Cell Membrane Lecture Part 1

Cell Membrane Lecture Part 1 - Membrane Structure and...

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Membrane Structure and Function (Chapter 7)
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Overview: Life at the Edge The plasma membrane is the barrier that encloses cellular organelles. Function: Separates cell from surroundings Controls traffic into and out of cell The plasma membrane is selectively permeable Allows some substances to cross more easily than others
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Membrane Composition Composed of mainly phospholipids and proteins Phospholipids are the most abundant lipids in the plasma membrane 2 Fatty Acids, glycerol, phosphate group Phospholipids are amphiphatic molecules . Contains hydrophilic and hydrophobic regions Phospholipids spontaneously form a bilayer in water. Why?
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Figure 7.2 Hydrophilic head Hydrophobic tail WATER WATER
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Membranes are fluid mosaics of lipids and proteins Arrangement of lipids and proteins in a membrane are explained by the fluid mosaic model. Mosaic of proteins embedded in or attached to phospholipid bilayer
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Figure 7.3 Phospholipid bilayer Hydrophobic regions of protein Hydrophilic regions of protein Fluid Mosaic Model
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Previous Models 1915- Membranes isolated and analyzed Contained lipids and proteins 1925 Scientists reasoned that cell membranes must be phospholipid bilayers Bilayers arranged so hydrophobic tails are sheltered from water while hydrophilic heads interact with water 1935- Davson Danielii sandwich model Bilayer lies between two layers of globular protein
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Sandwich Model Problems
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Problems with D-D Model Not all membranes are alike Different chemical composition and structures Proteins are not soluble in water Like lipids, proteins are also amphiphatic molecules If proteins were at the membrane surface, then their hydrophobic molecules would be in contact with water Not likely
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FFM’s Inception 1972- Singer and Nicholson proposed that membrane proteins reside in the bilayer In this model, hydrophilic regions are exposed to water while hydrophobic regions are sheltered in the non- aqueous region Membrane is a mosaic of proteins bobbing in a fluid bilayer of phospholipids Freeze Fracture Method
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Cell Membrane Lecture Part 1 - Membrane Structure and...

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