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 – 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

LE 5-11a

Fatty acid (palmitic acid) Glycerol Dehydration reaction in the synthesis of a fat

LE 5-11b

Ester linkage Fat molecule (triacylglycerol)

Properties of Fats

• Hydrophobic • H 2 O molecules form hydrogen bonds with each other and EXCLUDE fatty acid chains--> Fats separate from H 2 O (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

LE 5-11b

Ester linkage

Saturated or unsaturated?

Fat molecule (triacylglycerol)

LE 5-12a Butter

Saturated fat and fatty acid.

Stearic 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

LE 5-12b Olive oil Other liquid fats (unsaturated)?

Unsaturated fat and fatty acid.

cis double bond causes bending Oleic acid

Phospholipids

• Structure – 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

LE 5-13

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

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 Cellular membrane: Phospholipid Bilayer

WATER Hydrophilic head Hydrophobic tails WATER

Steroids

• Structure - 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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