3/4/23 - Lipids

Lipids

Generally insoluble in water, important source of energy, essential for cell membranes, hormone synthesis, and fat-soluble vitamin absorption.

Fatty acids

Straight chain hydrocarbons with a carboxyl group, building blocks of complex lipids, can be saturated (SFA) or unsaturated (UFA).

Double bonds

Influence membrane fluidity and energy content, more double bonds mean less energy and lower melting point.

Triacylglycerol (TAG)

Storage form of lipids, composed of glycerol and three fatty acids, broken down by lipases.

Phospholipids

Important for cell membranes, microbial phospholipids are digested in the small intestine.

Emulsification

Increases lipid droplet surface area, involves physical (chewing) and chemical (bile) processes.

Pancreatic lipase

enzyme secreted by the pancreas and works in the small intestine. This enzyme hydrolyzes fatty acids from the Sn1 and Sn3 positions, turning TAG into DAG and an FFA, and turning DAG into MAG and an FFA. Requires colipase for optimal activity, because colipase creates a binding site for pancreatic lipase on a fat droplet.

Microbial lipid utilization

1) hydrolysis of glycerol and FAs, 2) hydrogenation/biohydrogenation of UFAs, and 3) microbial phospholipid synthesis.

Hydrolysis of the glycerol and FAs (microbial digestion)

glycerol + sugar are fermented by the microbes into VFAs

TAG, glycolipid, phospholipid, processed by lipase, galactolipase, phospholipase, and turned into glycerol, FFAs, sugar (glycolipid), and polar head group (phospholipid)

rapid and complete

hydrogenation (microbial digestion)

slow and incomplete

turns UFAs into SFA using hydrogenase to add hydrogens

MPL synthesis

increased microbial growth —> increased MPL synthesis

Chylomicron

Contains B-48 and TAG, transports lipids after absorption in the small intestine.

Saturated Fatty Acids

contain no C=C double bonds, contain all of the hydrogens they can

Unsaturated fatty acids

contain one or more cis C=C double bonds, each double bond is missing two hydrogens, can be MUFA or PUFA, act as a hydrogen sink (accepts H2), are toxic to cellulolytic ruminal microbes

Monounsaturated fatty acids

contain 1 C=C double bond

Polyunsaturated fatty acids

contain > 1 C=C double bond

Non ruminant lipid digestion

TAG —> (hydrolyzed by lipase) —> (release FFA) —> DAG —> (hydrolyzed by lipase) —> (release FFA) —> MAG

shared characteristics of Ligual Lipase and Gastric Lipase

produced continuously, production increases with increased fat or lipid intake, stable and active at the low pH of the stomach, both act on fatty acids at the Sn3 position, prefer short chain FAs, important in newborns

physical emulsification

mixing that occurs in the stomach and as food enters the small intestine, chewing

chemical emulsification

bile, lysolecithin

what does bile do

mixed with digesta in the duodenum, stabilize the fat droplet, stored in the gallbladder (except in the horse), synthesized from cholesterol in the liver

lysolecithin

desorbs SFAs from feed particles

small intestine

primary site of lipid digestion and absorption, stabilized fat droplets (bc of bile), emulsification and enzymatic digestion with pancreatic lipase and colipase

Mouth

minimal digestion, lingual lipase

stomach

more digestion (TAG and small amount of DAG and FFA)

large intestine/cecum

undigested lipids are acted on by microbes and MPL is synthesized

Lingual Lipase

enzyme produced by the salivary glands. This enzyme is used in the mouth and stomach to break down TAG at the Sn3 bond, using hydrolysis to turn TAG into DAG and FFAs.

gastric lipase

enzyme produced by the chief cells in the stomach. It is used in the stomach to hydrolyze the Sn3 bonds of TAG to produce DAG and FFAs.

Procolipase

protein produced by the pancreas. Is the inactive form of colipase, which is used to assist pancreatic lipase. Is activated in the small intestine by trypsin, changing it into colipase.

Lipase (ruminal)

enzyme used to break down fatty acid chains (TAG) in the rumen and large intestine. Each one differs in what position they attack the TAG, but all of them do so by inserting a water molecule (hydrolysis).

galactolipase

enzyme found in the microbes of fermentation chambers (rumen and large intestine). Is used to break down glycolipids into glycerol, 2 FFAs, and a sugar.

phospholipase

enzyme found in the microbes of fermentation chambers.  It is used to break down phospholipids into glycerol, 2 FFAs, and a polar head group.

hydrogenase

enzyme found in the microbes in fermentation chambers. Changes UFAs into SFAs by inserting one or multiple hydrogens in the UFA. 

Diacylglycerol (DAG)

another form of lipid storage. Is formed when one of the fatty acid tails is cleaved from a TAG. Can be further broken down into MAG and FFAs for energy use.

Monoacylglycerol (MAG)

Is the the final stage of TAG breakdown. Is made of a glycerol backbone and only one fatty acid tail. Can be directly absorbed in the small intestine to be used for energy.

free fatty acid (FFA)

are the result of TAG breakdown. Are absorbed in the small intestine of the animal to be used for energy.molecul

molecules that contain an ester bond or can form an ester bond

Acyl CoA synthetase, TAG, DAG, MAG

proteins secreted by a mammal digesting lipids

lingual lipase, gastric lipase, pancreatic lipase, procolipase

molecules that hydrolyze an ester bond at the Sn3 position

lingual lipase, gastric lipase, pancreatic lipase, lipase (microbial), galactolipase

molecules that hydrolyze an ester bond at the Sn1 position

pancreatic lipase, lipase (microbial), phospholipase

molecules that hydrolyze an ester bond at the Sn2 position

lipase (microbial), galactolipase, phospholipase

ruminal utilization of lipids results in a decrease in the amount of ____ absorbed in the small intestine

MAG, PUFA, MUFA

who forms the most microbial phospholipid in the large intestine/cecum?

horse

to increase microbial phospholipid synthesis in calves eating forage, what two polysaccharides would be best to feed?

amylose, amylopectin

who absorbs the most MPL in the large intestine?

cow = horse = pig

energy from VFAs ranking

cow >horse > pig

MPL synthesis ranking

cow > horse > pig

lysolecithin usage ranking

cow > horse = pig

Procolipase/colipase usage ranking

pig > horse > cow

SFA production ranking

Cow > horse > pig

pancreatic lipase function without colipase

cow = horse = pig

lipid breakdown in fermentation chamber

cow > horse > pig

fat hardness ranking

cow > horse > pig