Module 3 - 3a1: Intro to Membranes • Plasma membranes...

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Unformatted text preview: 3a1: Intro to Membranes • Plasma membranes enclose entire cell • Examples of internal membranes: lyosomal membrane, endoplasmic reticulum, nuclear envelope, chloroplast membrane, mitochrondrial membrane • Dynamic structures capable of fusing without losing continuity o Ex. vesicles fusing with plasma membrane, plasma membranes of two different cells • Functions: o Eukaryotic: compartmentalization, provides selectively permeable membrane (some solutes preferentially enter over others), transport solutes, responds to external signals (signal transduction), intracellular interaction 3a2: Overview of Plasma Membrane Structure • Polar lipids, proteins, carbohydrates • Appearance in electron microscope: thin sectioning technique (dark, light, dark appearance), heavy metals deposit where this is a dark stain, 7.5nm • Freeze fracture technique: two fracture faces • Fluid mosaic model (1972): lipid bilayer is core of membrane, proteins occur as mosaic of discontinuous molecules, components are mobile, some proteins penetrate deeply or through • Polar lipids o Organized as bilayer, polar head groups interact with water, non polar tails interaction stabilized as hydrophobic molecules 3a3: Membrane Lipids • All are amphipatic • All contain phosphate group except glycolipids and cholesterol • Phospholipids, have glycerol backbone: phosphoglycerides • Phosphoglycerides: 3 rd OH group has phosphate o Choline o Ethanlomine o Serine o Inositol • Diglycerides: often one saturated and one unsaturated • Sphingolipids: sphingosine-based lipids, amino alcohol with long hydrocarbon chain o Two additions: Always a fatty acid to amino group of sphingosine • This a ceramide o Additional groups esterified to OH to terminal OH If carbohydrate, molecule is glycolipid If phosphorylcholine, molecule is sphingomyelin 3a4: Plasma Membrane Carbohydrates • Covalently linked to either protein or lipid • All of carbohydrate faces outward into extracellular space o Glycocalyx • Glycorproteins o Carbohydrate present in short branched oligosacchardies (<15 sugar per chain) o May be attached to R group of Asparagines (ends in NH2): N-linked Serine and threonine (ends in OH): O-linked o Play roles in cell interactions • Glycolipids o May play role in certain infectious diseases o Carbohydrates of glycolipids determine blood type 3a5: Membrane Proteins • 20-50 different ones, asymmetrically situated • Properties of outer portion of membrane very diff from properties of inner • 3 distinct classes based on relationship to lipid bilayer • Integral proteins o Penetrate into lipid bilayer o Usually pass right through Have segments protruding into extra cellular space, into cytoplasm o Transmembrane segments Pass through lipid bilayer Usually consist of nonpolar amino acids organized in alpha-helix Some can form aqueous channel through lipid bilayer • Peripheral membrane proteins o Located entirely outside lipid bilayer, either on extracellular or cytoplasmic surface...
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This note was uploaded on 06/12/2011 for the course BIOL 130 taught by Professor Bols during the Fall '08 term at Waterloo.

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Module 3 - 3a1: Intro to Membranes • Plasma membranes...

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