Unit 2: Carbohydrate Metabolism

February 20, 2026

Semester 2
BP203T

Introduction to Carbohydrate Metabolism

Unit 2 is the biggest and most important unit in Biochemistry for students interested in pharmacology. It covers the complete breakdown of glucose, from Glycolysis to the Krebs Cycle and the Electron Transport Chain (the powerhouse of the cell). Understanding these pathways is key to understanding drugs for Diabetes and Metabolic disorders.

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Syllabus & Topics

  • 1Glycolysis: Complete pathway, enzymes, energetics (net ATP gain = 2), and biological significance.
  • 2Citric Acid Cycle (TCA/Krebs Cycle): Complete pathway, energetics, and significance.
  • 3HMP Shunt (Pentose Phosphate Pathway): Pathway, products, and significance (NADPH, pentoses).
  • 4Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency: Clinical significance.
  • 5Glycogen Metabolism: Glycogenesis (synthesis) and Glycogenolysis (breakdown) pathways.
  • 6Glycogen Storage Diseases (GSD): Types and examples (Von Gierke’s, Pompe’s disease).
  • 7Gluconeogenesis: Pathway (from non-carbohydrate sources: pyruvate, lactate, amino acids) and significance.
  • 8Hormonal regulation of blood glucose level: Insulin vs Glucagon.
  • 9Diabetes Mellitus: Type 1 and Type 2.
  • 10Biological Oxidation: Electron Transport Chain (ETC) – components and mechanism (Complex I-IV).
  • 11Oxidative Phosphorylation: Mechanism and ATP yield (Chemiosmotic theory by Mitchell).
  • 12Substrate Phosphorylation.
  • 13Inhibitors of ETC and Oxidative Phosphorylation.
  • 14Uncouplers of Oxidative Phosphorylation (e.g., DNP).

Learning Objectives

Draw Glycolysis: Write the complete Glycolysis pathway with enzymes and products at each step.
TCA Cycle: Identify the entry point, all intermediates, and the final products of one turn of the Krebs cycle.
Calculate Energy Yield: Calculate the total ATP produced from complete oxidation of one molecule of glucose (36-38 ATP).
Distinguish Glycogenesis/Glycogenolysis: Explain the key regulatory step in each pathway.
Explain Gluconeogenesis: Name 3 non-carbohydrate precursors for glucose synthesis.

Frequently Asked Questions (FAQs)

Q1. What is the net ATP gain from Glycolysis?

The net yield of glycolysis (occurring in the cytoplasm) from one glucose molecule is:

  • 2 ATP (net gain)

  • 2 NADH

  • 2 Pyruvate molecules

Q2. What is the significance of HMP Shunt?

The HMP Shunt (Pentose Phosphate Pathway) generates:

  • NADPH – required for biosynthesis and antioxidant defense

  • Ribose-5-phosphate – required for nucleotide synthesis

It is particularly active in the liver, red blood cells (RBCs), and adipose tissue.

Q3. What is G6PD Deficiency?

G6PD deficiency is a genetic disorder in which the glucose-6-phosphate dehydrogenase enzyme is deficient. As a result, RBCs cannot generate enough NADPH via the HMP shunt, making them vulnerable to oxidative damage. This can cause hemolytic anemia, often triggered by certain drugs such as primaquine.

Q4. What is Chemiosmotic Theory?

The Chemiosmotic Theory, proposed by Peter Mitchell, states that ATP is synthesized when protons (H⁺) flow back across the inner mitochondrial membrane through ATP synthase. This process is driven by the electrochemical gradient generated by the electron transport chain (ETC).

Q5. What are ETC Inhibitors?

Examples of ETC inhibitors include:

  • Rotenone – inhibits Complex I

  • Antimycin A – inhibits Complex III

  • Cyanide and Carbon monoxide (CO) – inhibit Complex IV

Uncouplers such as 2,4-Dinitrophenol (DNP) allow protons to bypass ATP synthase, causing energy to be released as heat instead of ATP.