Lipids

• C, H , and O but C:H ratio is 1:2• Much less O than CHO• Eg. Lauric acid C12H24O2

• 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 –CH3) 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

– PO43- 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 acid Energy 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 Cholesterol Component All have the same carbon ring framework

of cell membranes,

and bile; hormones

Phospholipids, Structural components Derived from fatty acids and nonlipid components

glycolipids of 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