Questions
2–4 questions per semester paper
Difficulty
Medium-Hard
Importance
High yield for University theory and clinical vivas
Overview
Metabolism covers the complex biochemical pathways through which the body processes macronutrients to sustain life and energy balance. Understanding these pathways—Glycolysis, the Urea Cycle, and Beta-Oxidation—is essential for answering clinical biochemistry questions in nursing and medical board examinations.
Carbohydrate Metabolism
This pathway focuses on the catabolism of glucose to generate ATP and the regulation of blood sugar levels. Mastery of Glycolysis and the TCA cycle is mandatory as they are the primary energy-yielding mechanisms in cellular respiration.
- Glycolysis: Glucose to Pyruvate (occurs in cytoplasm)
- TCA Cycle: Acetyl-CoA oxidation (occurs in mitochondria)
- Glycogenesis: Formation of glycogen from glucose
- Glycogenolysis: Breakdown of glycogen to glucose
- Gluconeogenesis: Synthesis of glucose from non-carbohydrate sources
Protein Metabolism
Proteins are broken down into amino acids, which undergo transamination and deamination before being processed for energy or nitrogen disposal. The urea cycle is the critical biological mechanism for neutralizing toxic ammonia into urea for excretion.
- Transamination: Transfer of amino group to alpha-keto acid
- Oxidative Deamination: Release of nitrogen as ammonia
- Urea Cycle: Occurs primarily in the liver
- Essential vs Non-essential amino acids
- Nitrogen Balance: Intake vs output status
Lipid Metabolism
Lipids provide the most concentrated source of energy through the beta-oxidation of fatty acids. This process produces Acetyl-CoA, which feeds into the TCA cycle to generate a high yield of ATP.
- Beta-oxidation: Sequential removal of 2-carbon units from fatty acids
- Lipogenesis: Synthesis of fatty acids from Acetyl-CoA
- Ketogenesis: Formation of ketone bodies during starvation
- Role of Carnitine shuttle in fatty acid transport
- High-density vs Low-density lipoproteins (HDL/LDL)
Formula Sheet
Glucose + 2NAD+ + 2ADP + 2Pi -> 2Pyruvate + 2NADH + 2ATP + 2H2O
NH3 + CO2 + Aspartate -> Urea + Fumarate
Exam Tip
Always draw a schematic flow chart linking the three metabolisms through the common intermediate Acetyl-CoA to score maximum marks in long-form questions.
Common Mistakes
- Confusing the location of pathways (e.g., placing Glycolysis in mitochondria instead of cytoplasm)
- Failing to mention the rate-limiting enzymes like PFK-1 in Glycolysis
- Ignoring the distinction between aerobic and anaerobic end-products
More Revision Notes
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