MEMBRANE STRUCTURE &
FUNCTIONS
MEMBRANE STRUCTURE AND FUNCTION
Recall: Membranes are made of phospholipids, which have
a phosphate group attached to fatt...
MEMBRANE STRUCTURE AND FUNCTION
The amphipathic nature of phospholipids means that it
forms a bilayer or a single-layer mi...
MEMBRANE STRUCTURE AND FUNCTION
A bilayer arrangement allows the membrane to have
water on either side.
Water
Water
Hence ...
MEMBRANE STRUCTURE AND FUNCTION
This bilayer is not static; it is dynamic. There is fluidity in
the membrane.
MEMBRANE STRUCTURE AND FUNCTION
Fluidity is assisted by sterols (i.e. Cholesterol in animal cells)
Sterols stabilize the m...
MEMBRANE STRUCTURE AND FUNCTION
At high temperatures, sterols restrain movement of
phospholipids
At low temperatures, ster...
MEMBRANE STRUCTURE AND FUNCTION
Fluid mosaic model: Membranes are fluid (not rigid);
proteins embedded in the lipids float...
MEMBRANE STRUCTURE AND FUNCTION
Two types of membrane proteins:
1) Integral membrane protein – protein embedded in the
lip...
MEMBRANE STRUCTURE AND FUNCTION
Two types of membrane proteins:
MEMBRANE STRUCTURE AND FUNCTION
Some integral proteins are transmembrane proteins
because they cross the thickness of the ...
MEMBRANE STRUCTURE AND FUNCTION
How are proteins embedded in the membrane?
The amino acids of the
protein that cross the c...
MEMBRANE STRUCTURE AND FUNCTION
How are proteins embedded in the membrane?
These nonpolar (hydrophobic) amino acids are of...
MEMBRANE STRUCTURE AND FUNCTION
How are proteins embedded in the membrane?
hydrophobic
hydrophilic
hydrophilic
MEMBRANE STRUCTURE AND FUNCTION
How are proteins embedded in the membrane?
Hydrophobic section with
nonpolar R-groups
MEMBRANE STRUCTURE AND FUNCTION
Functions of membrane proteins:
1) Transport
2) Receptor
3) Enzyme
4) Anchor (attachment)/...
MEMBRANE STRUCTURE AND FUNCTION
Functions of membrane proteins:
1) Transport proteins: Move molecules and ions across a
me...
MEMBRANE STRUCTURE AND FUNCTION
Functions of membrane proteins:
1) Transport proteins: can be channel and carrier proteins...
MEMBRANE STRUCTURE AND FUNCTION
Functions of membrane proteins:
1) Transport proteins: Some can transport two substances i...
MEMBRANE STRUCTURE AND FUNCTION
Functions of membrane proteins:
2) Receptor proteins: relays signals between cells interna...
MEMBRANE STRUCTURE AND FUNCTION
Functions of membrane proteins:
3) Enzyme proteins: catalyzes reactions at the membrane
MEMBRANE STRUCTURE AND FUNCTION
Functions of membrane proteins:
4) Anchor (attachment)/recognition proteins: Attachment
po...
MEMBRANE STRUCTURE AND FUNCTION
Functions of membrane proteins:
4) Anchor (attachment)/recognition proteins: Immune cells
...
MEMBRANE STRUCTURE AND FUNCTION
Functions of membrane proteins:
4) Anchor (attachment)/recognition proteins: Often have
ca...
MEMBRANE STRUCTURE AND FUNCTION
Carbohydrates are often used as “markers” in recognition:
Glycoproteins: Protein with a ca...
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Transcript of "Tang 05 membrane structure and functions"

  1. 1. MEMBRANE STRUCTURE & FUNCTIONS
  2. 2. MEMBRANE STRUCTURE AND FUNCTION Recall: Membranes are made of phospholipids, which have a phosphate group attached to fatty acid (lipid) chains. Phospholipids have a polar and non-polar end, making them amphipathic
  3. 3. MEMBRANE STRUCTURE AND FUNCTION The amphipathic nature of phospholipids means that it forms a bilayer or a single-layer micelle spontaneously in water. Vesicle (bilayer) Micelle (unilayer) Phospholipid bilayer
  4. 4. MEMBRANE STRUCTURE AND FUNCTION A bilayer arrangement allows the membrane to have water on either side. Water Water Hence the cell membrane is called the phospholipid bilayer.
