Metabolic Tips: WHILE YOU READ BIOCHEMISTRY SCAN FOR THE FOLLOWING tips

1. Three compulsory lists that must be at your tips-

• Ketogenic and Glucogenic amino acids.
• Essential and Nonessential amino acids.
• Basic, Acidic, Sulphur containing amino acids.

2. Regulatory Enzymes of pathways e.g.

• Citrate synthesis in citric acid cycle.
• Phosphofructokinase in Glycolysis.
• Pyruvate dehydrogenase in Pyruvate Oxidation.
• Pyruvate Carboxykinase in Gluconeogenesis.
• Glycogen Synthase in Glycogenesis.
• Phosphorylase in Glycogenolysis.
• G6PD in PPP.  
• HMG CoA reductase in cholesterol synthesis.

3. Search for ATP estimates e.g.,

• 8 ATP’s per Glucose molecule in Glycolysis under aerobic conditions.
• 30 ATP’s per Pyruvate molecule entering citric acid cycle.
• 129 ATP’s per palmitate undergoing b-oxidation.

4. Look for regulatory molecules and feedback inhibitions e.g.,

• Glucose-6-phosphate inhibition on hexokinase.
• Citrate’s inhibitory effect on phosphofructokinase 1.
• Alanine’s inhibitory effect on Pyruvate kinase.
• Acetyl CoA’s inhibitory effect on Pyruvate dehydrogenase.
• Long chain acyl CoA’s inhibitory effect on Acetyl CoA carboxylase.

5. Look for subcellular organelles where the reactions specifically occur.

• Enzymes of citric acid cycle in mitochondrial matrix.
• Enzymes of Glycolysis in cytosol.
• Enzymes of pentose phosphate pathway in cytosol.
• Enzymes of denovo synthesis of fatty acids in cytosol.
• Enzymes of fatty acid oxidation in mitochondria.

6. Always have a clarity regarding precise role of various lipoproteins.

• HDL is cholesterol scavenger.
• Chylomicrons carry dietary cholesterol.
• VLDL are vehicles of transport of triacylglycerol from the liver to extrahepatic tissues.

7. Vitamins and their role as coenzymes e.g.,

• Thiamine in oxidative decarboxylation.
• Niacin in dehydrogenase reactions.
• Pantothenic acid in CoA.
• Pyridoxal phosphate in muscle phosphorylase.
• Biotin in carboxylase enzymes.
• Vitamin B12 to produce succinyl CoA.
• Folate in transfer of one-carbon units.

8. Products that accumulate in metabolic disorders e.g.,

• Homogenisate in urine of Alkaptonuria patients
• Phenyl acetyl glutamine in phenylketonuria.
• Xanthurenate in Vitamin B6 deficiency.
• Branched chain ketonuria in Mapple syrup urine disease.

9. Check for key enzymes responsible for Metabolic disorders e.g.,

• Glucose-6-phosphates in von Gierkes.
• Hepatic fructokinase in essential fructosuria.
• Galactose-1-phosphate uridyl transferase in Galactosemia.
• Cystathionine-b-synthase in homocystinuria.

10. Where NADH forms, where NADPH forms, where FADH₂ forms, where substrate level phosphorylation occurs e.g.,

• FADH₂ in succinate dehydrogenase in citric acid cycle.
• NADH in all degradative reactions.
• NADPH in all synthetic reactions.