Membrane Transport I

Vocabulary flashcards covering cellular membrane transport mechanisms, passive and active transport, osmosis, and diagnostic characteristics of transport proteins.

Passive transport

The movement of substances down their concentration gradient (from high to low concentration) without energy input from the cell.

Active transport

The movement of substances against their concentration gradient (from low to high concentration) using energy (ATP) from the cell.

Simple diffusion

The passive movement of hydrophobic (non-polar) solutes, such as gases ($O_2$, $CO_2$), fatty acids, steroid hormones, and fat-soluble vitamins, directly across the lipid bilayer.

Osmosis

The net flow of water across a semipermeable membrane in response to a gradient in the chemical activity of water.

Aquaporins

Membrane water channels through which water molecules passively cross lipid bilayers.

Channel-mediated facilitated diffusion

Passive transport of hydrophilic ions (such as $K^+$, $Na^+$, $Ca^{2+}$, and $Cl^-$) across the plasma membrane through protein channels with open or closed gates.

Carrier-mediated facilitated diffusion

Passive transport of solutes such as glucose, fructose, galactose, and some vitamins using a membrane transporter protein that cannot catalyze net flux against an electrochemical gradient.

Osmotic pressure

The hydrostatic pressure that eliminates the net flux of water from pure water (Side 1) to a solution (Side 2) across a semipermeable membrane.

Hemolysis

The swelling and bursting of a red blood cell when placed in a hypotonic solution due to net osmotic influx of water.

Crenation

The shrinking and spiky alteration of a red blood cell when placed in a hypertonic solution due to net osmotic efflux of water.

Saturability

A diagnostic characteristic of carrier-mediated transport resulting from a finite number of transporters with a finite turnover rate, described by the rate equation $J = \frac{J_{\text{max}}[S]}{K_t + [S]}$.

Selectivity

A diagnostic characteristic of carrier-mediated transport where each transport protein can accept only a limited range of chemical structures as substrates due to its unique 3D structure.