Download - 907471 properties-of-triacylglycerols
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Properties of Triacylglycerols
1. Hydrolysis• triacylglycerols undergo stepwise enzymatic
hydrolysis to finally liberate free FA and glycerols
• catalyzed by lipases• important for digestion of fat in the GIT and fat
mobilization from the adipose tissues
2. Saponification• hydrolysis by alkali to produce glycerol and
soaps
Triacylglycerol + 3 NaOH Glycerol + 3R-CooNa (soaps)
3. Rancidity• term used to represent the deterioration of fats
and oils resulting in an unpleasant taste• fats with UFA - more susceptible • occurs when fats are exposed to air, moisture,
light and bacteria
Metabolism of Lipids
Cholesterol, the most feared among the lipids, speaks:
“Consumed through diet and produced in the body;
Participate in innumerable cellular functions;
Implicated in several health complications;
And blamed I am, for no fault of mine!”
Cholesterol
• Best known steroid because of its association with atherosclerosis
• biochemically of significance because it is the precursor of a large # of equally important steroids
1. Sex hormones 5. Cardiac glycosides
2. Bile acids 6. Sterols
3. Vit. D 7. Sitosterol
4. Adrenal cortical hormones 8. Alkaloids
Cholesterol in Perspective
Cholesterol has many roles in health and disease, both in its own right, and as a precursor of a variety of biologically, important substances.
Cholesterol
GallstoneAtherosclerotic
plaqueLipoproteins
Membranes
Hormones
Adrenal / gonadsBile Acids
Acetate
U V lightVit. D
ATHEROSCLEROSIS
• Cholesterol penetrates into the T. interna, narrowing the vessels decreasing blood supply causing M I
• cholesterol must be packaged as part of a LIPOPROTEIN in order to be transported in blood
• its insolubility makes deposit troublesome especially in atherosclerotic plaques and gallstones
• A high level of blood cholesterol, especially that contained in LDL is a risk in atherosclerotic disease, much attention is being given to factors that lower cholesterol levels
a) DIET– substitute vegetable products for meat and
dairy products– consume more Polyunsaturated fatty acids
that saturated products– has a cholesterol lowering effects
b) Exercise HDL / LDL ratio which correlates negatively
with Atherosclerosis
KETOGENESIS AND THE ROLE OF KETONE BODIES IN ENERGY METABOLISM
acetoneKetone bodies acetoacetate
-hydroxybutyrate
acetone TRUE ketonesacetoacetate
-hydroxybutyrate-does not possess a keto (C=0) group
Ketone bodies are water soluble and energy yielding
liver - synthesis occur
mitochondrial matrix - where enzymes for ketone bodies synthesis are located
oxidation of FA Acetyl CoA
pyruvate
some AA precursor for ketone
bodies
Reactions of Ketogenesis
1. Two moles of acetyl CoA condense to form acetoacyl CoA
• reaction catalyzed by Thiolase (an enzyme involved in the final step of -oxidation)
• hence acetoacetate synthesis is regarded as the reversal of thiolase reaction of fatty acid oxidation
2. Acetoacyl CoA combines with another molecule of acetyl CoA to produce -methyl glutaryl CoA (HMC CoA)
• HMG CoA synthase, catalyzing the reaction, regulates the synthesis of ketone bodies
3. HMG CoA lyase cleaves HMG CoA to produce acetoacetate and acetyl CoA
4. Acetoacetate can undergo spontaneous decarboxylation to form acetone
5. Acetoacetate can be reduced by a dehydrogenase to -hydroxybutyrate
The C skeletons of some AA (ketogenic, leucine, lysine, phenylalanine, etc.) is degraded to acetoacetate or acyl CoA and to ketone bodies
Energy yield from oxidation of ketone bodies
1. Conversion of -hydroxybutyrate to acetoacetate yields an NADH molecule, yields 3 ATP molecules (by electron transport and oxidative phosphorylation)
2. Each mole of acetyl CoA that is formed yields 12 moles of ATP (via citric acid cycle, electron transport, and oxidative phosphorylation)
3. The activation reactions require 1 mole of ATP.
4. Therefore, oxidation of acetoacetate yields 24 moles (from 2 moles of acetyl CoA) - 1 mole
ATP (expended during activation) = 23 moles of ATP
oxidation of -hydroxybutyrate yields
3 moles of ATP (from one NADH molecule) + 24 moles of ATP (from 2 moles of acetyl CoA) - mole of ATP = 26 modes of ATP
During prolonged starvation ketone bodies are the major fuel source for the brain and other parts of the CNS
• Ability of the brain to utilize FA for energy is limited
• ketone bodies can meet 50-70% of the brain’s energy needs
In No individuals constant production of ketone bodies (liver)– concentration in the blood 1 mg/dL– excretion in urine is very low and
undetectable by routine tests (Rothera’s test)
Ketonemia rate of synthesis of ketone bodies exceeds the rate of utilization, their concentration in the blood
Ketonuria follows ketonemia, secretion of ketone bodies in the urine
Ketonemia ketosis (overall picture)
Ketonuria (+) acetone breath associated
with starvation and severe
uncontrolled DM
Glucagon stimulates ketogenesisInsulin inhibits
Ketogenic substances (promote ketone body formation)
1. Fatty acids
2. Amino acids (leucine, lysine, tyrosine)
Antiketogenic substances (inhibits ketone body formation)
1. Glucose
2. Glycerol
3. Glucogenic AA (glycine, alanine, serine, glutamate)
Acetoacetate strong acids - when in -hydroxybutyrate concentration in the blood
cause ACIDOSIS
Diabetic acidosis dangerous coma death if untreated