Lipids Highly diverse structures Unifying property Hydrophobic: little to no affinity to water Contains hydrocarbons, which form nonpolar covalent bonds Do not form polymers Biologically important lipids containing molecules: Fats Phospholipids Steroids

Fats Structure - Fatty acid Composed of two different molecules bonded by ester linkage fatty acid & glycerol - Fatty acid Hydrocarbon chain with a carboxyl group at one end Glycerol Three-carbon alcohol Each carbon attached to hydroxyl group Try to Draw

Dehydration reaction in the synthesis of a fat LE 5-11a Fatty acid (palmitic acid) Glycerol Dehydration reaction in the synthesis of a fat

Fat molecule (triacylglycerol) LE 5-11b Ester linkage Fat molecule (triacylglycerol)

Properties of Fats Hydrophobic Fatty acids H2O molecules form hydrogen bonds with each other and EXCLUDE fatty acid chains--> Fats separate from H2O (like oil & vinegar) Fatty acids variable chain length (often 16-18 carbons)

Saturated fat - refers to saturated fatty acid chains - carbons contains maximum number of hydrogens - results in 100% single bonds (no double bonds) - more linear, packs tightly to form solid Tend to be from animals

Saturated or unsaturated? LE 5-11b Saturated or unsaturated? Ester linkage Fat molecule (triacylglycerol)

LE 5-12a Butter Stearic acid Saturated fat and fatty acid.

Unsaturated fat -contains unsaturated fatty acids -carbon-carbon double bonds (>1) -irregular hydrocarbon conformation -poor packing -forms liquids (oils) at room temperature Tend to be from plants and fish

Other liquid fats (unsaturated)? LE 5-12b Olive oil Other liquid fats (unsaturated)? Oleic acid cis double bond causes bending Unsaturated fat and fatty acid.

Phospholipids Structure Fatty acids= Hydrophobic tail two fatty acids bonded to glycerol through ester linkage Phosphate bonded to third hydroxyl group of glycerol Fatty acids= Hydrophobic tail Phosphate and other groups= hydrophilic head Draw schematic

Choline Hydrophilic head Phosphate Glycerol Hydrophobic tails LE 5-13 Choline Hydrophilic head Phosphate Glycerol Hydrophobic tails Fatty acids Hydrophilic head Hydrophobic tails Structural formula Space-filling model Phospholipid symbol

If many phospholipids were mixed in H2O into what structures would they self-assemble? Micelle (draw) - Detergents Bilayer (draw) -Cell membranes

Cellular membrane: Phospholipid Bilayer LE 5-14 Cellular membrane: Phospholipid Bilayer WATER Hydrophilic head Hydrophobic tails WATER

Steroids Structure Examples and Diverse Functions - Hydrophobic molecules made of 4 fused hydrocarbon rings Examples and Diverse Functions Cholesterol Component of animal cell membranes Building block for steroid sex hormones such as Estrogen, testosterone, progesterone High levels--> contribute to heart disease

Cholesterol

estradiol testosterone

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Ch 7 Membrane Structure and Function

Cellular membrane -overall functions - Boundary between intracellular compartments, living cells, and abiotic environment Selectively permeable Some molecules cross membranes more readily than others

Membrane Structure Predominant constituent: phospholipids Amphipathic molecules: hydrophobic AND hydrophilic Dispersed protein components Membrane organization and properties described by: Fluid Mosaic Model Singer and Nicolson 1972

Organization of membrane phospholipids LE 7-2 Organization of membrane phospholipids WATER Hydrophilic head Hydrophobic tail WATER

Mosaic: something made of small pieces

Mosaic: Proteins dispersed among phospholipids in membrane: LE 7-3 Mosaic: Proteins dispersed among phospholipids in membrane: Hydrophilic region of protein Phospholipid bilayer Hydrophobic region of protein

Imaged by EM Freeze-fracture studies of the plasma membrane Frozen membrane split along the middle of the phospholipid bilayer using a knife Imaged by EM Supports mosaic part of model

Extracellular layer Proteins Knife Plasma membrane Cytoplasmic layer LE 7-4 Extracellular layer Proteins Knife Plasma membrane Cytoplasmic layer Extracellular layer Cytoplasmic layer

The Fluidity of Membranes Phospholipids move laterally within the bilayer Some membrane proteins also drift laterally Rarely does a phospholipid flip-flop transversely across the membrane

Movement of phospholipids LE 7-5a Lateral movement (~107 times per second) Flip-flop (~ once per month) Movement of phospholipids

Cool temp: membranes switch from fluid to more solid state Effects of Temperature on membranes Cool temp: membranes switch from fluid to more solid state Solidification depends on type of lipid What property of lipids would favor liquid versus solid state?

Degree of saturation of fatty acid tails LE 7-5b Degree of saturation of fatty acid tails Fluid Viscous Unsaturated hydrocarbon tails with kinks Saturated hydro- carbon tails Membrane fluidity

Tends to moderate effects of temp. on membrane state Steroid cholesterol also component of membranes Tends to moderate effects of temp. on membrane state At warm temperatures (such as 37°C), restrains movement of phospholipids At cool temperatures, maintains fluidity by preventing tight packing

Cholesterol within the animal cell membrane LE 7-5c Cholesterol Cholesterol within the animal cell membrane

Movement of membrane proteins Can drift within the bilayer Proteins much larger than lipids--> move more slowly Cell fusion studies support fluidity of membrane proteins

Membrane proteins Mouse cell Mixed proteins after 1 hour Human cell LE 7-6 Membrane proteins Mouse cell Mixed proteins after 1 hour Human cell Hybrid cell

Membrane Proteins and Their Functions Proteins determine most of the membrane’s specific functions Peripheral membrane proteins not embedded attached to extracellular or cytoplasmic surface Integral membrane proteins penetrate the hydrophobic core of bilayer often span the membrane

LE 7-7 Fibers of extracellular matrix (ECM) Glycoprotein Carbohydrate Glycolipid EXTRACELLULAR SIDE OF MEMBRANE Cholesterol Microfilaments of cytoskeleton Peripheral proteins Integral protein CYTOPLASMIC SIDE OF MEMBRANE