BSC 300 2023_TM Lecture #8_Membrane Transport_In Class Lecture Slides

Spontaneous movement of material from a region of high concentration to a region of low concentration Diffusion is energetically favorable (exergonic transport).

Active transport moves materials from low to high concentration and requires external energy; passive transport moves materials from high to low concentration without energy Active transport is energetically unfavorable (endergonic transport).

The spontaneous diffusion of water through a semipermeable membrane Water moves from areas of lower solute concentration to areas of higher solute concentration.

• Simple diffusion • Facilitated diffusion • Active transport • Osmosis

Protein-mediated transport that is faster than simple diffusion and highly specific The transport rate is limited by the number of transporters (Vmax) and transporter affinity (Km).

Specialized protein channels that allow passive movement of water They increase the rate of water transport across membranes.

It binds glucose in an outward-open conformation, transitions through occluded states, and releases glucose in an inward-open conformation The process depends on Km and glucose concentration.

Transmembrane proteins that couple energy from ATP hydrolysis to transport substances against concentration gradients Examples include the sodium-potassium pump.

Transport a wide array of substrates, including toxins and drugs, into or out of the cell They are primarily exporters but can import molecules.

Transports Na+ out and K+ into the cell at a ratio of 3 Na+ to 2 K+ It is a classic example of a P-type ATPase.

Na+ channels open, causing membrane depolarization, followed by K+ flow for repolarization Na+ channels become inactivated after an AP, leading to a refractory period.

• Voltage-gated channels • Ligand-gated channels • Mechano-gated channels

The coupling of active transport to existing ion gradients to transport another molecule or ion against its concentration gradient It can be symport (same direction) or antiport (opposite directions).

The use of energy stored in an ionic gradient to transport other molecules An example is the sodium/glucose symporter.

Transport of substances across polarized epithelial cells involving different transport proteins on apical and basolateral surfaces Examples include the transport of glucose from the intestinal lumen to the blood.

The membrane potential of a nerve or muscle cell, maintained by K+ gradients It is subject to change when the cell is activated.

They generate an electric potential across the membrane without significantly changing intraluminal pH H+ accumulation can lower luminal pH.