Lipids and Membranes Flashcards
Amphiphilic
Containing both polar and nonpolar regions
4 major classes of lipids
Fatty acids
Phospholipids
Glycosphingolipids
Isoprenoids
Simplest class of lipids
Fatty acids
Fatty acid nomenclature
Carboxyl group is C-1
Main chain is named as usual
Unsaturations: delta^n (n= carbon where double bond is located)
Effects of unsaturations in fatty acid chains
Increased flexibility: looser packing
Lowered melting point
Triacylglycerols
3 fatty acids esterified with one molecule of glycerol
Hydrophobic storage form of fatty acids
Most abundant lipid form
Metabolism of triacylglycerols
Broken down in small intestine by lipases
Glycerophospholipids
Compose majority of membranes Amphiphilic molecules (polar head, nonpolar tail)
Phosphatidates
Form of glycerophospholipids
Have glycerol backbone, fatty acids at C-1 and C-2 and phosphate at C-3
Present in small amounts (rather rare)
Phospholipases
Class of enzymes that catalyze cleavage of esters in phospholipids
Plasmalogens
Form of glycerophospholipid with C-1 substituent linked by vinyl ether linkage
Found in CNS as well as peripheral nerve and muscle tissue
Sphingolipids
Sphingosine backbone
Particularly abundant in CNS cells
Ceramide
Precursor of all other sphingolipids
Sphingomyelins
Class of sphingolipid
Phosphocholine at C-1
Major component of myelin sheath
Cerebrosides
Class of sphingolipid
Monosaccharide attached through beta-glycosidic bond
Abundant in nerve tissue and myelin sheaths
Different subclasses, depending on ID of sugar
Gangliosides
Class of sphingolipid
Linked to complex oligosaccharide containing N-acetylneuraminic acid
Used in cell-surface signaling
Steroids
Classified as isoprenoids Shared fused, four-ring structure Derived from squalene Hydrophobic Precursor of steroid hormones and bile salts as well as component of certain membranes
Waxes
Nonpolar esters of long-chain fatty acids and long-chain monohydroxylic alcohols
Functions of biological membranes
Separation of cellular components
Generation and maintenance of ion and small molecule gradients
Assistance of biosynthesis and delivery of transmembrane proteins
Formation of lipid bilayers
Spontaneous formation: hydrophobic interactions
Lipid-to-protein ratio of biological membranes
25-50% lipid
50-75% protein
<10% carbohydrate
Fluid-mosaic model
Membranes are dynamic structures in which lipids and proteins can rapidly rotate and diffuse
Flippase and floppase
Enzymes which catalyze transverse diffusion of certain phospholipids
Factors affecting membrane fluidity
Increased temp- increased fluidity
Unsaturated fatty acids- increased fluidity
Cholesterol: decreased fluidity at high temps, increased fluidity at low temps (fluidity buffer)
Liposomes
Synthetic vesicles composed of lipid bilayers that enclose an aqueous compartment
Great method for solubilizing certain drugs and delivering them within the body
Integral membrane proteins
Span the bilayer completely (hydrophobic middle)
Includes pores and channels used in passive and active transport
Peripheral membrane proteins
Associated with one face of membrane through charge-charge interactions and/or H-bonding with integral membrane proteins or polar head groups
Lipid-anchored membrane proteins
Tethered to membrane through covalent bond to lipid anchor
Membrane transport depends on…
Concentration gradient
Charge gradient
Passive transport
Movement of solute down its concentration gradient without expenditure of energy
Continues until concentration gradient is equalized
Active transport
Requires energy to move molecule up its concentration gradient
Usually uses ATP as energy source
2 types of active transport
Primary active transport: powered by direct source of energy
Secondary active transport: uses ion concentration gradient to power second transport process
