http://www.expertsmind.com/topic/biology/microbiology-92241.aspx

1. Membrane Biology

2. Plasma Membrane Structure and Function
• The plasma membrane separates the internal
environment of the cell from its surroundings.
• The plasma membrane is a phospholipid
bilayer with embedded proteins.
• The plasma membrane has a fluid consistency
and a mosaic pattern of embedded proteins.

3. Fluid-mosaic model of membrane structure

4. • Cells live in fluid environments, with
water inside and outside the cell.
• Hydrophilic (water-loving) polar heads of
the phospholipid molecules lie on the
outward-facing surfaces of the plasma
membrane.
• Hydrophobic (water-fearing) nonpolar
tails extend to the interior of the plasma
membrane.

5. • Plasma membrane proteins may be
peripheral proteins or integral proteins.
• Aside from phospholipid, cholesterol is
another lipid in animal plasma
membranes; related steroids are found in
plants.
• Cholesterol strengthens the plasma
membrane.

6. Functions of membrane proteins
• Membrane proteins have a variety of
functions.
• Some help to transport materials across the
membrane.
• Others receive specific molecules, such as
hormones.
• Still other membrane proteins function as
enzymes.

7. Channel protein

8. Carrier protein

9. Cell recognition protein

10. Receptor protein

11. The Permeability of the Plasma Membrane
• The plasma membrane is differentially
permeable.
• Macromolecules cannot pass through because
of size, and tiny charged molecules do not
pass through the nonpolar interior of the
membrane.
• Small, uncharged molecules pass through the
membrane, following their concentration
gradient.

12. How molecules cross the plasma
membrane

13. • Movement of materials across a membrane
may be passive or active.
• Passive transport does not use chemical
energy; diffusion and facilitated transport are
both passive.
• Active transport requires chemical energy and
usually a carrier protein.
• Exocytosis and endocytosis transport
macromolecules across plasma membranes
using vesicle formation, which requires
energy.

14. Diffusion and Osmosis
• Diffusion is the passive movement of
molecules from a higher to a lower
concentration until equilibrium is
reached.
• Gases move through plasma membranes
by diffusion.

15. Process of diffusion