dietary lipids

what are fatty acids?
long chain hydrocarbons with a carboxyl group on one end
how do fatty acids differ?
they differ in the degree of saturation and the number of carbons
what does the degree of saturation in fatty acids refer to?
the presence or absence of C=C bonds in the hydrocarbon region. fatty acids with = bonds are considered unsaturated, while fatty acids with – bonds are considered saturated
what are the 3 ways of numbering carbons in fatty acids?
1)start w/the carboxyl carbon and count down
2) start w/the carbon after the carboxyl carbon and go down the greek alphabet
3) start with the last carbon farthest from the carboxyl group and count toward the carboxyl as such: omega1, omega2, omega3 fatty acid…etc
what shape does a C=C bond give? is it saturated or unsaturated?
C=C will give a bend, (due to its cis form), it is unsaturated, (carbon is not saturated with H)
what shape does a C-C bond give? is it saturated or unsaturated?
C-C bonds give a linear shape. they are saturated, (saturated with more H’s)
what form do saturated fatty acids take at room temperature? what foods have them in high amounts?
saturated fats take solid forms at room temperature b/c they stack well. dairy, meat fat, and coconut/palm oil are examples
what form do mono- and polyunsaturated fats take at room temperature? what foods have them in high amounts?
mono- and polyunsaturated fats are liquid at room temperature. they are also found in meat, nuts, and plant oils, (canola, olive)
what are the # of carbons for short chain, medium chain, long chain, and very long chain?
SCFA:2-3, MCFA:4-11, LCFA: 12-20, VLCFA: 20+
what is the typical fatty acid found in biological systems?
usually even number of C’s between 14-24, w/16 and 18 being most common. most unsaturated FAs have cis
how does chain length affect the melting point of a fatty acid?
the longer the chain length, the higher the melting point
how does the degree of unsaturation affect the melting point?
the more unsaturation, (the more C=C bonds), the lower the melting point
what generally happens to the fatty acids produced in the body?
they are made into CoA derivatives
what are the 2 essential fatty acids? why are they essential? what omega acids do you get from them?
linoleic and linolenic. we don’t have the enzyme to add double bonds to carbon 12 or 15, (basically anything past 9). omega 6 from linoleic and omega 3 from linolenic.
what is the precursor for linoleic acid? what is that amino acid an important precursor for?
arachidonic, which is a precursor for compounds that regulate processes including blood clotting and blood pressure
where do you find the precursor for omega 6?
linoleic acid is found in safflower/soy/corn oil
where do you find the precursor for omega 3?
linolenic acid is found in fish/walnut/flaxseed/green leafy vegetables
which fatty acid is ultimately pro-inflammatory? which has the opposite effect?
omega 6 is ultimately pro-inflammatory, omega 3 counteracts this
are triglycerides and triacylglycerols the same thing?
yes
what does is a triglyceride composed of?
3C glycerol backbone and 3 fatty acids
is glycerol a charged molecule? are fatty acids polar? what about triglycerides?
yes, glycerol and fatty acids have -OH groups. trigylerides are very non-polar
what is one thing that affects membrane fluidity?
level of unsaturated fatty acids, the more there are, the more fluid a membrane will be to allow transmembrane proteins to function correctly
why are bent unsaturated bonds easier to break than trans unsaturated? what do trans unsaturated fats resemble?
bent b/c they are cis, which are easier to break than trans bonds, (TRANSFATS -> resemble saturated fats)
what is the most health of these 3: butter, vegetable oil, margarine?
vegetable oil, butter, margarine
why is vegetable oil more healthy than butter?
vegetable oil has less saturated fats than butter, (58%-20%0, and vegetable oil has less trans fats than butter, (~3% – 0%)
why is butter more healthy than margarine?
butter has more saturated fats than margarine, (58%-20%), but margarine has more trans fats than butter, (~40%-~3%).
why is there 40% trans fat in margarine?
