**Inquiry and Analysis: Do Enzymes Physically Attach to Their Substrates?** When scientists first began to examine the chemical activities of organisms, no one knew that biochemical reactions were catalyzed by enzymes. The first enzyme was discovered in 1833 by French chemist Anselme Payen. He was studying how beer is made from barley: First, barley is pressed and gently heated so its starches break down into simple two-sugar units; then yeasts convert these units into ethanol. Payen found that the initial breakdown requires a chemical factor that is not alive and that does not seem to be used up during the process—a catalyst. He called this first enzyme diastase (we call it amylase today). Did this catalyst operate at a distance, increasing the reaction rate all around it, much as raising the temperature of nearby molecules might do? Or did it use physical contact, actually attaching to the molecules whose reaction it catalyzed (its “substrate”)? The answer was discovered in 1903 by French chemist Victor Henri. He saw that the hypothesis that an enzyme physically binds to its substrate makes a clear and testable prediction: In a solution of substrate and enzyme, there must be a maximum reaction rate. When all the enzyme molecules are working full tilt, the reaction simply cannot go any faster, no matter how much more substrate you add to the solution. To test this prediction, Henri carried out the experiment whose results you see in the graph, measuring the reaction rate (V) of diastase at different substrate concentrations (S). **Analysis** 1. **Making Inferences**: As S increases, does V increase? If so, in what manner—steadily, or by smaller and smaller amounts? Is there a maximum reaction rate? 2. **Drawing Conclusions**: Does this result provide support for the hypothesis that an enzyme binds physically to its substrate? Explain. If the hypothesis were incorrect, what would you expect the graph to look like? 3. **Further Analysis**: If the smaller amounts by which V increases are strictly the result of fewer unoccupied enzymes being available at higher values of S, then the curve in Henri’s experiment should show a pure exponential decline in V—mathematically, meaning a reciprocal plot (1/V versus 1/S) should be a straight line. If some other factor is also at work that reacts differently to substrate concentration, then the reciprocal plot would curve upward or downward.
Electron Transport Chain
The electron transport chain, also known as the electron transport system, is a group of proteins that transfer electrons through a membrane within mitochondria to create a gradient of protons that drives adenosine triphosphate (ATP)synthesis. The cell uses ATP as an energy source for metabolic processes and cellular functions. ETC involves series of reactions that convert redox energy from NADH (nicotinamide adenine dinucleotide (NAD) + hydrogen (H)) and FADH2(flavin adenine dinucleotide (FAD)) oxidation into proton-motive force(PMF), which is then used to synthesize ATP through conformational changes in the ATP synthase complex, a process known as oxidative phosphorylation.
Metabolism
Picture a campfire. It keeps the body warm on a cold night and provides light. To ensure that the fire keeps burning, fuel needs to be added(pieces of wood in this case). When a small piece is added, the fire burns bright for a bit and then dies down unless more wood is added. But, if too many pieces are placed at a time, the fire escalates and burns for a longer time, without actually burning away all the pieces that have been added. Many of them, especially the larger chunks or damp pieces, remain unburnt.
Cellular Respiration
Cellular respiration is the cellular process involved in the generation of adenosine triphosphate (ATP) molecules from the organic nutritional source obtained from the diet. It is a universal process observed in all types of life forms. The glucose (chemical formula C6H12O6) molecules are the preferred raw material for cell respiration as it possesses a simple structure and is highly efficient in nature.
Enzyme are usually protein molecules that are highly specific to their substrate. These are biological catalyst as they catalyse a particular reaction without being itself used up in the reaction. These increase the rate of a reaction.
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