ch 11 Lipid and Amino Acid Metabolism Flashcards
emulsification
mixing of two normally immiscible liquids. Liquids that won’t normally mix
Dietary fat
consists mainly of triacylglycerols, but also has cholesterol, choleteryl esters, phospholipids and free fatty acids.
Digestion path
minimal in mouth and stomach; small intestines, emulsification which is aided by bile (containing bile salts, pigments and cholesterol and is secreted by the liver and stored in gallbladder). Then pancreas secretes pancreatic lipase, colipase, and cholesterol esterase into small intestines which hydrolyze lipid to 2-monoacylglycerol, free fatty acids, and cholesterol
micelles
formed to get absorbed in the small intestine (comprised of the free fatty acids, cholesterol and 2-monoacylglycerol) with water-soluble exterior and lipid interior
Absorption of lipids in digestion
micelles diffuse to brush border (of intestinal muscosal cells) and are absorbed. pass brush border, absorbed into mucosa and are packaged into chylomicrons (re-esterified to form triacylglycerols and cholesteryl esters and packaged with apoproteins, fat-soluble vitamins and other lipids). Chylomicrons leave intestine by lacteals (lymphatic vessels) and reenter bloodstream by thoracic duct which empties into the left subclavian vein at base of neck
hormone-sensitive lipase (HSL)
fall in insulin levels activates this. hydrolyzes triacylglycerols, yielding fatty acids and glcerol. Also activated by cortisol and epi
lipoprotein lipase (LPL)
necessary for metabolism of chylomicrons
albumin
carrier protein in blood transporting fatty acids
lipoproteins
transport triacylglycerol and cholesterol in the blood, made of apolipoproteins and lipids
chylomicrons
highly soluble in lymphatic fluid and blood; function to transport dietary tracyglycerols, cholesterol and cholesteryl esters to other tissues
VLDL (very low density lipoprotein)
produced and assembled in liver cells; main function - transport tracylglycerols to other tissues; contain fatty acids also
IDL (intermediate density lipoprotein)
VLDL remnant - what remains after triacyglycerol is removed from VLDL. Intermediate between chylomicrons and VLDL, and LDL and HDL, which transport cholesterol. This picks up cholesteryl esters from HDL to form LDL
LDL (low density lipoprotein)
deliver cholesterol to tissues for biosynthesis; plays important role in cell membranes and bile acids and salts in liver and steroidogenesis
HDL (high density lipoprotein)
cleans up excess cholesterol from blood vessels for excretion and delivers some cholesterol to steroidogenic tissues and transfers necessary apoliproteins to some of the other lipoproteins
apoliproteins
also called apoproteins; receptor molecules involved in signaling
de novo synthesis
form of synthesizing cholesterol other than LDL and HDL, occurs in liver and is driven by Acetyl-CoA and ATP
citrate shuttle
carries mitochondrial Acetyl-CoA into cytoplasm where synthesis can occur.
mevalonic acid
synthesis of this in the Smooth ER is rate limiting step of cholesterol biosynthesis
3-hydroxy-3-methylglutaryl (HMG) CoA reductase
enzyme that catalyzes rate limiting step of cholesterol biosynthesis
regulation of cholesterol synthesis
increased levels of cholesterol inhibit, insulin promotes, control of de novo synthesis depends on regulation of HGM-CoA reductase gene expression
specialized enzymes for transport of cholesterol
Lecithin-cholesterol acyltransferase (LCAT), and cholesteryl ester transfer protein (CETP)
fatty acids
long-chain carboxylic acids. Carboxyl is C-1 and C-2 is alpha carbon
Saturated fatty acids
no double bonds
unsaturated fatty acids
one or more double bonds
alpha-linolenic acid and linoleic acid
important essential fatty acids; poly-unsaturated, important in maintaining cell membrane fluidity
omega number system
used for unsaturated fatty acids; omega designates the position of the last double bond relative to the end of the chain and identifies the major precursor fatty acid; double bonds in natural fatty acids are generally cis
nontemplate synthesis
lipid and carb synthesis often referred to as this bc they don’t rely directly on coding of nucleic acid unlike protein and nucleic acid synthesis
Palmitic acid
also called palmitate - primary end product of fatty acid synthesis
acetyl-CoA carboxylase
rate-limiting enzyme for fatty acid biosynthesis; requires biotin and ATP; add CO2 to acetyl-CoA to form malonyl-CoA
fatty acid synthase
better name is palmitate synthase bc palmiate is the only fatty acid that humans can synthesize de novo; 8 acetyl-coA groups are required to produce palmitate (16:0); many of rxns performed by fatty acid synthase are reversed by beta-oxidation
triacylglycerol (triglyceride) synthesis
triacylglycerols are the storage form of fatty acids formed by attaching 3 fatty acids (as fatty acyl-CoA) to glycerol. formation occurs primarily in the liver and some in adipose.
beta-oxidation
how most fatty acid catabolism proceeds; takes place in mitochondria or in the peroxisome. Directly inhibited by insulin and stimulated by glucagon
alpha-oxidation
may occur in branch-chain fatty acids, depending on the branch points
omega-oxidation
happens in ER and produces dicarboxylic acids
pathway of beta-oxidation
fatty acids metabolized become activated by attachment to CoA which is catalyzed by fatty-acyl-CoA synthase produces fatty acyl-CoA. Then short (2-4 Cs) and medium (4-12 Cs) chain fatty acids diffuse freely into mitochondria while long (14-20 Cs) must use carnitine shuttle. Very long chains are oxidized elsewhere. in the mito, this processes reverses fatty acid synthesis, oxidizes and releases molecules of Acetyl-CoA, four step cycles each release one. and reduces NAD+ and FAD. NADH and FADH2 are oxidized in the ETC producing ATP. this process is used by liver to produce more acetyl-CoA
rate limiting enzyme of beta-oxidation
carnitine acyltransferase I
Four steps of beta-oxidation
- oxidation of fatty acid to form double bond; 2. Hydration of the double bond to form a hydroxyl group; 3. oxidation of hydroxyl group to form a carbonyl (beta-ketoacid); 4. splitting of the beta-ketoacid into a shorter acyl-CoA and acetyl-CoA
propionyl-CoA carboxylase
changes propionyl-CoA produced at end of beta oxidation by odd number carbon input to methylmalonyl-CoA which is then changed to succinyl-CoA by methylmalonyl-CoA mutase which requires B12 which is an intermediate in krebs or can be converted into malate for the gluconeogenic pathway
enoyl-CoA isomerase
monosaturated fatty acids, this changes the configuration from cis to trans for oxidative enzymes to act on fatty acids; between Cs 2 and 3; in polyunsaturated further reduction is required by 2,4-dienoyl-CoA reductase
steps in acetyl-CoA attachment to fatty acid chain
- attachment to acyl carrier protein, 2. bond formation bt molecules, 3. reduction of a carbonyl group, 4. dehydration, 5. reduction of a double bond
