chapter 5 (Membrane structure) 
Membrane proteins
Ways to move across membranes
Factors that affect membrane
fluidity
Movements of phospholipids
Integral
peripheral
Transmembrane proteins:
The integral protein is physically embedded
in the hydrophobic portion of the membrane.
Lipid anchored proteins An amino acid of the integral protein is
covalently attached to a lipid
Non-covalently bound to an integral protein.
or to the polar head of a phospholipid
Rotational
Lateral
Flip-flop
Phospholipids flip from one leaflet to the
opposite leaflet.
This movement requires ATP and Flippase
enzyme.
Phospholipids rotate around their long axes.
Phospholipids move laterally within the
membrane
Phospholipids move laterally within the
membrane.
*demonstrated by the Larry and Michael
experiment using mouse and human cells
Presence of doubl bound
Presence of cholesterol
Length of fatty acid tails
The shorter the fatty acid tails, the more fluid
the membrane
In the fatty acid tails increases fluidity of the
membrane.
At high temperatures: cholesterol decreases
fluidity of the membrane.
• At low temperatures: cholesterol increases
fluidity of the membrane
Passive transport
Active transport
Solutes move with gradient (from higher to
lower concentration). Requires no energy
.
1-Passive diffusion
Without help of transport proteins
.
2-Facilitated diffusion
With help of transport proteins.
Solutes move against gradient (from lower to
higher concentration).
Requires energy.
Transport proteins
Channels
Transporters
open passageway for direct diffusion of ions.
Most channels are gated.
Example: Aquaporins (water channel)
**Uniporter
Transports a single molecule.
Symporter \ cotransporter
Transports two or more molecules in the
same direction
Antiporter
Transports two or more molecules in
opposite directions**
Transport of large molecules
Exocytosis
Endocytosis
Materials inside the cell packaged into
vesicles and secreted outside the cell
plasma membrane folds inward to form a
vesicle that brings substances inside the cell
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Receptor-mediated endocytosis
Pinocytosis
Phagocytosis