Membrane Transport

Passive Transport

Transport across biological membranes that does not require chemical energy (ATP). (simple, osmosis, and facilitated)

Rate of Diffusion Factors

Affected by molecular size/mass, temperature, solution density, and concentration gradient.

Molecular Size and Diffusion

The smaller the molecule or ion, the faster the diffusion.

Temperature and Diffusion

The higher the temperature, the faster the diffusion.

Solution Density and Diffusion

The higher the density of the medium, the slower the diffusion.

Concentration Gradient and Diffusion

The greater the concentration gradient, the more rapidly a substance diffuses.

Osmosis

The diffusion of water across membranes from hypotonic to hypertonic environments.

Aquaporins

Specialized channel proteins that allow for the fast diffusion of water across cell membranes.

Carrier Proteins

Proteins that aid passive diffusion by binding polar, larger molecules like sugars and amino acids.

Active Transport

Movement of substances against their concentration gradient using energy and a transporter protein.

Primary Active Transport

Active transport that involves the direct hydrolysis of ATP.

Secondary Active Transport

Transport that indirectly uses ATP via an ion concentration gradient established by primary active transport.

Sodium-Potassium Pump

An example of primary active transport that moves Na+ out of and K+ into a neuron.

Sodium-Glucose Symporter

An example of secondary active transport used for glucose absorption in the intestine.

Vesicular Transport

The transport of large substances across membranes via endocytosis and exocytosis.

Phagocytosis

Cellular eating where a phagosome fuses with a lysosome for digestion.

Pinocytosis

Cellular drinking that brings fluids and dissolved substances into the cell.

Receptor-Mediated Endocytosis

Highly specific endocytosis utilizing coated pits with surface receptors underlined by clathrin.

Exocytosis

Vesicular transport used for secretion and waste removal.

Simple Diffusion

small molecules pass through phospholipid bilayer of the membrane, lipid soluble (hydrophobic): glycerol, ethanol, high to low

Facilitated diffusion

diffusion aided by protein channels or carriers, high to low concentration

Ligand gated channel

ligand binding causes conformational change that allows substance to pass

voltage gated channels

respond to change in membrane potential

uniporters

calcium binding protein in ER of a muscle cell actively transport Ca into ER from cytosol after muscle contraction, one at a time

Symporter

Sodium-glucose symporter in the intestine serves in glucose absorption, two at the same time

Antiporter

Sodium-potassium pump moves Na out of a neuron and K into the neuron, in and out simultaneously

Coated Pits

region on the membrane containing surface receptor proteins specific for certain molecules; underlined oncytoplasmic side by other proteins (clathrin)