  5. 5. MEMBRANE STRUCTURE AND FUNCTION This bilayer is not static; it is dynamic. There is fluidity in the membrane.
  6. 6. MEMBRANE STRUCTURE AND FUNCTION Fluidity is assisted by sterols (i.e. Cholesterol in animal cells) Sterols stabilize the membrane. Hydrophilic end Hydrophobic end Hydrophobic tail
  7. 7. MEMBRANE STRUCTURE AND FUNCTION At high temperatures, sterols restrain movement of phospholipids At low temperatures, sterols occupy spaces between phospholipids to prevent the lipids from sticking together (enhances fluidity)
  8. 8. MEMBRANE STRUCTURE AND FUNCTION Fluid mosaic model: Membranes are fluid (not rigid); proteins embedded in the lipids float freely.
  9. 9. MEMBRANE STRUCTURE AND FUNCTION Two types of membrane proteins: 1) Integral membrane protein – protein embedded in the lipid bilayer 2) Peripheral membrane protein – protein on the surface of the membrane
  10. 10. MEMBRANE STRUCTURE AND FUNCTION Two types of membrane proteins:
  11. 11. MEMBRANE STRUCTURE AND FUNCTION Some integral proteins are transmembrane proteins because they cross the thickness of the lipid bilayer. Protein crosses the membrane
  12. 12. MEMBRANE STRUCTURE AND FUNCTION How are proteins embedded in the membrane? The amino acids of the protein that cross the cell membrane have hydrophobic R-groups. The parts that are exposed to the environment have hydrophilic R-groups. Gly Ala Val Leu Ile Phe Trp Pro Ala Leu Ile Phe Trp Pro Gly Ala Leu Ile Phe Trp Pro
  13. 13. MEMBRANE STRUCTURE AND FUNCTION How are proteins embedded in the membrane? These nonpolar (hydrophobic) amino acids are often found in the transmembrane sections of proteins.
  14. 14. MEMBRANE STRUCTURE AND FUNCTION How are proteins embedded in the membrane? hydrophobic hydrophilic hydrophilic
  15. 15. MEMBRANE STRUCTURE AND FUNCTION How are proteins embedded in the membrane? Hydrophobic section with nonpolar R-groups
  16. 16. MEMBRANE STRUCTURE AND FUNCTION Functions of membrane proteins: 1) Transport 2) Receptor 3) Enzyme 4) Anchor (attachment)/recognition Some membrane proteins have multiple functions
  17. 17. MEMBRANE STRUCTURE AND FUNCTION Functions of membrane proteins: 1) Transport proteins: Move molecules and ions across a membrane
  18. 18. MEMBRANE STRUCTURE AND FUNCTION Functions of membrane proteins: 1) Transport proteins: can be channel and carrier proteins Channel protein Carrier protein
  19. 19. MEMBRANE STRUCTURE AND FUNCTION Functions of membrane proteins: 1) Transport proteins: Some can transport two substances in opposite directions simultaneously (i.e. sodium potassium pump)
  20. 20. MEMBRANE STRUCTURE AND FUNCTION Functions of membrane proteins: 2) Receptor proteins: relays signals between cells internal and external environments
  21. 21. MEMBRANE STRUCTURE AND FUNCTION Functions of membrane proteins: 3) Enzyme proteins: catalyzes reactions at the membrane
  22. 22. MEMBRANE STRUCTURE AND FUNCTION Functions of membrane proteins: 4) Anchor (attachment)/recognition proteins: Attachment points for cytoskeleton and ECM components; also for cell- cell recognition (i.e. by immune system)
  23. 23. MEMBRANE STRUCTURE AND FUNCTION Functions of membrane proteins: 4) Anchor (attachment)/recognition proteins: Immune cells can identify which cells are foreign, and which cells are infected
  24. 24. MEMBRANE STRUCTURE AND FUNCTION Functions of membrane proteins: 4) Anchor (attachment)/recognition proteins: Often have carbohydrate groups on the extracellular side; these are called glycoproteins
  25. 25. MEMBRANE STRUCTURE AND FUNCTION Carbohydrates are often used as “markers” in recognition: Glycoproteins: Protein with a carbohydrate attached Glycolipid: Lipid with a carbohydrate attached

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