5: Lipids

phosphoglycerides

lecithins, cephalins

glycolipids

glucolipids, galactolipids

glycerol based, compound lipids

lipoproteins, glycolipids, phosphoglycerides

what carbon does phosphorylation of TAGs ALWAYS occur on?

C3

most nutritionally significant lipid

triacylglycerols (TAGs)

butterfat sn positions

• Sn-1: C18:0 (stearic acid)

• Sn-2

• Sn-3: C4:0 (butyric acid)

phytosterols origin

plants

zoosterols origin

animals

cholesterol

zoosterol synthesized from acetate in liver

compound lipids

no glycerol backbone

glycolipids

CHO + lipid; plants

lipoproteins

lipid + protein; transports lipids in body

phospholipids

PO4 + lipid; cell membranes

lecithin

most abundant of cell membrane; secreted in bile; body store of choline (important methyl donor)

vitamin D synthesis pathway

7-dehydrocholesterol → cholecalciferol (D3) → liver → kidney → 1-25-di-OH-Vitamin D3

cholecalciferol (D3)

inactive precursor of vitamin D; converted from 7-dehydrocholesterol in skin by UV

do natural FAs have even or odd numbers of carbons?

even

how are odd chain FAs formed?

due to absorption of rumen microbes

biohydrogenation

converts unsaturated FAs to saturated by adding H

what happens to unsaturated fats in the rumen?

become saturated - major is C18:0 from C18:2 and C18:3

delta in structure naming

exact position of each double from carboxyl

omega structure naming

first double from methyl

saturated FA names

• acetic - 2

• propionic - 3

• butyric - 4

• palmitic - 16

• stearic - 18

• arachidic - 20

monoenes

unsaturated 18C FA with one double bond

dienes

more than one double bond with 18 C - poly-unsaturated FA

monoenes names

omega-9: oleic acid, elaidic acid

most abundant monoene

oleic acid

dienes names

linoleic acid - omega 6

primary source of dienes

plant oils

canola meal is a good source of…

protein and oleic acid

soybean and sunflower meal is a good source of…

protein and linoleic acid

trienes names

linolenic acid, omega-6 and omega-3

where are trans FAs formed?

in rumen

main trans 18:1 FA in rumen

vaccenic acid

less than this number of carbons is liquid

12

linoleic family

w-6; skin and RBCs

linolenic family

w-3; eye and nervous system

oleic family

w-9; not abundant, made in ESSENTIAL FA deficiency

eicosanoids

cell signaling molecules

arachidonic acid

20:4, precursor of eicosanoids

major FA components of phospholipids

linoleic and arachidonic acid

Very Low Density Lipoprotein (VLDL)

exports TAGs into circulation - PUFAS improve this export

what does VLDL production rely on?

C18:2 and C18:3 in liver

what species has reduced capacity to synthesize VLDL?

ruminants

beyond what carbon can animals not create C double bonds?

carbon-9

essential FAs

linoleic acid, oleic acid, a-linolenic

what FA is synthesized from linoleic acid?

arachidonic - activity of delta-6 desaturase is limiting

conditionally essential FA for cats

arachidonic

conditionally essential FA for cats and dogs

omega-3

enzyme that digests lipids in the small intestine

gastric lipase

digestive enzymes in exocrine pancreas

• pancreatic lipase

• co-lipase

• CEH

• phospholipase A2

pancreatic lipase

primary fat-digesting enzyme

co-lipase

anchors lipase to fat droplet

does the stomach remove one FA at a time?

yes

primary bile acids

colic acid, chenodeoxycholic acid

deoxycholic acid

dehydroxylized from chenodeoxycholic acid, secondary bile acid

conjugated bile acids in liver

taurocholic acid (taurine + cholesterol), glycocholic acid (glycine + cholesterol)

sequestrants

lower circulating cholesterol → prevents body from reusing bile acids

what percent of daily cholesterol synthesis is used for bile acid synthesis?

50%

chylomicrons

lipoproteins produced by small intestine; very high TAG and VLDL; largest of lipoproteins

LDL composition

low-density lipoprotein - half cholesterol

HDL

high density lipoprotein - half protein, dense

main precursor of milk fat synthesis

acetic acid