ATP & Respiration: Crash Course Biology In which Hank does some push ups for science and describes the "economy" of cellular respiration and the various processes whereby our bodies create energy in the form of ATP.
The tricarboxylic acid (TCA) cycle (also known as thecitricacid cycle or the Kreb's cycle): when an organic compound is utilizedasa substrate, the TCA cycle is used for the complete oxidation of thesubstrate.
[The evidence seems incontrovertible that mitochondria evolved from bacteria or
prokaryotes internalised by ancestral cells - mitochondria are evolved bacteria that can no longer live without their host cell
and vice versa.] Organic fuels such as glucose are oxidised in the cytosol (by a complex series of chemical reactions called
glycolysis and Kreb's cycle) removing hydrogen atoms from them.
1. Prior to entering the Krebs Cycle, pyruvate must be converted into acetyl CoA. This is achieved by removing a CO2 moleculefrom pyruvate and then removing an electron to reduce an NAD+ into NADH. An enzyme called coenzyme A is combined with the remaining acetyl tomake acetyl CoA which is then fed into the Krebs Cycle. The steps in the KrebsCycle are summarized below:
The host cell can not make ATP by electron transport in aerobic respiration without
mitochondria, but it does carry out glycolysis in the cytosol and then transports the end product, pyruvate, into the
mitochondria where it is used in Kreb's cycle which takes place in the mitochondrial matrix (the 'mitochondrial cytosol').
glycolysis does not provide as much energy as aerobic respiration, indeed in aerobic
respiration, pyruvate produced by glycoslysis is further oxidised by the Kreb's cycle and by the ETS, involving oxygen as the
final oxidant or terminal electron acceptor.