MEMBRANE TRANSPORT

Because of _____ the lipid bilayer of the cell membranes restricts the passage of most polar molecules.

2 Major Membrane Proteins

Used by cells to evolve in order to ingest essential nutrients, excrete metabolic waste products, and regulate intracellular ion concentrations.

devote up to two-thirds of their metabolic energy to transport process.

undergo sequential conformational changes to transport specific small molecules across membranes

• form narrow pores • allows passive transmembrane movement primarily of water and small inorganic ions.

Solubility in oil

Cell membranes allow small nonpolar molecules to permeate by

inherited diseases that causes individuals’ cell cannot transport certain amino acids from either the urine or the intestine into the blood

• By forming a protein-lined pathway across the membrane, these proteins enable specific hydrophilic solute to cross the membrane without coming in direct contact with the hydrophobic interior of the lipid bilayer.

carriers of premeases

Cells use dedicated channel proteins to diffuse water across the lipid membrane

Impermeable to Ions

• Downhill • All channels and many transporters allow solutes to cross the membrane only passively

Drives passive transport and determines its direction

Influences the transport if the solute carries a net charge

The concentration gradient and the electrical gradient combine to form a net driving force

Transmembrane movement of small molecules mediated by transporters

Transmembrane movement of small molecules mediated by channels

compete for the same binding site and many or may not be transported

bind elsewhere and alter the structure of the transporter

3 main ways cells carry out active transport

harness the energy stored in concentration gradients to coupe the uphill transport of one solute across the membrane to the downhill transport of another

couple uphill transport to the hydrolysis of ATP