margarine is hydrogenated vegetable oil, so that it can be made into cakes etc, and half of vegetable oil’s 80% unsaturated fat is made into trans in the process of maragine creation
what 2 main groups do lipids break down to?
non-polar storage lipids and polar membrane lipids, (amphipathic)
what is the most important use for lipids in the cell?
membrane formation
what is monoacylglycerol, why is it often written 2MG?
monoacylglycerol has one fatty acid on carbon 2, and an alcohol on the 1st and 3rd carbon, (giving some polarity)
what are phospholipids used for? what do they consist of?
cell membrane construction and fat transport in the bloodstream. they consist of a glycerol backbone, 2 fatty acids, and a phosphate with a head group, (often alcohol, something polar)
what phospholipid is involved in acute respiratory distress syndrome?
phosphatidyl choline
what is ceramide?
sphingosine and a fatty acid w/one open spot
what is sphingomyelin? what kind of sphingolipid is it? why is it special?
ceramide and a phosphate+choline, sphingophospholipid -> primary sphingolipid in humans
what is galactocerebroside? what kind of sphingolipid is it?
ceramide+galactose, glycosphingolipid
where are sphingolipids found? what is a cerebroside?
they are a major part of the nervous system, and also biological membranes. a cerebroside is a glycosphingolipid that is important in the muscle and nerve membrane
what kind of fatty acids are important for sphingolipids?
long chain fatty acids, (mothers milk for infants rather than cows)
what is cholesterol made from?
acetyl CoA
what are important uses of cholesterol?
cell membrane structure, (particularly nerves), participation in metabolic pathways, sterols -> sex, adrenal hormones, bile acids, and Vit D
is cholesterol polar?
cholesterol has a hydroxyl group that allows it to interact with water, but a fatty acid can be added here to creata a nonpolar ester
cholesterol is a precursor to bile which has what properties that make it a good detergent?
one very polar side and one non polar side, allows it to protect lipids from getting mixed water
what are the 4 lipid soluble vitamins?
D,(calciferol), E, (alpha tocopherol), K A, (retinol)
what kind of vitamins are easier to get toxicity?
lipid soluble, harder to get rid of faster
what is the first thing that happens in lipid, (triglyceride), digestion?
emulsification by bile salts, produced in the liver, delivered via the gall bladder and secreted into the intestinal lumen
what are the 2 important functions of bile salts?
bile salts 1)emulsify lipids for digestion and 2)make the products of lipid digestion soluble
how are bile acids regulated?
the first step is product inhibited
what are the 2 bile acids produced in the liver?
cholic acid and chenocholic acid
what is the next step after bile acids are made? where does this happen
conjugation with either glycine or taurine in the liver to increase solubility
how do bile salts interact/emulsify with lipids?
the bile salts surround the lipid molecule with the noncharged side facing in and the polar side facing out
how much bile acid is produced per day/excreted per day? how much is there total?
.8 g is made and excreted every day. there is a total pool of ~3-5g bile acid in the body
how much bile acid is recycled/excrected daily?
95% recycled/5% excreted
how is bile recycled?
most bile salt is actively transported into the portal vein back to the liver from the intestine. a small amount is deconjugated by the bacteria and brought back via passive transport
how is the liver involved in lipid digestion?
the liver produces bile salts and sends them to the gall bladder
how is the pancreas involved in the digestion of lipids?
it secretes the lipases which digest fat, the main one for dietary fat is pancreatic lipase and its enzyme, colipase. bicarb is also made to buffer the acids/enzymes
how are the mouth and stomach involved in lipid digestion?
lingual and gastric lipase are used to digest short and medium chain fatty acids
how is the intestine involved in the digestion of lipids?
the intestine is where micelles are created, which are smaller fat droplets with a better surface area for catabolism
what role does gastric lipase play in lipid digestion?
