Transcript Transport by Carriers

TRANSPORT ACROSS CELL
MEMBRANES
Transport by Carriers
Learning Outcomes
B9 - Describe the structure and function of
the cell membrane:
 Describe and compare: facilitated transport and
active transport in terms of:
Method of transport (use of channel or carrier protein)
 Use of energy (active vs. passive)
 Concentration gradient
 Type / size of molecule transported

Review of Membrane Structure
 What substances can diffuse through the plasma
membrane? What substances cannot?
 What moves in and out of cells by osmosis? What
controls this process?
 What are two types of membrane proteins that
assist with transport of substances across the
membrane?
Transport by carriers
 Carrier proteins are found within the cell membrane
 Specific for certain molecules or ions which cannot
pass through the membrane by diffusion
 2 types:


Passive - with the concentration gradient (high to low) -no
energy required
Active - against the concentration gradient (low to high) –
energy (ATP) required
Facilitated Transport
Facilitated Transport
 Uses a protein carrier
 With the concentration gradient
 Does not require energy
 Moves molecules that are too large to cross the
membrane on their own
 Examples: glucose, amino acids
 Also known as facilitated diffusion (why?)
Active Transport
Active Transport
 Uses a protein carrier
 Against the concentration gradient (low to high)
 Requires energy (ATP)
 Used to build up a concentration of a substance on
one side of the membrane (why might this be
necessary?)
Examples of active transport:
 To concentrate iodine in thyroid cells
 Sodium-potassium pump in nerve, muscle and other
cells
 Movement of salt in or out of cells to drive osmosis
(ex. kidneys)
 Movement of ions to control pH
Sodium Potassium Pump.flv
Sodium Potassium Pump.flv
Proton pump
Comparing methods of transport
Gap Junctions
 Some protein
channels connect
adjacent cells
 Allow passage of
materials from one
cell to another
 Can be active or
passive