1- The type of phosphorylation in which a phosphate is directly transferred from

Question

1- The type of phosphorylation in which a phosphate is directly transferred from one organic molecule to another is called
______ level phosphorylation.
The type of phosphorylation in which an inorganic phosphate is transferred to an organic molecule is called
______ phosphorylation.

2- Discuss how cytosolic pyruvate gets into a mitochondrion.

3- Completely describe the phases of aerobic respiration in a eukaryotic cell, beginning with glycolysis and concluding with
the electron transport chain.

Explanation / Answer

2. Pyruvate dehydrogenase and carboxylase enzymes is localized in the mitochondrial matrix and, therefore, pyruvate has to be transported from cytosol through both the outer and the inner mitochondrial membranes. Similar to most other ions and metabolites, pyruvate traverses the outer mitochondrial membrane through the large, relatively non-specific, voltage-dependent anion channel or porin Consistent with this, humans deficient in VDAC1 shows in impaired pyruvate oxidation and ATP production As the proton gradient across the inner mitochondrial membrane has to be maintained for ATP production to occur, and diffusion of pyruvic acid across this membrane would collapse this gradient, logically there should be a transport mechanism with a proton symport. How pyruvate is transported through the IMM is still not sure and is still under research

It was suggested that pyruvate in its undissociated (acidic) forms can cross the IMM freely This seemed to contradict the consensus that the IMM was a selective barrier for other metabolites and, shortly after this, strong evidence was presented that pyruvate crossed the membrane via a specific transporter. Pyruvate transport display saturation kinetics for the existence of a specific transporter. The absorption of pyruvate into the membrane, rather than transport through it, accounted for mitochondrial pyruvate binding. This theory of pyruvate absorption by the membrane was later rejected . Regardless of these findings, without specific inhibitors of pyruvate transport, this cast doubt on the existence of carrier-mediated mitochondrial pyruvate transport.

3

Four stages of cellular respiration.

4. Oxidative phosphorylation- is the process in which ATP is formed as a result of the transfer of electrons from NADH or FADH 2 to O 2 by a series of electron carriers. This process, which takes place in mitochondria, is the major source of ATP in aerobic organisms

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