Lipids C, H, and O but C:H ratio is 1:2 Much less O than CHO Eg. Lauric acid C 12 H 24 O 2 Energy source and structural component of cells Intake of fat sol vits dependent on fat intake Many classes –Fatty acids –Eicosanoids –Glycerides –Steroids –Phospholipids –Glycolipids

Fatty acids Long hydrocarbon chains with carboxyl group (COOH) at one end Carboxyl end likes water (hydrophillic), other end (methyl group –CH 3 ) hydrophobic. Saturated –Each C atoms has 4 single covalent bonds Unsaturated (mono- or poly-) –C = C double bonds

Eicosanoids Derived from the fatty acid Arachidonic acid (essential) 2 major classes: –Prostaglandins: unusual short chain fatty acids containing a 5C ring structure. Produced by most body tissues and often act locally eg. –Released by uterus help trigger start of labor –Stimulate nerve ending  pain sensation –Leukotrienes Produced by cells involved with coordinating responses to injury/disease.

Tryglycerides 3 functions: –Energy stored until needed –Insulation –Protection eg. Around kidney Lipid droplets in cells absorb lipid-sol vitamins, drugs, or toxins

Steroids Large lipid molecules that share a basic ring structure Functions: –Cell membrane (cholesterol) –Sexual function –Regulation of metabolism (corticosteroids) and mineral balance (calcitriol) –Formation of bile salts – digestion/absorption of lipid Chol. obtained from diet or synth in body

Phospholipids and glycolipids Synthesised by cells from fatty acids Phospholipid –PO 4 3- attached to a diglyceride and non-lipid molecule Glycolipid –CHO attached to diglyceride Hydrophobic tails, hydrophillic heads Structural lipids (along with cholesterol) due to function in cell membrane

TABLE 2-5 Representative Lipids and Their Functions in the Body Lipid Type Example(s)Primary Function(s) Remarks Fatty acids Lauric acidEnergy source Absorbed from food or synthesized in cells; transported in the blood for use in many tissues Glycerides Monoglycerides, Energy source, Stored in fat deposits; must be broken down diglycerides, storage, insulation, to fatty acids and glycerol before they can triglycerides physical protection be used as an energy source Eicosanoids Prostaglandins, Chemical messengers Prostaglandins are produced leukotrienes coordinating local in most body tissues cellular activities Steroids CholesterolComponent All have the same carbon ring framework of cell membranes, and bile; hormones Phospholipids, Structural components Derived from fatty acids and nonlipid components glycolipidsof cell membranes

Lipid digestion Lingual and pancreatic lipase digests TG’s into fa’s and glycerol Duodenum – fat in lg lipid globules Bile acid emulsify fats into smaller droplets  micelles Micelles absorbed through villi

Fatty acid absorption FAs diffuse across membrane into epithelial cell where reform into TGs TG’s combine with cholesterol or phopholipid  chylomicrons  lacteal Short and medium chain fa’s are more water sol – diffuse into blood, bind to albumin  liver in hpv

Transport of fats ‘Free’ fatty acids mostly bound to albumin in plasma; TG’s and cholesterol transported by lipoproteins –Chylomicrons –VLDL –LDL –IDL –HDL

Cholesterol and lipid processing by the liver

Fat in the diet ~38% of Western diet ~15%saturated fat Most cholesterol from animal sources, + shellfish Body synthesises its own cholesterol LDL promotes development of atheroslerosis  CVD –Reduce sat fat in diet –Exercise –Cholesterol lowering drugs HDL protective

Cis- vs Trans- fatty acids Different in their double bond configuration Most natural fatty acids contain cis- Processed often contain trans- Trans-fatty acids resemble saturated fatty acids Butter or margarine? –Same energy density –Margarine – oils are hydrogenated and ~20% become trans (cf 7% in butter)  increase LDL and decrease HDL –But no cholesterol in margarine, wheras butter contain cholesterol –Butter also increases LDL but does not lower HDL –Total fat reduction is probably the answer –Monounsaturated seems to reduce risk –As do omega-3 from fish