so many things to write then....
Q: Why are chemists great for solving problems?
A: They have all the solutions.
Just think of as if you were swimming down a stream. It would be passive transport because it does not take much energy for you to go down with current. Facilitated diffusion is a form of passive transport, when something hydrophilic needs to go down a concentration gradient in a phospholipid bilayer it uses a transport protein to help it, since inside the bilayer is hydrophobic. This is like you using a kayak to go down a stream. Active transport would be like you trying to swim against the current.
"In omnias paratus!"
The passive transport is a process of diffusion of molecules through the membrane. It is always produced in favour of gradient. Types of passive transport:
- Simple diffusion: Little molecules pass in favour of gradient but they can pass literally through the lipidic bilayer or by canal proteins. Examples: Transport of lipidic molecules (as steroidic hormones), anaesthetics as ether, liposoluble chemicals, apolar substances (as atmospheric oxygen and nitrogen) and some polar molecules (as carbon dioxide, ethanol, glycerin, etc). Also water pass by simple diffusion (it pass by canal proteins called aquoporines) by osmosis.
- Simple diffusion by regulated canal proteins: It is carried out by regulated canal proteins. Of this form, ions (as Na+, K+, Ca2+ and Cl-) come into the cell. Regulated canal proteins are proteins with a hole or internal canal which its opening is regulated by molecular signals (hormones, neurotransmissors, etc). The molecular signal joins to a certain region of the cell (its specific receptor) to activate the opening of the canal. When the molecular signal is joined with the receptor, the receptor suffers a structural change and the canal is opened.
- Facilitated diffusion: It allows the transport of little polar molecules as amino acids, monosaccharides, etc. As they can't pass through the lipidic bilayer, they require transmembranal proteins to pass into the cell. These transmembranal proteins are called permeases. When the molecule which is going to be transported joins to the permease, this protein suffers a conformational change and the molecule is pulled along into the cell.
Last edited by Enzyme on Sun Jan 22, 2006 3:43 pm, edited 1 time in total.
1. Simple diffusion (literally through the lipidic bilayer).
2. Simple diffusion (by canal proteins).
3. Facilitated diffusion.
4. Active transport.
Last edited by Enzyme on Sun Jan 22, 2006 3:43 pm, edited 2 times in total.
Two diagrams about simple difussion by regulated canal proteins.
Last edited by Enzyme on Sun Jan 22, 2006 3:44 pm, edited 1 time in total.
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