Q.Give a detailed account of the ultrastructure and functions of mitochondria and plastids, and explain the endosymbiotic theory of their evolutionary origin together with the structural evidence that supports it.
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Start your 14-day free trial to unlock the full solution →Mitochondria, the "powerhouse of the cell," are bound by two membranes: a smooth outer membrane, and an inner membrane thrown into folds called cristae that project into the central matrix, greatly increasing the membrane surface available for the reactions of aerobic respiration; oxysomes (F1 particles) studding the cristae are the actual sites of ATP synthesis. The perimitochondrial (intermembrane) space lies between the two membranes, and the matrix contains the enzymes of respiration along with the organelle's own small circular DNA and its own 70S ribosomes. Because of this DNA and ribosome set, a mitochondrion can synthesise some of its own proteins and divide independently, though it still depends on the nucleus for most of its proteins.
Plastids -- chloroplasts, chromoplasts and leucoplasts -- are likewise double-membrane-bound. The chloroplast, site of photosynthesis, has an outer and inner envelope enclosing a fluid stroma, within which a system of flattened thylakoid discs is stacked into grana, connected to one another by stroma lamellae; the thylakoid membranes carry out the light reactions of photosynthesis, while the stroma houses the enzymes of the Calvin cycle. Like the mitochondrion, the chloroplast contains its own circular DNA and its own 70S ribosomes, making it equally semi-autonomous. …
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