Chapter 7 Membrane Transport

Lecture 19

Passive transport

(no energy required) molecules more down their concentration gradient

3 types of passive transport

Simple diffusion, facilitated diffusion, osmosis

Active transport

(requires energy) Moves molecules against (up) their concentration gradient (low to high)

Permeability of the Lipid Bilayer 

Molecules can cross a phospholipid bilayer (without a transporter) and molecules that can not cross

Molecules that CAN cross a phospholipid bilayer (without a transporter)

Small polar uncharged

Water

Hydrophobic (nonpolar) molecules

Molecules that CANNOT cross a phospholipid bilayer (without a transporter)

Large polar molecules (like sugars, amino acids)

Charged molecules (ions)

Passive transport has 2 diffusions across a membrane

Simple diffusion and facilitated diffusion

Simple diffusion

Tendency for molecules to spread out evenly into the available space

Molecules diffuse down their concentration gradient from high to low concentration

Diffusion requires

no energy

Equilibrium means no net movement

Movement in both in and out at an equal rate

Facilitated diffusion

Molecules move down their concentration gradient from high to low concentration

Transport proteins

Membrane proteins that assist ions and large polar molecules across the membrane

Each transporter is very specific for the molecules it moves 

Types of transport proteins 

Channel protein (tiny particles)

Carrier Proteins (large particles)

Channel proteins 

Provide a corridor (pore) for a molecule or ion to cross the membrane 

Ex; Aquaporins, ion channels 

Aquaporins (2003 nobel prize Peter Agre)

Water channel, a transport protein

Found only in some cells and allows rapid water movement

Ion channels

In neurons, heart, and muscle cells

They move down their electrochemical gradients

Carrier proteins 

Change shape into move substances across the membrane For large polar amino acids and sugars 

Osmosis (Memorize) 

Movement of water across a semipermeable membrane 

Water moves from a region of low osmolarity to higher osmolarity

Calculating osmolarity

Molarity x (number of solute particles) 

Units= Osmolar (OSM)