Plasma Membrane Structure and Function
Plasma Membrane Structure and Function
• separates the cytoplasm from the environment
• it controls the traffic of molecules into and out of cells (selectively permeable)
• it is the surface of the cell which is recognized by other
cells, by hormones, or by antibodies
Membrane Lipids
1. Phospholipids
- most abundant lipids in the membrane. They:
i) spontaneously form layers on the surface of water
ii) are amphipathic molecules (hydrophobic/hydrophilic)
iii) move around in the membrane
iv) have varying degrees of unsaturation in their tails
(determines fluidity at lower temperatures)
2. Glycolipids
- glycolipids are like a phospholipid, but with sugars attached at the head region.
They are found only on the outside layer of the plasma membrane. Their function is to:
i) protect the cell surface
ii) act as recognition sites
iii) help cells stick to surfaces
3. Cholesterol
- small, flat ringed structure (steroid) that occurs between phospholipid molecules in the membrane. Their function is to:
i) make membranes less fluid
ii) make membranes less permeable
iii) make membranes tougher
Membrane Proteins
Membrane proteins have a variety of functions:
• ENZYMES
• TRANSPORT
• RECEPTORS
• FORMATION OF JUNCTIONS
• CELL-CELL RECOGNITION
• ATTACHMENT TO EXTRACELLULAR MATRIX
Membrane proteins have the following properties:
• hydrophobic and hydrophilic regions
• proteins moved around in the membrane
• some proteins actually protruded on both sides of the
membrane!!
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