Lipids: Biosynthesis of Fatty Acids Flashcards
HCl
secreted by parietal cells to help digest protein in stomach.
Chief cells
secrete pepsinogen, which is activated by HCl to pepsin. Breaks down protein to peptides
Trypsinogen
in the intestines, converts to trypsin which is the active form by enteropeptidase.
trypsin
activates trypsinogen, chymotrypsinogen, proelastase, and procarboxypeptidase A and B. Peptides break down into tri and di and amino acids
Intestinal lumen
absorbs di and tri peptides and amino acids through Na+ dependent secondary active transport
a-amylase
secreted by salivary when starch, lactose, or sucrose enter the mouth
HCl from cheif cells
stop the salivry amylase
Pancreas
secretes a-amylase to help break down the carbs that go into the intestines and tri and oligosaccharides, maltose and isomaltose
Carbs absorbed
ONLY monosaccharides, these are transported from the cell to the blood by facilitated diffusion
Glucose, fructose and galactose
used by cell for energy
stored as glycogen
enter portal circulation and go to the liver to be converted to fat.
Duodenum
where most fat digestion occurs.
Fat globule
bound by bile salts from the liver and a phospholipid which causes emulsification. This increases the surface area of the hydrophobic lipid.
Jejunum
free fatty acids, cholesterol, and 2-monoacylglycerol are primary products of dietary lipid degradation here. They mix with bile salts to form micelles.
Micelles
disk shaped clusters of amphipathic lipids. Mixed micelles are soluble in aqueous solution of the intestinal lumen. Their hydrophilic suface helps facilitate transport of hydrophic lipids
Enterocytes
primary site of particle absorption at the brush border membrane
Which FA are directly absorbed into bloodstream?
short and medium chain. Do not require mixed micelles. This makes them an effective way to give people energy
mono and diacylglycerolacyltransferase
converts 2-monoacylglycerols to triacylglycerols. occurs within the cell
Chylomicrons
Triacylglycerols and cholesteryl esters and incorporated into them. released by exocytosis from enterocytes into the lacteals. They travel through lymph, enter blood. Go to peripherals.
Lacteals
lymphatic vessels. Basically the immune system and waste disposal
Fatty Acids
low levels are in all tissues. Found in fatty acyl esters in more complex molecules. 90% contained in lipoprotein particles. HDL and LDL. Large amounts in plasma during fasting Transported in blood by albumin Precursors to hormones Stored in adipose Major energy reserve
Structure of FA
Hydrophobic hydrocarbon chain
terminal carboxyl group - high water affinity, amphipathic (hydrophobic compound with a hydrophilic end)
Long chain FA hydrophobic portions predominate
Saturated FA
No double bonds
longer FA, higher meling point
solid at room temp
butter
Unsaturated FA
Double bonds - create a kink Lower melting point Cis config - Trans is synthetic Liquid at room temp Oil They produce less energy, are less highly reduce, and less products are produced
Cis config
loose pliable membranes,
Trans config
still membranes –> CV disease
hydrogen gas is pushed through an unsaturated FA. Converts to saturated. Some double bonds reform, but it is different
Linoleic acid (w-6)
can metabolize into arachidonic acid
Key part in Dihomogamma linolenic acid
potentially produces PGE1 prostaglandins non-inflamatory
anti-spasmotic
can potentially product PGE2 - inflammatory prostaglandins
Linolenic acid (w-3)
Metabolized into PGE3 - non inflammatory
inhibits AA production
deficiency results in decreased vision and altered behavior.
VLDL
assembled in liver from cholesterol and apolipoproteins.
Convertd to LDL in bloodstream
Transport endogenous products (chylomicrons exogenous)
associated with small dense LDL and TG - marker of metabolic syndrome, particularily atherogenic
De Novo Synthesis of FA
supplied by diet as carbs, proteins and other molecules in excess
Stored as triacylglycerols
Synthesis occurs primarily in the liver and lactating mammary glands - some in adipose
uses Acetyl CoA from glycolysis and kreb cycle
Fatty Acid Synthase
mnomer is multicatalystic polypeptide with seven different enzymatic activities plus domain
Domain covalently binds to 4’phosphopanteheine - is a derivative of pantothenic acid and an enzyme component of vitamin A
Storage
mono, di, and tri cylglycerols consist of one, two, or three molecules of faty acid esterified to a molecule of glycerol.
Triacylglycerol structure
3 FA esterified to a glycerol molecule. Not typically same
C1 FA saturated
C2 FA unsaturated - decrease melting temp
C3 FA either
Glycerol Phosphate
initial acceptor of FA during TAG synthesis
made in liver and adipose. Adipocytes can take up glucose only in presence of insulin. Low plasma glucose and insulin limit capacity to synthesize glycerol phosphate.
2 pathways - 1st from glucose using reactions from glycolysis produced by dihyroxyacetone phosphate
Reduced by glycerol phosphate dehydrogenase
2nd only in lvier uses glycerol kinase
FA to active form
must be converted to active form (have a CoA attached) before it can TAG synthesis
Fates of TAG
Adipose - stored in cytosol of cells. anyhydrous
“Depot Fat” - available to mobilize when fuels needed
Liver - very little
exported, packaged with cholesteryl esters, cholesterol, phospholipid and protein to form lipoprotein particles VLDL
VLDL secreted into blood
Mature and function to deliver endogenously derived lipids to peripheral tissues
Release FA from TAG
mobilization requires hydrolytic release of FA and glycerol
Initiated by hormone sensitive lipase - which removes FA from C1 and or C3
Additional lipases specific for di and mono acylglycerols remove the remaining FA
Glycerol
released during TAG degradation.
Cannot be metabolized by adipocytes
lacks glycerol kinase
Transported to liver - phosphorylated - used to form TAG in liver or converted to DHAP
Hormone-Sensitive Lipase
activated by phosphorylated by 3’ 5’ cyclic AMP dependent protein kinase. Produced in adipocyte. Binds to receptors on the cell membrane. Activated adenylate cyclase.
