Lipids Highly diverse structures Unifying property Hydrophobic: little to no affinity to water Contains hydrocarbons, which form nonpolar covalent bonds Do not form polymers Most important in biological context –Fats –Phospholipids –Steroids

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

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

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

Hydrophobic H 2 O molecules form hydrogen bonds with each other and EXCLUDE fatty acid chains--> Fats separate from H 2 O Properties of Fats Fatty acids variable chain length (often carbons)

Saturated fats - refer to saturated fatty acid chains -contain maximum number of hydrogens - result in 100% single bonds - more linear, pack tightly to form solid Tend to be from animals

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

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

LE 5-12b Unsaturated fat and fatty acid. Oleic acid cis double bond causes bending

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

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

If many phospholipids were mixed in H 2 O into what structures would they self-assemble? 1.Micelle (draw) - Detergents 2.Bilayer (draw) -Cell membranes

LE 5-14 WATER Hydrophilic head Hydrophobic tails WATER

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

Cholesterol

estradiol testosterone

Pardon me. I think I missed something…

Ch 7 Membrane Structure and Function

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

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

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

Mosaic: something made of small pieces

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

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

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

The Fluidity of Membranes Phospholipids move within the bilayer Most of the lipids, and some proteins, drift laterally Rarely does a molecule flip-flop transversely across the membrane

LE 7-5a Lateral movement (~10 7 times per second) Flip-flop (~ once per month) Movement of phospholipids

Cool temp: membranes switch from fluid to solid state Solidifications depends on the types of lipids What propertyof lipids would favor solid versus liquid state? Effects of Temperature on membranes

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

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 Steroid cholesterol also component of membranes

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

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

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

Membrane Proteins and Their Functions Proteins determine most of the membrane’s specific functions Peripheral membrane proteins –not embedded Integral membrane proteins – penetrate the hydrophobic core of bilayer –often span the membrane

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