Lipid Chemistry

lipids made up of C, H, and O are insoluble in water but

soluble in organic solvents

one gram of typical lipid yields 9.45 kcal gross energy (heat) when completely combusted

1g of carbohydrate = 4.2kcal

fats produce approximately 2.25 times more energy than

carbohydrates

lipids have a wide variet of sizes and shapes

diverse group

the hydrophobic head of lipids hates water, while the hydrophili tail 

loves water

one gram of fat is how much gross energy?

9.45 kcals

one gram of CHO has how much gross energy?

4.2 kcals

plants sources of lipids in diets

oilseeds (soybeans, cottonseed, canola: 18-25% lipid), grain (corn, mila, wheat: 2-4 % lipid)

animals sources of lipids in diets are

tallow (beef, ruminant), oil

sources of lipids in human diet

corn, oil, soybean oil, meat, lard

by-pass fats (rumen by-pass or rumen protected

Ca + fat = avoid rumen microbial fermentaion to make it to S.I. intact, fat with a protein matrix coating

normal digestibility of fat is

80-90%

classification of lipids

simple, compound, lipoproteins, derived, fatty acids,

simple lipids are

true fat and waxes

true fat

esters of fatty acids with the alcohol glycerol (sometimes called triglycerides (TG) or triacylglycerides (TAG)

waxes

esters of fatty acids with alcohol other than glycerol (simple and relatively non-polar 

compound lipids

esters contain groups in addition to an alcohol of fatty acids

examples of compound lipids

phospholipids, glycolipids, lipoproteins

phospholipids contain

phosphoric acid and N (part of body cell membrane, types: lecithin (cell membrane) and sphingomyelin (component of the myolin sheath which lines nerves cells) 

glycolipids contain

contain carbohydrate and nitrogen byy no phosphoric acid (cerebrosides)

cerebrosides are a component of

myolin sheath and also the white matter of the brain

lipoproteins are lipids bound to

proteins in blood and other tissue; includes chylomicrons, VLDL, LDL, and HDL 

chylomicrons are formed

inside small intestine mucosal cells (enterocytes)

chylomicrons are majority of the fat carried

transported out of small intestine

VLDL (very low-density lipoproteins) contain

high levels of triglycerides

VLDL (very low-density lipoproteins) transport

lipids from liver to extra hepatic tissues

VLDL (very low-density lipoproteins) tissue cells secrete

lipoprotein lipase (LPL) which breaks down TG to free fatty acids and glycerol, leaving LDLs

HDL (high density lipoproteins) are high in

protein, low in lipids

HDL (high density lipoproteins) are produced

in liver and small intestines

HDL (high density lipoproteins) will bind excess

cholesterol and carry back to liver for excretion

desirable blood concentration in humans:

-total cholesterol → less than 200 mg/ 100 mL (reflects low risk of heart disease)

-HDL → over 40mg/ 100 mL

-total cholesteral to HDL cholesterol → not over 5:1 ratio

examples of derived lipids

sterols and fatty acids

sterols (ring stuctures)

cholesterol is the most abundant (found only in animal tissue), precursur for other sterol compounds (7-dehydrocholesterol (Vit D, bile salts, steroid hormones))

fatty acids physical properties 

solubility in water, melting point, degree of saturation 

fatty acid solubility in water

increased chain length = reduced solubility; more than 8 C = insoluble in water 

melting point of fatty acids 

increased chain length = increased melting point

degree of saturation (number of double bonds) for fatty acids

increased unsaturation = reduced melting point; overrides effects of chain length

fatty acid susceptibility to oxidation means

increased unsaturation = increased oxidation, significance = rancidity and free radicals (plaque in arteries; caner; white muscle disease), prevention = hydrogenation and antioxidants (natural Vit. E or synthetic) 

essential fatty acids (EFA) are

linoleic acid (18:2); linolenic acid (18:3); arachadonic acid (20:4)

physiological needs for EFA are part of

lipid/protein structure of cell membranes; synthesis of prostaglandins (hormone-like compounds) which control blood pressure, smooth muscle contractions, and have a role in reproduction 

EFA deficiency leads to

skin lesions (scaly, flaky skin), growth failure, poor feather development,diarrhea in humans 

EFA requirement is 1% of

total kcal intake should be EFA

cholesterol is the precursor for steroid hormone production and is

important for cell membranes, used in vitamin D3 formation

steroids include

sterols, bile acids, adrenal corticoids, sex steroids

main classes of eicosanoids 

prostaglandins, thromboxanes, leukotrienes 

eicosanoids are all synthezised from

arachidonic acid (20C)

saturated fat means

single bonds make up structure

unsaturate fat means

double bonds on structure

physical and chemical characteristics of lipids are

degree of saturation, number of carbons (chain length), and position of the double bonds 

degree of saturation

TAGs containing mostly unsaturated FAs are liquid at room temperature

number of carbons (chain length)

longer chains (more carbons) tend to be solid at RT

position of the double bonds alter

the shapes of the fatty acids

exeption to melting point

acetic acid has a melting point higher than predicted by carbon number

all saturated fatty acids in beef (14, 16, and 18 carbons) are 

solids at room temperature 

all polyunsaturated fatty acids are liquids are

liquids at room temperature

for most animals the MP of lipids ranges

22-44 degrees celcius

MP is determined by

fatty acid composition

fatty acid compostion is determined by diet and genetics

lipids of tissues from monogastrics fed unsaturated fatty acids closely resemble the fatty acid composition of the diet, composition of lipids of tissues from ruminants are determined by diet (limited efffect) and the activity of the tissue desaturases 

stucure of lipids

cell membranes: barrier

signaling of lipids

communication between and within cells

sources of energy and source of

heat, insulations, and protection for the animal body

linoleic acid and lenolenic acid apparently cannot by synthesized by

animal tissues, or at least not in sufficient amounts to prevent pathological changes, and so must be supplied in the diet 

arachidonic acid can be synthesized from linoleic acid, and therefore is

required in the diet only in linoleic cacid is absent 

delta system 

numbers from the carboxyl end to the first unsaturated carbon (standard biochemical technique)

“N minus” system is

numbers from the terminal methyl carbon to the first unsaturated carbon, “subtracts” those carbons, and places these numbers in paretheses 

omega system

numbers from the terminal methyl carbon to the first unsaturated carbon

nomenclature systems

delta system, “n minus” system, omega system, trivial names, geneva system 

defficiency or abnormal metabolism of lipids (or deficiency of certain fatty acidds in monogastric diets) results in

skin lesions, hair loss, poor feathering in chicks, and reduced growth or reproductive rate

ketosis is

insufficienct dietary energy intake in high-producing animals may cause catabolism of body reserves needed for energy

if ketosis steps do not occur normally, the two carbon fragments from fat catabolism accumulate and produce

toxic blood levels of ketone bodies (acetone, acetoacetic acid, and beta-hydroxybutyric acid) 

ketosis is a phsiological disorder that is most common in

dairy cattle during early lactation or sheep during gestation

fattly livers are a possible result of

abnormal liver function is the accumulation of lipids in the liver

fatty livers may arise from

high dietary fat or cholesterol intake, increased liver lipogenesis, increased mobilization of lipids from adipose tissue, or various other deficiencies or abnormalities