chapter09

chapter09 - BCH 4053 Summer 2001 Chapter 9 Lecture Notes...

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Chapter 9, page 1 BCH 4053 Summer 2001 Chapter 9 Lecture Notes Slide 1 Chapter 9 Membranes and Cell Surfaces Slide 2 Membranes • Plasma membrane separates “inside” from “outside” of cell • Organelles in eukaryotic cells surrounded by specific membranes • Membranes serve as barriers to contain most substances on one side or the other • Only small, lipid soluble, molecules are permeable to membranes Membranes of organelles are different in composition from that of the plasma membrane. Mitochondria have two membranes, an outer membrane which has some pores that allow passage of medium sized molecules, and an inner membrane which serves as the permeability barrier as well as the energy transducing structure in oxidative phosphorylation. Slide 3 Membranes, con’t. • Membranes have many functions • Allow specific movement of substances into or out of cell, and into or out of organelles • Provide mechanism of energy storage and coupling for both transport and metabolic processes • Involved in cell-cell recognition and interactions • Signal transduction from external stimuli • Locomotion, reproduction Chloroplasts have a membrane separating the oranelle from the rest of the cell, but also contains a set of layered membranes called thylakoid membranes within the chloroplast structure.
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Chapter 9, page 2 Slide 4 Membrane Composition • Membranes are composed of lipids and proteins • Lipids provide the organizational backbone • Proteins provide most of the specific functional features of membranes Slide 5 Lipid Aggregate Structures • The hydrophobic effect is the main factor causing lipids to aggregate • Aggregation can take several forms • Monolayers • Micelles • “Reverse” micelles • Bilayers • (See Figure 9.2) As lipid molecules aggregate, there is a repulsion between neighboring polar head groups, particularly those with a net charge. In fatty acid salts, this repulsion causes the head groups to occupy the maximum area possible, which is a sphere, so the micelles of fatty acid salts are spherical. For phosphoglycerolipids with two hydrocarbon chains, the cross-sectional area of the two chains is large enough that the head group repulsion is minimized, and the aggregates form sheet-like structure instead. Slide 6 Lipid Aggregate Structures, con’t. • Micelles are characterized by a “critical micelle concentration” (CMC) • This is the concentration of monomer in equilibrium with the micelle • The CMC decreases as the hydrophobic part of the molecule gets larger (i.e. as MW increases) • Detergents that form such micelles are used to disrupt membrane and protein structures • See Figure 9.3
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Chapter 9, page 3 Slide 7 Lipid Aggregate Structures, con’t. • Bilayer structures wrap to form “vesicles”, which
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chapter09 - BCH 4053 Summer 2001 Chapter 9 Lecture Notes...

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