Question

You are studying a bacterial strain that is an obligate aerobe. The bacteria can do some fermentation and produce lactic acid as an end product, but normally only when starved for oxygen and can’t survive on fermentation alone. Your rival dumps a chemical into your prize culture. This chemical binds to the first protein in the electron transport chain, locking it into a fully reduced and inhibited state permanently. Describe the predicted consequences of this poison on the function of the following proteins or pathways. In each case, in 1-2 sentences describe: How the process normally works. How the process is affected by the poison initially (as the poison first acts) How the process is affected by the poison in the long term. Glycolysis: Krebs cycle: ATP Synthase: ( In the end, can this bacteria survive in the presence of this chemical? Yes or No

Answer 1

Mitochondrial inner membrane has Electron transport chain complexes. It consists of 4 cpmplexes. Complex I,II,III,IV.

NADH which is produced by glycolysis, oxidation of pyruvate and Kreb's cycle gets oxidized by first complex in the ETC. The first complex consists of NADH reductase which pumps two H+ ions in to the intermembrane space and two electrons in to the FMN present in the first complex. It also has Fe-S in the first complex which receive electrons from FMN. The electrons are then passed on to Coenzyme Q which is mobile carrier, carrying the electrons to complex III.

CoQ also pickes up 2 H+ ions and becomes CoQH2 which is soluble in lipid membrane and reaches the Complex III to pass on electrons in to it while the H+ ions are pumped in to the intermembrane space. The electrons are passed through the complex III which is also called the Cytochrome reductase complex bc. The electrons pass from cytochrome b1, b2,Fe-S, c1 and finally to c in the complex III. The electrons transported in to a small mobile carrier called Cytochrome c which also takes H+ ions along wiht the electrons from complex III. The H+ ions are channeld to the intermembrane space where as electrons are carried in to complex IV. The electrons from complex IV ultimately accepted by O2 to form H2O. The protons that are pumped in to the intermembrane space are pumped back in to matrix through a tunnel in the ATP synthase complex. The energy released is used in making 3 ATP molecules.

The complex I will take up electrons and H+ ions from NADH and oxidize the it under normal conditions. If the protein is already reduced, it can't take electrons from NADH. Then the NADH molecules will remain as reduced and hence ATP molecules can't be produced from NADH. This is th eimmediate effect.

Long term effect would be , there will not be enough NAD+ ions to make NADH in various steps of the glycolysis and Kreb's cycle. Because NAD+ gets reduced during these processes and oxidizes the substrate.

So the glycolysis and Krebs cycle can't go on for ever because of the lack of NAD+ ions. The amount of ATP produced will also be much less as NADH can't be oxidized.

In the presence of such a poison, the bacteria will not be able to survive.