Flashcards in Lecture 42 Deck (25)
What is the difference between synthase and synthetase?
Synthase - No ATP required to produce something
Synthetase - ATP required to produce something
Under what physiological conditions does Fatty Acid Oxidation (FAO) become predominant source of energy?
1) By heart muscle which almost exclusively depends on FA oxidation for energy
2) In diabetic patients in whom glucose metabolism is low
3) During periods of starvation
4) During periods of extended exercise (e.g. aerobics, running on a treadmill, running for long distances)
The major source of energy for this type of muscle comes from oxidation of fatty acids
By studying disorders of oxidation of fatty acids by mitochondria, scientists are now beginning to understand the following diseases:
1) Symptoms of Reyes-like syndrome
5) Developmental delay
6) In some cases sudden infant death syndrome (SIDS)
What is a description of the sequential steps in the oxidation of fatty acids?
1) Mobilization of fat from adipose tissue
2) Transport of fatty acids in plasma and their activation in the cells
3) Transport of activated fatty acids to mitochondria and oxidation
4) Formation of and utilization of ketone bodies (excess FA oxidation in starvation and diabetes)
5) Regulation of fatty acid oxidation
Which hormones affect lipolysis?
Lipolysis inducing hormones:
Lipolysis inhibiting hormone:
How does albumin work in lipolysis?
Serum albumin acts as a free fatty acid carrier in the blood
What are the steps during mobilization of fatty acids in lipolysis?
1) Lipolysis by hormone activation
2) Adenylate cyclase converts ATP to cAMP
3) Protein kinase is then activated to phosphorylate (and activate) triacylglycerol lipase
4) triacylglycerols are then converted to free fatty acids and glycerol
5) fatty acids and glycerol are released from the cell and into the blood stream
What occurs to fatty acids when they are transported from the plasma to a cell?
They are bound to Fatty Acid Binding Protein (FABP) in the cytoplasm
What happens to fatty acids once they have bound to Fatty Acid Binding Protein (FABP) in the cytoplasm?
1) Fatty acids travel to the outer mitochondrial membrane
2) Acyl CoA synthetase in the outer mitochondrial membrane combines Fatty acids to CoA using ATP to form Acyl CoA
(Fatty Acid + CoA + ATP --> AMP + Pi + Acyl CoA)
3) Acyl CoA then crosses into the mitochondrial intermembrane space (cannot go through inner mitochondrial membrane by itself)
What happens to Acyl CoA once it is in the intermembrane space of the mitochondria?
1) Acyl CoA + Carnitine --> Acyl-carnitine with the use of Carnitine acyltransferase 1 in the outer mitochondrial membrane
2) Acyl-carnitine passes through the inner mitochondrial membrane and into the mitochondrial matrix with the help of Carnitine/acylcarnitine translocase
3) Acyl-carnitine + CoA --> Acyl-CoA + carnitine with the help of carnitine acyltransferase 2
4) Acyl-CoA can now be used for fatty acid oxidation (Beta-oxidation) in the mitochondrial matrix
What are the steps of the beta-oxidation pathway?
1) Long Chain Acyl-CoA dehydrogenase (LCAD), Medium Chain Acyl-CoA dehydrogenase (MCAD), & Short Chain Acyl-CoA dehydrogenase (SCAD) are used to convert Acyl CoA to 2-trans-enoyl CoA (FAD is reduced in the process to FADH2)
2) 2-trans-enoyl CoA --> L-3-hydroxy acyl CoA; uses H2O & Enoyl CoA hydratase is the enzyme
3) L-3-hydroxy acyl CoA --> 3-ketoacyl CoA; reduces NAD+ to NADH & 3-Hydroxy acyl CoA dehydrogenase is the enzyme
4) 3-ketoacyl CoA + SCoA --> Acetyl CoA; 3-ketoacyl CoA thiolase is the enzyme
What is common in SIDS patients (in kids, in particular) who have died from fatty acid oxidation deficiency?
Major causes are due to a deficiency in Medium Chain Acyl CoA Dehydrogenase (MCAD)
How do you know how many cycles it will take to oxidize a fatty acid?
(The # of Carbons - 2) / 2
(e.g. Palmitoleic Acid = 16C, 7 cycles)
The oxidation of a ______ fatty acid produces more energy than the oxidation of a _____ fatty acid
saturated; unsaturated (for every double bond, you will not reduce FAD to FADH2 because you bypass the double bond)
What is different about plant and animal fatty acids?
1) Plants have an odd number of carbons in their fatty acid chains, resulting in a slightly different beta oxidation process
2) Instead of just producing Acetyl CoA from oxidation, plant fatty acid oxidation also results in the production of a Propionyl CoA
3) Propionyl CoA can be converted to Succinyl CoA to be used in the citric acid cycle
How does the body produce energy in times of starvation or diabetes?
1) Excessive Fatty Acid oxidation in mitochondria
2) Ketone body formation through the use of Acetyl CoA produced from fatty acid oxidation
Describe the steps of ketone body formation
1) 2 Acetyl CoA --> Acetoacetyl-CoA with the use of Beta-ketothiolase
2) Acetoacetyl-CoA --> 3-hydroxy-3-methyl Glutaryl-CoA (HMG CoA) with the use of Acetyl CoA
3) HMG CoA --> Acetoacetate with the use of HMG CoA lyase
4) a) Acetoacetate --> Acetone + CO2
b) Acetoacetate --> D-3-hydroxybutyrate witth the use of D-3-OH butyrate dehydrogenase and the reudction of NAD+ to NADH
What happens to the plasma concentration of ketone bodies, glucose, free fatty acids, & acetoacetate during starvation?
As blood glucose levels decrease, the levels of ketone bodies, free fatty acids, & acetoacetate all increase in the blood
How are ketone bodies utilized?
They can be used by the heart, brain and muscle for energy
Describe the process of ketone body breakdown
1) D-3-hydroxybutyrate is broken down into acetoacetate by 3-hydroxybutyrate dehydrogenase
2) Acetoacetate is broken down into acetacetyl CoA by Succinyl CoA:Acetoacetate CoA Transferase and produces Succinate from Succinyl CoA in the process
3) Acetoacetyl CoA is broken down into 2 Acetyl CoA by thiolase
Is the concentration of ketone bodies in the blood ever zero, even if one is full from eating?
Absolutely not. There are always ketone bodies in the blood
How is fatty acid oxidation (FAO) regulated?
1) Enzyme CPTI (carnitine-palmitoyl transferase 1) is the rate limiting enzyme. It is inhibited by Malonyl CoA, a product formed during fatty acid synthesis
2) Hormonal regulation of FA oxidation:
a) Glucagon increases triacyl glycerol or hormone sensitive lipase (more breakdown)
b) Epinephrine increases triacyl glycerol or hormone sensitive lipase (more breakdown)
c) Insulin decreases triacyl glycerol or hormone sensitive lipase (less breakdown)
What are four types of FAO deficiencies?
1) Carnitine deficiency - corrected by adding cartinitine to diet
2) Fattyacyl CoA synthetase deficiency - give patient C8-C10 fatty acids because they get into the mitochondrial matrix just as easily as free fatty acids
3) Short chain (SCAD - C4, C6, C8), medium chain (MCAD - C8, C10, C12), long chain (LCAD) & multi-chain (MCAD) dehydrogenase mutations - required test for neonates (cannot transport carnitine into mitochondrial matrix)
4) Acyl Carnitine-Carnitine translocase mutations