NPB 110A W26: L06 Biomembrane Transport

What is diffusion?

movement of molecules from one location to another as a result of their random thermal motion

Initially, ________ concentration of molecules randomly move toward ________ concentration, Over time, ________ molecules placed in a ________ will evenly distribute themselves.

higher; lower; solute; solvent

Net flux accounts for solute movements in ________ directions.

both

What is diffusion limited by?

distance → moves very slow

The cell membrane is selectively ________

permeable

What are cell membranes permeable to (3)?

small hydrophic molecules, small uncharged molecules, gases

What are cell membranes slightly permeable to (2)?

water and urea

What are cell membranes impermeable to (2)?

ions and large uncharged polar molecules

Non-permeable molecules enter the cell with the assistance of ________ proteins.

transmembrane

What are 3-4 general types of transmembrane proteins?

channels, transporters/carriers (uniporters, cotransporters—symporters, antiporters), pumps

What are channels?

transmembrane proteins that passively transport of ions, water, and small molecules across the cell membrane via facilitated transport/facilitated diffusion by forming a pore.

What are transporters/carriers?

transmembrane proteins that facilitate the movement of a wide variety of ions & molecules through the cell membrane

How many/what types of transporters/carriers are there?

3 types: uniporters (passive); cotransporters (secondary active, 2 reactions) —symporters, antiporters

What are uniporters?

a transporter/carrier transmembrane proteins that facilitate the passive transport of a single type of molecule down its concentration gradient (from high to low) using facilitated diffusion

What are cotransporters?

a transporter/carrier transmembrane protein that transport 2 or more types of molecules simultaneously, using ion gradients created by other transporters; includes symporters & antiporters, using secondary active transport

What are symporters?

a type of cotransporter that moves 2 or more types of molecules in the same direction across a membrane, using secondary active transport

What are antiporters?

a type of cotransporter that moves 2 or more types of molecules in opposite directions across a membrane, using secondary active transport.

What are pumps?

transmembrane proteins that actively transport ions and molecules against their concentration; coupled to hydrolysis of ATP (primary active transport)