Lipids and Membranes Flashcards Preview

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Flashcards in Lipids and Membranes Deck (32):
1

Amphiphilic

Containing both polar and nonpolar regions

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4 major classes of lipids

Fatty acids
Phospholipids
Glycosphingolipids
Isoprenoids

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Simplest class of lipids

Fatty acids

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Fatty acid nomenclature

Carboxyl group is C-1
Main chain is named as usual
Unsaturations: delta^n (n= carbon where double bond is located)

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Effects of unsaturations in fatty acid chains

Increased flexibility: looser packing
Lowered melting point

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Triacylglycerols

3 fatty acids esterified with one molecule of glycerol
Hydrophobic storage form of fatty acids
Most abundant lipid form

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Metabolism of triacylglycerols

Broken down in small intestine by lipases

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Glycerophospholipids

Compose majority of membranes
Amphiphilic molecules (polar head, nonpolar tail)

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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)

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Phospholipases

Class of enzymes that catalyze cleavage of esters in phospholipids

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Plasmalogens

Form of glycerophospholipid with C-1 substituent linked by vinyl ether linkage
Found in CNS as well as peripheral nerve and muscle tissue

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Sphingolipids

Sphingosine backbone
Particularly abundant in CNS cells

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Ceramide

Precursor of all other sphingolipids

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Sphingomyelins

Class of sphingolipid
Phosphocholine at C-1
Major component of myelin sheath

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Cerebrosides

Class of sphingolipid
Monosaccharide attached through beta-glycosidic bond
Abundant in nerve tissue and myelin sheaths
Different subclasses, depending on ID of sugar

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Gangliosides

Class of sphingolipid
Linked to complex oligosaccharide containing N-acetylneuraminic acid
Used in cell-surface signaling

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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

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Waxes

Nonpolar esters of long-chain fatty acids and long-chain monohydroxylic alcohols

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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

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Formation of lipid bilayers

Spontaneous formation: hydrophobic interactions

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Lipid-to-protein ratio of biological membranes

25-50% lipid
50-75% protein
<10% carbohydrate

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Fluid-mosaic model

Membranes are dynamic structures in which lipids and proteins can rapidly rotate and diffuse

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Flippase and floppase

Enzymes which catalyze transverse diffusion of certain phospholipids

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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)

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Liposomes

Synthetic vesicles composed of lipid bilayers that enclose an aqueous compartment
Great method for solubilizing certain drugs and delivering them within the body

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Integral membrane proteins

Span the bilayer completely (hydrophobic middle)
Includes pores and channels used in passive and active transport

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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

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Lipid-anchored membrane proteins

Tethered to membrane through covalent bond to lipid anchor

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Membrane transport depends on...

Concentration gradient
Charge gradient

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Passive transport

Movement of solute down its concentration gradient without expenditure of energy
Continues until concentration gradient is equalized

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Active transport

Requires energy to move molecule up its concentration gradient
Usually uses ATP as energy source

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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