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18 Cards in this Set
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Describe adipose tissue (TAG) lipolysis and the regulation of hormone sensitive lipase (HSL).
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TAG is broken down to glycerol and NEFAs in white adipose tissue by hormone-sensitive lipase (HSL).
HSL is up-regulated by catecholamines (epi and norepi) which stimulate its phosphorylation. It is down-regulated by insulin which enhances its dephospohorylation form. |
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Indicate mechanism of fatty acid transport to the tissues.
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Both glycerol and NEFA diffuse out of the cell where the NEFA is attached to Albumin for transport to the tissues.
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Describe fatty acid activation
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A thioester bond is formed between the COOH group of a NEFA and the thiol group of Coenzyme A (CoA-SH)
Thiokinase (acyl-CoA synthetase) is the enzyme and is endergonic and so linked to ATP - ADP + Pi. |
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Describe the carnitine shuttle mechanism
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1. in the Outer Membrane - Acyl-CoA + carnitine → acyl-carnitine by CPT-1 (carnitine palmitoyl transferase I)
2. Acyl-carnitine passed through porin channel protein to intermembrane space. 3. Inner Membrane bound acyl-carnitine translocase passes acyl-carnitine into the matrix with the enzyme CPT II (carnitine palmitoyl transferase II) 4. CoA is converted to Acyl-CoA in the matrix 5. Carnitine is passed through the membrane by the same translocase. |
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Explain the biochemical consequences of defects in transport of fatty acids (carnitine deficiency and CPT deficiency)
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CPT 1 Deficiency - affects liver, reduced FA oxidation, hypoketotic, hypoglycaemic, probably lethal
CPT II Deficiency - affects skeletal/cardiac muscle, cardiomyopathy, muscle pain, cramps (after exercise), muscle necrosis (myoglobinuria) Acyl-carnitine translocase deficiency - muscle weakness, hypoglycaemic, hyperammonaemic & cardiomyopathy. Fatal in infancy. Plasma membrane (OCN-2) carnitine transporter deficiency (in muscle) - Myopathic Carnitine Deficiency (Systemic carnitine deficiency) - defective sodium-dependent transport. Low intracellular carnitine levels, compromised acyl-oxidations in tissues, mild cramps to severe weakness. Secondary carnitine deficiency - metabolic, not inheritable, defects in beta-oxidation pathway lead to acyl-carnitine accumulation which are excreted from the kidneys. |
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List the reactions of the mitochondrial beta-0xidation pathway (not substrate names)
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Fatty acyl CoA
1. Acyl CoA Dehydrogenase (oxidation) 2. Enol CoA hydratase (hydration) 3. 3-Hydroxyacyl CoA dehydrogenase (oxidation) 4. beta-Ketoacyl-CoA thiolase (cleavage requiring 2 CoA) Fatty acyl CoA and Acetyl CoA |
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Outline the energetics of beta-oxidation
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1. Divide the number of carbons in half
2. That is the number of Acetyl-CoAs made 3. Subtract one for the number of FADH2 and NADH 4. Each Acetyl CoA = 12 ATP, FADH2 = 2 ATP, NADH = 3 ATP |
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Indicate the end products of oxidation of odd chain fatty acids
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The final acyl group is a 3-C propionyl-CoA. It is converted to succinyl-CoA.
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indicate the biochemical defect in Refsum's disease
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Refsum's disease (phytanic acidstorage syndrome) is the result of the inability to metabolise phytanic acid and its aggregation in tissue and blood.
Cause - Autosomal recessive Symptoms - progressi ve neurolgical difficulties (tremors, unsteady gain and poor night vision) Pathology - segmental demyelination of peripheral nerves with hypertrophy second to Schwann cell proliferation Treatment - strict dietary management avoiding green vegetables. |
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Distinguish between medium-chain acyl-CoA dehydrogenase deficiency and Jamaican vomiting sickness based on the pathogenetic mechanism and biochemical alterations
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Med-Chain Acyl-CoA dehydrogenase deficiency (MCAD) is a congenital deficiency where this enzyme is missing.
Jamaican Vomiting Sickness is a result of the toxin in unripe akee fruit. The toxin is an irreversible inhibitor of short and medium chain acyl-CoA dehydrogenases. |
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Outline peroxisomal alpha- and beta-oxidation
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Peroxisomal alpha-oxidation reduces fatty acids one carbon at a time.
??????????? Peroxisomal beta-oxidation specifically oxidized VLCFAs. ???????????????? |
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Discuss Zellweger's syndrome as a disorder of peroxisomes
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Defective peroxins (proteins for peroxisomal biogenesis) lead to an absence of peroxisomes. VLCFAs accumulate in plasma and tissues and become toxic in the CNS.
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Describe the pathway of hepatic ketogenesis and list the ketone bodies
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Acetone - Acetoacetate - β-hydroxybutyrate
1. Ketothiolase condenses 2 acetyl-CoAs into Acetoacetyl-CoA 2. It condenses with another acetyl-CoA to form β-hydroxy-β-methylglutaryl-CoA (HMG-CoA) 3. HMG-CoA Lyase removes an acetyl-CoA forming Acetoacetate. 4. Acetoacetate may undergo spontaneous decarboxylation in the blood to form acetone. |
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Explain ketone body utilization in peripheral tissues
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Acetoacetate can be reconverted to acetyl-CoA once you are out of the liver. It is catalyzed by syccinyl-CoA:acetoacetate-CoA (thiophorase). The brain uses this during periods of starvation as ketonebodies can pass the blood-brain barrier.
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Prepare a concept map indicating the steps involved in the generation of ketosis in starvation and uncontrolled type 1 diabetes mellitus
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X
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Correlate laboratory data in ketoacidosis (laboratory data in blood and urine) to the clinical signs in the patient; including hyperventilation
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Outline oxidation of branched chain fatty acids
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1. Peroxisomal oxidation removes single carbons from branched fatty acids until they are unbranched.
2. The fatty acid is passed to the beta-oxidation pathway (peroxisomal or not) |