Download NOTES 2 Membrane_Transport - MacWilliams Biology

II. Movement across
the Cell Membrane
A. Simple Diffusion
1. Movement for high concentration [ ] to
low concentration [ ]
a. “passive transport”
b. no energy needed
Diffusion Animation
2.
Diffusion across cell membrane
a. Cell membrane is the boundary
between inside & outside…

separates cell from its environment
OUT
IN
food
carbohydrates
sugars, proteins
amino acids
lipids
salts, O2, H2O
OUT
IN
waste
ammonia
salts
CO2
H2O
products
cell needs materials in & products or waste out
3. Diffusion through phospholipid bilayer
a. What molecules can get through
directly?

fats & other lipids
inside cell
NH3
lipid
salt
b. What molecules can
NOT get through
directly?
i. polar molecules
 H 2O
ii. ions
outside cell
sugar aa
H 2O
 salts, ammonia
iii. large molecules
 starches, proteins
4. Channels through cell membrane
a. Membrane becomes semi-permeable with
protein channels
. specific channels allow specific material
across cell membrane
 Called TRANSPORT or CARRIER PROTEINS
inside cell
NH3
salt
H 2O
aa
sugar
outside cell
B. Facilitated Diffusion Facilitated Diffusion Animation
1. Diffusion through protein channels
a. channels move specific molecules across
cell membrane
facilitated = with help
b. NO energy needed
open channel = fast transport
high
low
“The Bouncer”
C. Active Transport
1. Cells may need to move molecules against
concentration gradient
a. shape change transports solute from
one side of membrane to other
b. protein “pump”
c. “costs” energy = ATP low conformational change
ATP
high
“The Doorman”
Active Transport Example: Nerve Impulse
1.
Neurons, nerve cells, have a charge, or electrical potential,
across their cell membranes.
2. Sodium (Na+) is on the outside of the cell and Potassium (K+) is
on the inside
3. The neuron is at rest when the inside of the cell is at -70mV
4. An “action potential” occurs when the nerve is stimulated and
sodium moves INTO the cell. The positive Na+ moving into the
cell turns the inside positive. Facilitated diffusion
5. After the Na+ channels open, K+ channels open and K+ moves
OUT of the cell to reset the negative charge inside the cell.
Facilitated diffusion
The Nerve Impulse
6. Eventually Na+ must move back OUT of the cell and K+ must
move back IN against their concentration gradients. This occurs
by Active transport. A Na+/K+ pump is used to move these ions
back to their original sides of the cell membrane.
Neuron: Na+/K+ Pump
Na+/K+ pump
D. Review of Membrane Transport
1. Passive Transport

Simple diffusion
 diffusion of nonpolar, hydrophobic molecules
 lipids
 High to low concentration gradient

Facilitated transport
 diffusion of polar, hydrophilic molecules
 through a protein channel
 High to low concentration gradient
2. Active transport

diffusion against concentration gradient
 Low to high


uses a protein pump
requires ATP
ATP
Transport summary
simple
diffusion
facilitated
diffusion
active
transport
ATP
E. Moving large molecules in & out of cell
Large molecules are IMPERMEABLE to
the cell membrane (can’t get through)
 There is a way… through vesicles &
vacuoles
1. Endocytosis (moving in to cell)

 phagocytosis = “cellular eating”
Phagocytosis Animation
 pinocytosis = “cellular drinking”
Exocytosis (moving out of cell)
Endo and Exocytosis Animation
2.
Endocytosis
phagocytosis
pinocytosis
fuse with
lysosome for
digestion
non-specific
process
EXOCYTOSIS
Cellular Transport
Interactive animation
http://www.wiley.com/college/boyer/0470003790/animations/
membrane_transport/membrane_transport.htm