Lipids and Carbohydrates

Part 1: Lipid Characteristics Lipid = a compound that is insoluble in water, but soluble in an organic solvent (e.g., ether, benzene, acetone, chloroform) “lipid” is synonymous with “fat”, but also includes phospholipids, sterols, etc. chemical structure: glycerol + fatty acids

Lipid Molecule

Nutritional Uses of Lipids We already know that lipids are concentrated sources of energy (9.45 kcal/g) other functions include: 1) provide means whereby fat-soluble nutrients (e.g., sterols, vitamins) can be absorbed by the body 2) structural element of cell, subcellular components 3) components of hormones and precursors for prostaglandin synthesis

Lipid Classes simple: FA’s esterified with glycerol compound: same as simple, but with other compounds also attached phospholipids: fats containing phosphoric acid and nitrogen (lecithin) glycolipids: FA’s compounded with CHO, but no N derived lipids: substances from the above derived by hydrolysis sterols: large molecular wt. alcohols found in nature and combined w/FA’s (e.g., cholesterol)

Saturated vs. Unsaturated Fatty Acids saturated: the SFA’s of a lipid have no double bonds between carbons in chain polyunsaturated: there is/are more than one double bond(s) in the chain most common polyunsaturated fats contain the polyunsaturated fatty acids (PUFAs) oleic, linoleic and linolenic acid unsaturated fats have lower melting points stearic (SFA) melts at 70oC, oleic (PUFA) at 26oC

Fatty Acids Commonly Found in Lipids

Saturated vs. Unsaturated Fats saturated fats tightly packed, clog arteries as atherosclerosis because of double bonds, polyunsaturated fats do not pack well -- like building a wall with bricks vs. irregular-shaped objects plant fats are much higher in PUFA’s than animal fats

Saturated vs. Unsaturated FA’s Plant vs. Animal Fat

Lipid Digestion/Absorption Fats serve a structural function in cells, as sources of energy, and insulation the poor water solubility of lipids presents a problem for digestion: substrates are not easily accessible to digestive enzymes even if hydrolyzed, the products tend to aggregate to larger complexes that make poor contact with the cell surface and aren’t easily absorbed to overcome these problems, changes in the physical state of lipids are connected to chemical changes during digestion and absorption

Lipid Digestion/Absorption Five different phases: hydrolysis of triglycerides (TG) to free fatty acids (FFA) and monoacylglycerols solubilization of FFA and monoacylglycerols by detergents (bile acids) and transportation from the intestinal lumen toward the cell surface uptake of FFA and monoacylglycerols into the cell and resynthesis to triglyceride packaging of TG’s into chylomicrons exocytosis of chylomicrons into lymph

Enzymes Involved in Digestion of Lipids lingual lipase: provides a stable interface with aqueous environment of stomach pancreatic lipase: major enzyme affecting triglyceride hydrolysis colipase: protein anchoring lipase to the lipid lipid esterase: secreted by pancreas, acts on cholestrol esters, activated by bile phospholipases: cleave phospholipids, activated by trypsin

What about Bile??? These are biological detergents synthesized by the liver and secreted into the intestine they form the spherical structures (micelles) assisting in absorption hydrophobic portion (tails of FA) are located to the inside of the micelle, with heads (hydrophillic portion) to the outside they move lipids from the intestinal lumen to the cell surface absorption is by diffusion (complete for FA and monoglycerides, less for others)

Factors Affecting Absorption of Lipids amount of fat consumed ( fat =  digestion =  absorption) age of subject ( age =  digestion) emulsifying agents chain length of FA’s (> 18C =  digestibility) degree of saturation of FA ( sat =  digestibility) overheating and autooxidation (rancidification at double bond) optimal dietary calcium = optimal FA absorption (high Ca =  absorption)

Lipid Metabolism/Absorption short chain FA’s are absorbed and enter the portal vein to the liver those FA’s with more than 10 carbons are resynthesized by the liver to triglycerides they are then converted into chylomicrons and pass to the lymphatic system some FA’s entering the liver are oxidized for energy, others stored blood lipids: 45% phospholipids, 35% triglycerides, 15% cholestrol esters, 5% free FA’s

Lipid Digestion/Absorption I

Lipid Digestion/Absorption II

Characteristics of Fat Storage Most of the body’s energy stores are triglycerides storage is in adipose, source is dietary or anabolism (synthesis) from COH or AA carbon skeletons remember obesity? adipose can remove FA’s from the blood and enzymes can put them back

Fatty Acid Nomenclature Nomenclature reflects location of double bonds also used are common names (e.g., oleic, stearic, palmitic) linoleic is also known as 18:2 n-6 this means the FA is 18 carbons in length, has 2 double bonds, the first of which is on the 6th carbon arachidonic = 20:4 n-6