gastric lipase digests triglycerides with SCFA and MCFAs in the larger emulisified lipid aggregations, releasing the SCFA and MCFAs as well as diacylglycerols and monacylglycerols
what do the free SCFA and MCFAs do once gastric lipase
free SCFA and MCFAs are carried to hepatic portal blood from the intestine and carried by albumin to the liver
what happens to LCFAs after SCFA and MCFAs are digested?
pancreatic lipase and colipase along with more bile salts form micelles which can then be absorbed across the intestinal epithelium
how does pancreatic lipase cut triglycerides?
pancreatic lipase cuts the ester bonds of the 1st and 3rd FA of a TG, giving monacylglycerol and 2 FAs as products
what is the action of colipase?
the outer surface of the emulsified fat inhibits lipase, so colipase binds to it and then lipase can bind to that in order to perform its function. (colipase is secreted as a zymogen)
how does orilstat work?
inhibits pancreatic and gastric lipase -> fat just goes right through
what does cholesterol esterase do?
cholesterol esterase removes the ester bond between a cholesterol and a FA, thereby making cholesterol polar again and absorbable
what breaks down phospholipids such as phosphatidylcholine?
phospholipase, which cuts off and FAs and leaves phosphate groups. it is secreted as a zymogen and its activity is increased in the prescence of bile salts
how do micelles form?
the digestive enzymes on the oil/water surface of large emulsified lipid droplets begin to crowd, pinching off little droplets -> micelles
what do micelles contain? where do they go?
free FA, lyso-phospholipids, 2-MG, cholesterol, fat-soluble vitamins, and small amounts of bile salts. they move to the border of the intestinal mucosal cells where the lipids are absorbed.
what are the 2 regulatory hormones of lipid digestion?
cholecystokinin and secretin
what is the action of cholecystokinin?
cholecystokinin is secreted by cells in the mucosa of the jejunum and lower duodenum, and it acts on the gall bladder/exocrine portion of the pancreas to release bile salts and digestive hormone respectively. cholecystokinin also decreases stomach motility, slowing the entrance of lipids into the small intestine
what is the action of secretin?
secretin causes the pancreas to release bicarbonate to neutralize the pH of the intestine
what happens to the contents of micelles when they enter epithelial cells?
the trigylcerides, cholesterol esters, any previous lipid structures that had been broken down in the intestine are reformed, and grouped into chylomicrons
where do chylomicrons enter?
the lymphatic system, then the blood
do SCFA and MCFAs require bile salts for absorption? do they need to be packaged?
SCFA and MCFAs do not need bile salts for absorbtion or do they need to be packaged for distribution
what are chylomicrons mainly composed of? what is their structure?
85% triglycerides. they are a lipid droplet surrounded by more polar lipids then a layer of proteins
how are chylomicrons formed?
micelles are brought into the intestinal lumen cell, the proteins are processed in the RER, the fats are processed in the SER and both are sent to the golgi complex where the lipoprotein is formed
when chylomicrons are released into the blood, what changes occur.
chylomicrons already have ApoB, but they aquire Apo-C and Apo-E from HDL
where do chylomicrons go once they have all their surface proteins?
chylomicrons circulate the blood until they get to lipoprotein lipase which responds to the Apo-C protein and catabolize the chylomicrons
what regulates lipoprotein lipase?
insulin raises levels of LPL, (problem with diabetes)
what does lipoprotein lipase do to the contents of chylomicrons?
the triglycerides are broken down into free fatty acids and glycerol, (which is converted to glycolytic intermediate DHAP)
what tisses can oxidize fatty acids?
heart and skeletal muscle, liver, kidney
what tissues cannot oxidize fatty acids?
brain, RBCs, adipose
lipoprotein lipase is synthesized mainly by which tissues?
endothelial cells of capillary walls in muscle and adipose tissue
what happens to the remnants of chylomicrons?
they are taken up by receptor-mediated endocytosis, in the liver where lysosomal enzymes digest the remnants, releasing them for use by the liver
what happens to fatty acids released by lipoprotien lipase?
they are oxidized by the cells that need them or stored as triglycerides
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