Difference of chemiosmosis in chloroplasts and mitochondria
Cellular energy metabolism features a series of redox reactions. Heterotrophs oxidize(take electrons from) organic molecules (food) and reduce (give them to) an electron carrier molecule, called NAD+ (in the oxidized form) that accepts electrons from food to become NADH (the reduced form). NADH then cycles back to NAD+ by giving electrons to (reducing) the first complex of the membrane electron transport chain. Thus NAD+/NADH is a key intermediary in shuttling electrons from food molecules to the electrons transport chain for respiration.
ATP & Respiration: Crash Course Biology #7 - YouTube
Oxidative phosphorylation synthesizes the bulk of a cell’s ATP during cellular respiration. A , in the form of a large proton concentration difference across the membrane, provides the energy for the membrane-localized (a molecular machine) to make ATP from ADP and inorganic phosphate (Pi). The proton gradient is generated by a series of oxidation-reduction reactions carried out by protein complexes that make up an electron transport chain in the membrane. The term oxidative phosphoryation, then, refers to phosphorylation of ADP to ATP coupled to oxidation-reduction reactions.
The earliest cells, prokaryotes living in an early Earth devoid of free oxygen, used various alternative electron acceptors to carry on anaerobic cellular respiration. After cyanobacteria invented oxygenic photosynthesis and pumped oxygen gas into the oceans and atmosphere, bacteria that adapted their electron transport chains to exploit oxygen as the terminal electron acceptor gained higher energy yield and thus a competitive advantage. One line of aerobic bacteria took up an endosymbiotic relationship within a larger host cell, providing ATP in exchange for organic molecules. The endosymbiont was the evolutionary ancestor of mitochondria. This endosymbiosis must have occurred in the ancestor of all eukaryotes, because all existing eukaryotes have mitochondria (Martin and Mentel, 2010). The evidence for the endosymbiont origin of mitochondria can be found in: