Lecture Five
Lipids
-Organic compounds (CnHnOn) that contains more C and H in proportion to O
than does CH2O
-Insoluble in water, but soluble in organic solvents (ether, acetone, benzene)
-Supplies 40% of the calories in American diets
-Source of essential fatty acid
-Necessary for fat soluble vitamins A, D, K and E
-Concentrated form of energy
-1g of fat = 9.45kCal
-1g of protein or CH2O = 4.1 kCal
-On average  2.25 times more energy in fat than CH2O or protein
-Important for hibernating animals
-Simple Lipids
-Esters of fatty acids and alcohol (glycerol)
-Fats and oils = esters of fatty acids and glycerol
-Waxes = esters of fatty acids and alcohol (not glycerol)
-Compound Lipids
-Esters of fatty acids, also containing nonlipid substances (P, CH2O,
proteins)
-Phospholipids (phosphoric acid, N) membranes,
transport/emulsification
-Glycolipids (CH2O, N)
-Lipoproteins carriers in blood and tissues (LDL, HDL, VHDL)
-Derived Lipids
-Substances derived from simple and compound lipids by hydrolysis
-Sterols
-Lipids with complex phenanthrene type ring structure
-Terpenes
-Isoprene type structures
-Structure of Lipids
-Fatty Acids
-Carbon chains from 2-24 in length
-Even numbered straight chained in most animal tissue
-Some branched in ruminants
-Carboxyl group at the end of each
-RCOOH general structure (R stands for fatty acid chain)
-CH3CH2COOH is acetate
-Double bond vs. H Saturation
-Stearic C18:0  number of double bonds
-Linolenic C18:3 number of double bonds
-Isomers
-Cis
-Trans (margarine, other hydrogenated fats)
-Glycerol is an alcohol
-Mono, Di, and triglycerides are esters of fatty acids and glycerol
-Mono, Di, and triglycerides
-Typically are mixed triglycerides (98%)
-Chain length, degree of saturation determines physical properties
-TG of C10:0 or longer = solid at room temperature
-TG of less than C10 = liquid at room temperature
-TG with each fatty acid saturated = solid
-TG with more unsaturated fatty acids = liquid
-Fats can have 10 or more different fatty acids
-Lipids
-Phosopholipids
-Usually contain fatty acids (hydrophobic), phosphoric acid
(hydrophilic), a glycerol, a nitrogenous base
-Higher in unsaturated fatty acids than lipids in adipose tissue
-Widely dispersed in body fluids
-Emulsifying properties that help to function in lipid transport
-Sterols
-Phenanthrene type ring
-Cholesterol, ergosterol, 7-dehydrocholesterol, androgens,
estrogens, progesterone
-Lipid Functions
-Energy supply
-2.25 times that of CH2O and protein
-Source of essential fatty acids (EFA)
-Can not be synthesized in adequate amounts
-Linoleic Acid (C18:2) and linolenic acid (C18:3)
-Arachidonic acid (C20:4) can be synthesized from linoleic
acid
-Involved in maintenance of skin integrity in nonruminants
-Young ruminants require essential fatty acids in diet (just like non
ruminants)
-Carriers of fat soluble vitamins
-Vitamins A, D, E and K
-Absorption is a function of digestion and absorption of fats
-Mixed micelles containing monoglycerides and FFA’s
higher rate of vitamin uptake
-Source as insulation and protection as well as heat generation
-Lipid Absorption
-Site of major fat processing—upper small intestine
-Fats (mostly triglycerides) mix with bile and pancreatic and intestinal
secretions
-Bile salts act as emulsification agents (detergent like action)
-Particle size decreases increasing surface area and exposure to
lipases
-Lipases attach fatty acid in 1 and 3 positions result in beta
monogylcerides and free fatty acids
-Monoglycerides + FFA + bile salts + phospholipids + cholesterol=mixed
micelles
-Bile Salts
-Secreted in large quantities, reabsorbed in jejunem and
ileum, recycled in liver
-Facilitate digestion and absorption of lipids
-Absorption of fat soluble vitamins
-Cholesterol absorption
-Mixed micelles combine with cholesterol and fat soluble vitamins =
larger mixed micelles
-Main site of absorption is upper jejunem, some absorption in duodenum
and ileum
-Upon entering mucosal cell
-Fats are reassembled into triglycerides
-Protein coating takes place to form chylomicrons (triglycerides,
phospholipids, cholesterol, esters, and protein)
