HMP Shunt & Others

HMP Shunt & Other Pathways

The Hexose Monophosphate (HMP) Shunt, also called the Pentose Phosphate Pathway (PPP), is an alternative pathway for glucose-6-phosphate oxidation. It does NOT produce ATP directly but generates two essential products: NADPH and Ribose-5-phosphate.

Location & Tissues

Cytosol. Most active in tissues with high biosynthetic activity: Liver (FA synthesis), Adipose tissue, Adrenal cortex (steroid synthesis), RBCs (antioxidant defense), Mammary gland, and Gonads (steroidogenesis).

Two Phases

Oxidative Phase (irreversible):

  1. G6P → 6-Phosphogluconolactone + NADPH [G6PD — rate-limiting, NADP+ activates]
  2. 6-Phosphogluconolactone → 6-Phosphogluconate [Lactonase]
  3. 6-Phosphogluconate → Ribulose-5-P + CO₂ + NADPH [6-Phosphogluconate dehydrogenase]

Net: 1 G6P + 2 NADP+ → 1 Ribulose-5-P + 2 NADPH + CO₂

Non-oxidative Phase (reversible — Transketolase and Transaldolase reactions): Interconverts pentose phosphates with glycolytic intermediates (F6P, G3P). Allows return to glycolysis if ribose-5-P is not needed.

NADPH Functions

  • Reductive biosynthesis: Fatty acid synthesis, Cholesterol synthesis, Steroid hormone synthesis
  • Antioxidant defense: Maintains Glutathione in reduced form (GSH) via Glutathione reductase
  • Phagocyte NADPH oxidase: Produces superoxide (O₂•⁻) to kill bacteria (Respiratory burst)
  • Cytochrome P450 reactions (drug metabolism)
  • Nitric oxide synthase (NO production)

G6PD Deficiency

Most common enzyme deficiency worldwide (X-linked recessive; more common in African, Mediterranean, Asian populations). RBCs cannot maintain GSH → oxidative stress → Heinz bodies form → hemolysis.

Triggered by: Primaquine (antimalarial), Dapsone, Fava beans, infections, naphthalene (moth balls). Presents as: episodic hemolytic anemia, jaundice.

Fructose Metabolism

  • In Liver: Fructose → Fructose-1-P [Fructokinase] → DHAP + Glyceraldehyde [Aldolase B] → enters glycolysis
  • Bypasses PFK-1 regulation → unregulated entry into glycolysis → FA synthesis, lactic acidosis
  • Essential Fructosuria: Fructokinase deficiency; benign
  • Hereditary Fructose Intolerance: Aldolase B deficiency; F1P accumulates → liver damage, hypoglycemia (severe; avoid fructose and sucrose)

Galactose Metabolism

Galactose → Galactose-1-P [Galactokinase] → UDP-Galactose [GALT enzyme] → UDP-Glucose [Epimerase]. Used for lactose synthesis in mammary gland and glycoprotein/glycolipid synthesis.

Classic Galactosemia: GALT deficiency → Gal-1-P accumulates; also galactitol (via aldose reductase) → cataracts; liver cirrhosis; intellectual disability; E. coli sepsis in neonates.

Quiz - Exam Preparation Strategy

When studying Quiz for your final board exams, it is critical to focus on the core concepts and fundamental formulas. Relying strictly on NCERT textbook solutions and practicing previous year questions (PYQs) is the proven methodology for scoring high marks. Avoid rote memorization and instead focus on the logical application of the theories presented in this chapter.

⚠️ Common Mistakes to Avoid

❓ Frequently Asked Questions

How can I quickly memorize the concepts of Quiz?

The most effective way is to create short, handwritten revision notes and continuously test your knowledge using our interactive Mock Tests. Spaced repetition and active recall are much better than passive reading.

What type of questions are most commonly asked from Quiz?

Board exams tend to favor conceptual application questions and direct formula-based derivations from the NCERT syllabus. Ensure you have solved every single exercise in the official textbook.

Is reading the NCERT book enough for this chapter?

Yes, the NCERT textbook is the absolute gold standard for board exams. However, to improve your speed and accuracy during the actual exam, you must supplement your reading by solving timed mock tests and objective questions.