All energy yielding process are ultimately dependent upon enzymatically catalyzed redox reactions. The most important one for energy metabolism involve biological membranes with bound electron transport processes like photosynthesis and oxidative phosphorylation. Biological oxidation is the primary provider of energy for cellular anabolism, the reductive synthesis of metabolites, by furnishing mobile hydrogens, and phosporylating energy by combining hydrogens with oxygen to form water coupling this process to the production of ATP in the form of oxidative phosphorylation. Central to the oxidation-reduction processes are the vitamin B group containing coenzymes nicotinamide-adenine dinucleotide (NAD) and nicotinamide-adenine dinucleotide phosphate ( NADP , (C00006; oxidized form); NAD (C00003; oxidized form; not phosphorylated at the adenosine ribosyl C2 position). Being part of the appropriate enzymes the oxidized nicotinamide ring of NAD + or NADP + extracts a hydride (H: - ) from a wide variety of simple metabolites in a process known as dehydrogenation . The enzymes catalyzing the reduction of nicotinamide containing coenzymes are called dehydrogenases . In a typical reaction two hydrogen atoms (including their electrons) are removed from the substrate to produce the oxidized form of the donor. The fate of the two hydrogens differs: one hydrogen with two electrons (H: - ), a hydride ion, is transferred to the nicotinamide ring to produce reduced NADH or NADPH while the other hydrogen is released into solution as a free proton (H + ). The generic form of a redox reaction mechanism catalyzed by enzymes with NAD as cofactor is shown.
Some of the drugs used to treat HIV patients are competitive inhibitors of the HIV reverse transcriptase enzyme. Unfortunately, the high mutation rate of HIV means that the virus rapidly acquires mutations with amino acid changes that make them resistant to these competitive inhibitors. Where in the reverse transcriptase enzyme would such amino acid changes most likely occur in drug-resistant viruses?
A) in or near the active site
B) at an allosteric site
C) at a cofactor binding site
D) in regions of the protein that determine packaging into the virus capsid
E) such mutations could occur anywhere with equal probability
In chemical thermodynamics , an endergonic reaction (also called a heat absorb nonspontaneous reaction or an unfavorable reaction ) is a chemical reaction in which the standard change in free energy is positive, and energy is absorbed. In layman's terms, the total amount of energy is a loss (it takes more energy to start the reaction than what you get out of it) so the total energy is a negative net result. For an overall gain in the net result see exergonic reaction . Another way to phrase this is that energy is absorbed from the surroundings into the workable system.