-Chylomicrons enter lacteals via intercellular space lymphatic
system  thoracic duct
-Mammals absorb long chain fatty acid lipids via lymph (chickens
absorb directly into portal blood)
-Transport of Lipids
-Blood lipids
-Chylomicrons
-Lipids arising from mobilized depot stores
-Lipids synthesized in body tissues (liver and adipose)
-Transported as lipoproteins
-4 Major Classes
-Chylomicrons (highest ratio of lipids to proteins)
-VLDL (very low density by lipoproteins)
-LDL
-HDL
-Lipid Deposition
-All tissues store triglycerides
-Adipose tissues are most significant sites
-Can synthesize TG from CH2O and oxidize fats
-TG are ready source of energy so, there is continous triglyceride
deposition and mobilization
-Energy intake in excess results in net deposition of TG. Reverse is also
true
-Fat depot=fatty acid characteristics for each animal
-Non ruminants= dietary fatty acid influences fat depot
-Ruminants= less responsive, bypass fats
-Fatty Acid and TG to Metabolism
-Major sites of lipid metabolism
-Liver
-Mammary gland
-Adipose tissue
-Liver (example)
-Synthesis of :
-Fatty acids from CH2O and amino acids
-Cholesterol
-Phospholipids
-Lipoproteins
-Ketones
-Degradation of:
-Fatty acids, phospholipids
-Saturation, desaturation, lengthening, shortening, deposit
of liver lipids
-Biosynthesis of fatty acids
-Active in adipose, liver and mammary tissues
-Begins in Acetyl-CoA
-Assembled in 2 carbon units
-Animal tissue synthesizes up to 16 carbons
-Desaturation in tissue is limited
-Ruminant:
-Glucose propionate lactate acetate Acetyl-CoA
-Biosynthesis of Triglycerides
-Acetyl-CoA + alpha-glycerol phosphate phospholipid + Acyl-CoA
diglyceride + Acyl-CoA triglyceride
-Triglyceride Catabolism
-Adipose tissue
-Composed primarily of adipose tissue
-Dynamic tissue= synthesis and degradation of triglycerides
-Lipoprotein lipase= hydrolysis of TG
-Synthesized in many tissues
-Activity high in fed state, low in fasted state
-Activity under hormonal control
-Lypolysis is stimulated by: beta-adrenergic agonists
(paylean), adrenocortcotropins, somatotropin (GH)
-Inhibited by: prostaglandins and insulin
-Lypolysis is “break down of lipids”
-Control of net fat accretion involves complex regulatory systems
that include lypolysis and lipogenesis
-Fatty Acid Catabolism
-Fatty acids released from hydrolysis=transported to tissues as an
oxidative energy source
-Oxidation (beta oxidation and TCA cycle) occurs in the mitochondria
(skeletal muscle, liver, cardiac muscle, adipose tissue, etc.)
-Beta oxidation stepwise enzymatic removal of 2 carbon units (AcetylCoA) to be used for resynthesis of fatty acids, synthesis of steroids or
ketones, entry into TCA cycle
-Not reverse of synthesis process
-Total energy with oxidation of a LCFA comes from both beta oxidation
and Acetyl-CoA oxidation in TCA cycle
-Steroid Metabolism
-Cholesterol = most abundant sterol and precursor to most others
-Biosynthesis of Acetyl-CoA
-Partially controlled by dietary intake
-Cholesterol excreted in bile
-Used for sterol synthesis; progesterone, ACTH, testerone,
estrogen
-Phospholipid Metabolism
-Lecithin (phosphatidyl choline) is most abundant in animal tissue
-Ketone Metabolism
-Formation of ketones is continous
-Used as energy source in skeletal muscle and other peripheral tissue
-Overproduction occurs in:
-Disorders: diabetes mellitus
-Low CH2O intake
-Abnormalities in Lipid Metabolism
-Fatty Livers
-Dairy cattle in negative energy balance
-Associated with excessive fat mobilization from adipose tissue
-Fat deposited in liver (5%) slower net loss
-Transition period important
-Feeding protected choline
-Ketosis
-Overly fat animals, often seen in dairy cattle
-Rapid mobilization of fat depot
-Reduced intakes
-Lack of ability to metabolize Acetyl-CoA in TCA cycle fast
enough
-Acetyl-CoA Acetoacetic acid acetone and B-hydroxybutric
acid
-Obesity
-Over consumption of calories is a factor
-Genetics plays a major role
-Lipogenic enzyme activity in adipose tissue of obese
animals higher
-Net deposition is greater than normal
-Cell size and number
-Vary with species and individuals
-Proliferation can occur postnatally