Mitochondria
மைட்டோகாண்ட்ரியா
Mitochondria are not just powerhouses; they are endosymbiotic survivors. They retain their own circular DNA and 70S ribosomes, distinct from the host cell's nuclear genome. If you confuse their structural origin with the endomembrane system, you lose marks.
The idea
Mitochondria are double-membrane-bound organelles. The inner membrane folds into cristae to increase the surface area for biochemical reactions. The matrix contains enzymes for the Krebs cycle and single circular DNA. They are the primary sites of aerobic respiration, producing ATP.
Why it matters
They exist to convert chemical energy from food into ATP, which is the universal energy currency required for all cellular activities.
NEET lens
Expect questions on the cristae function and the composition of the matrix. NEET frequently tests the 'semi-autonomous' nature of mitochondria due to their own DNA. Memorize that the inner membrane is the site of the Electron Transport System (ETS). Do not confuse mitochondrial matrix enzymes with those in the cytoplasm.
Clinical significance
Mitochondrial DNA mutations lead to severe metabolic disorders like MELAS syndrome. When oxidative phosphorylation fails, high-energy tissues like the brain and skeletal muscles suffer immediate necrosis. Cellular energy failure is the hallmark of these pathologies.
Introduction
Mitochondria are double-membrane bound organelles that produce ATP through aerobic respiration (oxidative phosphorylation). They have their own DNA and ribosomes.
Core concept
Structure: outer membrane (smooth), inner membrane (folded into cristae — increases surface area), matrix (contains DNA, ribosomes, enzymes). Size: 0.5–10 μm. Number: varies (few in RBC, thousands in muscle cells). Cristae: site of electron transport chain. Matrix: site of Krebs cycle.
Go deeper
Endosymbiotic theory: Mitochondria originated from alpha-proteobacteria engulfed by ancestral eukaryote. Evidence: own circular DNA, 70S ribosomes (bacterial type), double membrane, binary fission reproduction.
From Class 10
You know cells have organelles. Mitochondria are the 'powerhouses' — they produce ATP energy through respiration.