Narwani's Biology Globe

24/05/2026

XII Biology, test from MDCAT syllabus

16/05/2026

16/05/2026

Electron Transport Chain (ETC) — Respiration

The Electron Transport Chain (ETC) is the final stage of aerobic respiration and occurs on the inner mitochondrial membrane (cristae).

Its main function is to:

Transfer electrons from NADH and FADH₂

Pump protons (H⁺) across the membrane

Create a proton gradient

Produce ATP by oxidative phosphorylation

Main Components of ETC

Complex I — NADH Dehydrogenase

Receives electrons from NADH

Pumps protons into intermembrane space

Complex II — Succinate Dehydrogenase

Receives electrons from FADH₂

Does not pump protons

Coenzyme Q (Ubiquinone)

Transfers electrons from Complex I & II to Complex III

Complex III — Cytochrome bc₁ Complex

Pumps protons

Cytochrome c

Transfers electrons to Complex IV

Complex IV — Cytochrome Oxidase

Transfers electrons to oxygen

Oxygen combines with electrons and H⁺ to form water

ATP Synthase (Complex V)

Uses proton flow to synthesize ATP

Oxygen is the final electron acceptor.

Proton Pumping in ETC

Complex Protons Pumped

Complex I 4 H⁺
Complex II 0 H⁺
Complex III 4 H⁺
Complex IV 2 H⁺

Total Proton Pumping

From 1 NADH = 10 H⁺

From 1 FADH₂ = 6 H⁺

ATP Production

✅ 1 NADH produces about 2.5-3 ATP

✅ 1 FADH₂ produces about 1.5-2 ATP

Total ATP from ETC

Key Points for MDCAT

ETC occurs in inner mitochondrial membrane

Oxygen is the final electron acceptor

ATP formation here is called oxidative phosphorylation

NADH enters at Complex I

FADH₂ enters at Complex II

Complex II does not pump protons

ATP synthase uses proton gradient to make ATP

1 NADH → 3 ATP

1 FADH₂ → 2 ATP

16/05/2026

Homeostasis MDCAT

15/08/2025

Calcium homeostasis
Role of Calcitonin & PTH

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Phosphodiester Bond in polynucleotide