Essential Fatty Acids Only recently determined as essential (1930) body can synthesize cholesterol, phospholipids research: same as AA’s but via addition (EFA’s added improved growth, NEFA’s didn’t) requirement determined by depleting fat reserves of subject animal: difficult

Essential Fatty Acids (fish) Most NEAA found in marine food webs Essential fatty acids (to date): linoleic (18:2 n-6; terrestrials; fish - not really) linolenic (18:3 n-3; terrestrials; fish) arachidonic (20:4 n-6; marine maybe) eicosopentaenoic acid (20:5 n-3, marine) docosohexaenoic (22:6 n-3, marine) Why? Because elongation beyond 18 carbons is very difficult in marine fish (lack pathways) actual EFA requirement is a matter of whether the fish is FW/SW or WW/CW

Essential Fatty Acids (most animals) salmonids need n-3 FA’s for membrane flexibility in cold water trout can elongate and desaturate n-3 FA’s Linoleic acid (18:2 n-6) is the most essential addition of arachidonic is also helpful in deficient diets, but can be synthesized from linoleic (maybe sparing effect) EFA’s, like EAA’s, must be dietary

Essential Fatty Acids LINOLEIC CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH LINOLENIC CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOH 18:3 n-3 EICOSOPENTAENOIC ACID CH3CH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CH(CH2)3COOH 20:5 n-3 DOCOSOHEXAENOIC ACID - YOU CAN DO THIS ONE!

Lipid Requirement: crustaceans Dietary lipid partially provided by practical feed ingredients, also by “pure” oils (e.g., fish oils) best growth/survival at 5-8% of diet “best level” depends on quality and quantity of dietary protein, other energy sources, oil quality abnormally high levels = reduced growth, reduced consumption, deposition in midgut gland

Lipid Requirement: crustaceans High dietary fat will insure adequate energy, but could reduce intake of other essential nutrients shrimp fed 15% dietary oil (cod liver) had reduced growth rate compared to those fed 7.5% growth trials also show that marine sources of lipids superior to plant sources however: mixture does better (3:1 ratio)

Lipid Digestibility: crustaceans Lipid digestion (tripalmitate) by lobster occurs in about 8-12 hours about 80% for most when lipid is 8% of diet FA’s have high digestibilities: 90% digestibility of HUFA’s decreases with chain length digestibility of one FA affected by another growth response to lipid sources is really a question of FA deficiencies

Crustacean Fatty Acids Type 1) those synthesized from acetate, includes all even-numbered, straight chains palmitic acid, can be desaturated by crustaceans (i.e., one double bond) Type 2) unusual FA’s w/odd-numbered carbon chains Type 3) EFA’s of the linoleic and linolenic groups having more than one double bond type 3’s cannot be synthesized by shrimp

Freshwater vs. Saltwater Crustaceans Marine crustaceans have more HUFA’s than freshwater species HUFA = >20 carbons, > 3 double bonds marine = more linolenic type than linoleic fw = more linoleic, less linolenic

Lipid/FA Biosynthesis: crustaceans Crustaceans have little ability at synthesis if fed acetate, most converted to monounsatured FA’s, no chain elongation less than 2% went to PUFA formation (linoleic, linolenic) thus, these FA’s as well as others (docoso- hexanoic, eicosopentanoic, arachidonic) must be in diet

Lipids as Crustacean Energy Sources Largely, n-6 FA’s (linoleic) used for energy as temperature drops, requirement for monounsaturated and PUFA’s increases change in temperature = change in diet cold water species = increased dietary HUFA’s maturation animals: increased requirement for 20:4 n-6, 20:5 n-3 and 22:6 n-3 for proper spawning

Part 2: Carbohydrate Characteristics From: Lovell; D’Abramo et al.

General Comments Carbohydrates often written as “COH” much of what we need to know about them, besides their structure, was covered in “Bioenergetics, Parts 1&2” here, we cover structure

Carbohydrate Structure Basic chemical structure consists of sugar units found as aldehydes or ketones derived from polyhydric alcohols contain: C, H, O often shown as aliphatic or linear structures, but exist in nature as ringed structures

Glucose Structure O C-H H- C-OH HO-C-H H-C-OH CH2OH CH2OH O H H OH H Haworth perspective

Carbohydrate Classification Usually by the number of sugar units in the molecule: monosaccharides (glucose) disaccharides (2 units) maltose (2 glucose units) sucrose (glucose + fructose) polysaccharides (long chain polymers of monosaccharides most important polysaccharides to animals are starch and cellulose

Starch and Cellulose CH2OH CH2OH O O H H H H starch OH H OH H O O O H

Starch and Cellulose Starch contains -D-glucose linkage Cellulose has a -D-glucose linkage we store starch in muscle tissues as glycogen, peeled off by enzymes when needed cellulose is primary component of plant tissue, largely indigestible to monogastrics must have enzyme, “cellulase”