Lecture 30-33 - Biological membranes

Lecture 30-33 - Biological membranes - Biological Membranes...

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Biological Membranes Consist of same chemical components (proteins and lipids) in prokaryotes and eukaryotes. Trilaminar appearance. Asymmetrical: inner dense layer THICKER than outer dense layer. Chemical asymmetry: orientation of proteins gives membranes “sidedness.” Dynamic structures. WHY? Allows cells to change shape and position. “Organized sea” of fluid lipid, proteins and lipids are able to move/interact. Membranes control the composition of space they bound by excluding some molecules and selectively transporting others. 5-8 nm thick
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Biological membranes act not only as semi-permeable barriers, but also act in cellular signaling. Protein receptors : bind hormones, and growth/metabolic regulators. Lipids and proteins! Membrane receptors transmit information through a series of intracellular chemical intermediates called “second messengers.” http://www.sidwell.edu/us/science/21bio/new/thigmo_signal.htm
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The lipid and protein contents of membranes will vary from membrane to membrane. Overall, lipids are the major components of eukaryotic membranes.
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Three major lipid components of eukaryotic membranes: 1. Glycerophospholipids 2. Sphingolipids (i.e. sphingomyelin) 3. Cholesterol If contain a phosphate, they are called phospholipids. Glycerol backbone Glycerophospholipidsmost abundant lipid of membranes. Phosphate esterified to α carbon. Asymmetric molecule. Two long chain fatty acids esterified to other carbons.
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1,2-Diacylglycerol 3-phosphate Parent compound of several glycerophospholipids. Amphipathic: polar headgroup (charged phosphate) and nonpolar tail (hydrophobic hydrocarbon chains). Both polar and hydrophobic!
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Phosphatidylcholine and phosphatidylethanolamine are the most common glycerophospholipids in membranes:
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Phosphatidylglycerol phosphoglyceride (diphosphatidylglycerol or cardiolipin) contains two phosphatidic acids linked by a glycerol and is found nearly exclusively in mitochondrial inner membranes . Phosphatidylinositol is present in plasma membranes. It is the source of inositol trisphosphate and diacylglycerol, referred to as “second messengers,” that are involved in the action of some hormones.
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Glycerophospholipids contain two fatty acyl groups esterified to carbon atoms 1 and 2 of glycerol; some of the major fatty acids found in glycerophospholipids are presented in Table 12.1. A saturated fatty acid is usually found on C-1 of the glycerol and an unsaturated fatty acid on C-2. Designation of the different classes of glycerophospholipids does not specify which fatty acids they contain. Common Name Systematic Name Structural Formula Myristic acid n -Tetradecanoic CH3 (CH2)12 COOH Palmitic acid n -Hexadecanoic CH3 (CH2)14 COOH Palmitoleic acid cis- 9-Hexadecenoic CH3 (CH2)5 CHCH (CH2)7 COOH Stearic acid n -Octadecanoic CH3 (CH2)16 COOH Oleic acid cis -9-Octadecenoic acid CH3 (CH2)7 CHCH (CH2)7 COOH Linoleic acid cis,cis -9,12-Octadecadienoic CH3 (CH2)3 (CH2CHCH)2 (CH2)7 COOH Linolenic acid cis,cis,cis
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Lecture 30-33 - Biological membranes - Biological Membranes...

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