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CELL PROCESS LECTURE16 CLASS NOTES FOR BIOMEDICAL SCIENCE (BIOSCI 107)
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CELL PROCESS LECTURE16 CLASS NOTES FOR BIOMEDICAL SCIENCE (BIOSCI 107)
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CELL PROCESS LECTURE16 CLASSNOTES FOR BIOMEDICAL SCIENCE
(BIOSCI 107)
Biology for Biomedical Science (BIOSCI 107)
Professor Hassan
, 1. The difference between passive and active transport of solutes.
2. The difference between channel and carrier mediated transport.
3. Differentiate between primary and secondary active transport.
4. The properties driving water movement across cell membranes.
Substances cross membranes by a variety of processes:
(because the membrane has differing permeability to differing
molecules)
●Non-mediated transport does not directly use a transport
protein. (because the molecules are permeable across the
hydrophobic core of the lipid bilayer). ●Mediated transport
moves materials with the help of a
transport protein.
●Mediated transport can be
● Passive transport moves substances down their
concentration or electrochemical gradients with only their
kinetic energy.
●Active transport uses (input of) energy to drive substances against their concentration (glucose,or
amino acids) or electrochemical gradients (ions).
● Vesicular transport moves materials across membranes in small vesicles either by exocytosis or
endocytosis.
● Non-mediated transport: diffusion through the lipid bilayer
● Is always passive diffusion (no transport proteins), because the hydrophobic core of thebilayer does
not impose a barrier to the movement of the molecule.
● Important for absorption of nutrients and excretion of wastes.
● Molecules have to be soluble in the lipid bilayer and can interact with the hydrophobic coreof the
lipid bilayer so they are nonpolar, hydrophobic molecules are transported across the membrane
simply.
● E.g.oxygen, carbon dioxide, nitrogen, fatty acids, steroids, small alcohols, ammonia andfat-soluble
vitamins (A, E, D and K).
● Diffusion through ion channels
●Ion channels are pore-forming transmembrane proteins that
allow ions to pass through the channel pore. ● They are water-
filled tunnels that allow only ions of a certain size and/or charge
to pass through.
● The channel forms a water filled pore that shields theions from
the hydrophobic core of the lipid bilayer. ● Ions do not bind to
channel pore. Therefore transport is very rapid
● Properties of channels:ionic selectivity:
● Specific amino acids lining the pore determine the selectivity of thechannel to ions
● By being selective to a particular ion the channel can harness theenergy stored in the different ion
gradients
Gating:
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