What is an anaplerotic reaction?
Reaction to replenish intermediates of an metabolic pathway (such as the citric acid cycle) as they are removed to serve as biosynthetic precursors
A eaction to replenish intermediates of an metabolic pathway (such as the citric acid cycle) as they are removed to serve as biosynthetic precursors is a(n) ________________ reaction
What are four important roles of fatty acids?
-building blocks of phospholipds and glycolipds
-hydrophobic modifiers of proteins (membrane targeting)
-hormones and intracellular messengers
Fatty acids are stored in ______ tissue as ____________
adipose tissue as triacylglycerols
Fat cells are called ___________
Vertebrates (can/can not) make fatty acids from sugars.
Triacylglycerols can be mobilized by the hydrolytic action of hormone-controlled __________
Glucagon and epinephrine (stimulate/inhibit) triacylglycerol breakdown.
Glucogon and epinephrine (activte/inhibit) lipase activity
Activation of lipase by glucagon or epinephrine occurs via what mechanism?
phosphorylation cascade (signal transduction)
Hydrolized triacylglycerols are converted into _________ and __________
fatty acids and glycerol
How are fatty acids transported after leaving the adipocyte?
-bound by serum albumin in blood
-carried as a complex
-enter nonadipose tissue cells (such as muscle cells or myocytes) after release from serum albumin via a specific fatty acid transporter
Fatty acids are carried in the blood bound by ______________
Fatty acids carried in the blood by serum albumin are released by a specific _____________
fatty acid transporter (i.e. membrane bound in myocyte)
Fatty acids are (oxidized/reduced) in nonadipose tissue cells
How is glycerol transported in the blood after leaving the adipocyte?
absorbed and further processed by liver cells
Phosphorylation of ____________ in the adipocyte allows for destabilization of the lipid droplet so lipase may function
What transports fatty acids from storage cells to tissue cells?
What two fates does glycerol have upon entering liver cells?
-pyruvate via glycolysis
-glucose via gluconeogenesis
How is glycerol altered so it may enter either glycolysis or gluconeogenesis?
1. phosphorylation by glycerol kinase to yield glycerol 3-phosphate
2. oxidation by glycerol phosphate dehydrogenase to yield dihydroxyacetone phosphate (an isomer of glyceraldehyde 3-phosphate)
Saturated fatty acids are activated to ______ on the cytosolic side of the mitochondrial outer membrane
Where are saturated fatty acids activated to acyl-Coa?
cytosolic side of the mitochondrial outer membrane
short-chain acyl-Coa (10 or fewer carbons) enter mitochondria via ___________
How do long-chain acyl-CoA (12-18 carbons) enter the mitochondrial membrane?
carnitine shuttle system
Where does the oxidation of acyl-CoA to acetyl-CoA occur?
mitochondrial matrix (occurs via beta-oxidation)
Acyl-CoA is (oxidized/reduced) to acetyl-CoA in the mitochondrial membranes
oxidized (via bet-oxidation)
How are fatty acids activated to acyl-CoA?
-fatty acid carboxylate ion is adenylated by fatty acyl-CoA synthase with the addition of ATP (yields acyl adenylate + PPi)
-acyl adenylate is attacked by the thiol group od coenzyme A, displacing AMP and forming thioester fatty acid-CoA (acyl-CoA)
What is the carnitine shuttle system?
long-chain fatty acids are transferred to carinitine by carnitine acyltransferase I, transported (as acyl carnitine) via a carnitine transporter, and released from carnitine in the mitochondrial membrane by carnitine acyltransferasea II
What is beta-oxidation?
series of reactions that cleaves two carbon atoms at a time from the carboxyl end of a fatty acid
One complete cycle of beta-oxidation requires _____ catalyzed reactions
What is the first step of beta-oxidation?
Dehydrogenation by FAD: The first step is the oxidation of the fatty acid by Acyl-CoA-Dehydrogenase. FADH2 + trans-Δ2-enoyl-CoA is produced
What is the second step of beta-oxidation?
Hydration: The next step is the hydration of the bond between C-2 and C-3 by enoyl-CoA hydratase and with the addition of H2O. L-β-hydroxyacyl CoA is produced
How many isoenzymes of mitochondrial acyl-CoA-dehydrogenase exist, and what are their purposes?
-very-long chain AD for fatty acids 12-18 C long
-medium chain AD (4-14 C)
-short chain AD (4-8 C)
What is the ultimate fate of electrons removed from fatty acyl-CoA?
first transferred to FAD, then eventually to ubiquinone as part of the respiratory electron transport chain
What is the third step in beta-oxidation?
Oxidation by NAD+: The third step is the oxidation of L-β-hydroxyacyl CoA by NAD+ by β-hydroxyacyl CoA dehydrogenase. This converts the hydroxyl group into a keto group and the NAD+ into NADH. β-ketoacyl CoA is produced.
What is the fourth step of beta-oxidation?
Thiolysis: The final step is the cleavage of β-ketoacyl CoA by the thiol group of another molecule of CoA. The thiol is inserted between C-2 and C-3, yielding an acetyl CoA molecule, and an acyl CoA molecule that is two carbons shorter. Enzyme: thiolase
Each round of beta-oxidation produces one _________
What are the three stages of mitochondrial oxidation of fatty acids?
Stage 1: beta oxidation produces acetyl-CoA and NADH/FADH2
Stage 2: acetyl CoA ebters the citric acid cycle, producing electrons
Stage 3: NADH/FADH2 from Stage 1 and electrons from Stage 2 enter the electron transfer chain to yield ATP
One additional reaction (isomerase) is required for the oxidation of _________ fatty acids
What additional reactions are needed for the oxidation of polyunsaturated fatty acids?
The last cycle of an odd-numbered fatty acid undergoing beta-oxidation yields a ____________
propionyl-CoA (which is also an intermediate in catabolic pathways of amino acids)
What happens to propionyl-CoA?
1. carboxylation by propionyl-CoA carboxylase to yield D-methylmalonyl-CoA. Biotin is required as a cofactor
2. D-methylmalonyl-CoA is converted to L-Methylmalonyl-CoA by nethylmalonyl-CoA epimerase
3. L-Methylmalonyl-CoA is converted to succinyl-Coa by methylmalonyl-CoA mutase. Cobalamin is required as a cofactor
Biotin is dependent on ____ and mediates ___________ reactions
B-12 is an important cofactor in the transfer of _______ groups
Methylmalonyl-CoA mutase requires __________ as a cofactor
What molecule is formed as methylmalonyl-CoA mutase rearranges L-Methylmalonyl-CoA ?
In animals, what do peroxisomes specialize in?
oxidation of very-long-chain fatty acids (20 or more C) and branch fatty acids
How does oxidation of fatty acids differ in peroxisomes and mitochondria?
-in peroxisomes, electrons from the first oxidation step are directly transferred to O2, generating H2O2 (catalase converts H2O2 to H2O and 1/2 O2)
-peroxisomes lack an electron transport chain
-acetyl-CoA is exported (citric acid cycle does not occur in peroxisomes)