Question

What is the role of mitochondria in respiration?

Answer 1

Hint: Mitochondria (singular-mitochondria) or chondriosomes are large cell organelles of aerobic eukaryotes which are centres of Krebs cycle and oxidative phosphorylation. They were discovered by Kolliker (1850, 1880) as granules (sarcosomes) in muscle cells. Flemming (1882) and Altman (1886) also studied them and gave different names to them, Benda (1897) stained them with alizarin and crystal violet. He coined the term mitochondria.

Complete answer:
A mitochondrion is covered by a double membrane envelope which encloses a highly involuted inner core or inner chamber. There is an outer and an inner membrane in the envelope. Each of the two membranes of the mitochondrial envelope is 60-75 A in thickness. They enclose a narrow peri mitochondrial space called the outer chamber. The latter develops a number of ingrowths in the inner chamber.
Outer Membrane. It is a smooth membrane which is chemically 40% lipid and 60% protein. The lipids are mainly phospholipids and cholesterol. Cardiolipin content is low. Membrane enzymes are fewer (e.g., Monoamine oxidase. NADH-Cyt c reductase, Fatty acid CoA ligase, Kyneurinine hydroxylase).
Inner Membrane. It is a selectively permeable membrane which is rich in proteins (80%). Lipid contact is 20%. Phospholipid content is 1/3, cholesterol content 1/6 while cardiolipin content is nearly 7 times more as compared to outer membrane.
Mitochondria perform the Krebs cycle or tricarboxylic acid cycle of aerobic respiration. Oxygen is used as a terminal oxidant. CO₂ and water are produced. Terminal oxidation takes place through oxidative phosphorylation. It produces ATP. Even the reduced coenzymes produced in cytosol through glycolysis transfer their reducing power to mitochondria for ATP synthesis. ATP synthesised inside mitochondria provides energy for all cellular activities including overcoming the tendency for entropy. Therefore, mitochondria are called power houses of the cell.

Note:
In animal cells, mitochondria are the second largest cell organelles. In plant cells they have the third largest size. Commonly mitochondria are 1-0-4-1 um in length and 0-2-1-0 μm (average 0-5 um) in diameter. Large mitochondria of 10 um length occur in pancreatic cells. The common shape is cylindrical or sausage-tubular. It is spherical in Yeast. Other forms are filamentous, club-shaped, racket-shaped or vesicular. Mitochondrion is tubular and branched in Chlorella. Chemical composition: Proteins: 60-70%, lipids: 25-35%, RNA: 5-7%, DNA-small amount, Minerals-traces.