Enzymes, biological catalysts

Not only do enzymes allow otherwise slow reactions to occur at a reasonable rate, they also allow living organisms to have tremendous control over which reactions occur and when. Enzymes are extremely specific—each enzyme catalyzes only a single reaction. So to turn a particular reaction on, a living organism simply needs to produce or activate the correct enzyme to catalyze that reaction. 

The Concept of Equilibrium Equilibrium involves the ideas of sameness and constancy. When a system is in equilibrium, some property of the system remains the same and does not change. The Concept of Equilibrium The equilibrium concept explains many phenomena such as the human body s oxygen delivery system. Life itself can be defined as controlled disequilibrium with the environment. 

Rates of Chemical Reactions The rate of a chemical reaction is the amount of reactant(s) that goes to prod-uct(s) in a given period of time. In general, reaction rates increase with increasing reactant concentration and increasing temperature. Since reaction rates depend on the concentration of reactants, and since the concentration of reactants decreases as a reaction proceeds, reaction rates usually slow down as a reaction proceeds. Rates of Chemical Reactions The rate of a chemical reaction determines how fast a reaction will reach its equilibrium. Chemists want to understand the factors that influence reaction rates so that they can control them. 

Dynamic Chemical Equilibrium Dynamic chemical equilibrium occurs when the rate of the forward reaction equals the rate of the reverse reaction. Dynamic Chemical Equilibrium When dynamic chemical equilibrium is reached, the concentrations of the reactants and products become constant. 

The Equilibrium Constant For the generic reaction aA + bB K cC + dD the equilibrium constant Kgq) is defined as [C] [D] Only the concentrations of gaseous or aqueous reactants and products are included in the equilibrium constant—the concentrations of solid or liquid reactants or products are omitted. The Equilibrium Constant The equilibrium constant is a measure of how far a reaction will proceed. A large Keq means the forward reaction is favored (lots of products at equilibrium). A small K q means the reverse reaction is favored (lots of reactants at equilibrium). An intermediate Kgq means that there will be significant amoimts of both reactants and products at equilibrium. 

An enzyme is typically a large protein molecule that contains one or more active sites where interactions with substrates take place. These sites are structurally compatible with specific substrate molecules, in much the same way that a key fits a particular lock. In fact, the notion of a rigid enzyme structure that binds only to molecules whose shape exactly matches that of the active 

The mathematical treatment of enzyme kinetics is quite complex, even when we know the basic steps involved in the reaction. A simplified scheme is given by the following elementary steps  

In general, the rate of such a reaction is given by the equation 

EmU Fischer (1852-1919). German chemist Regarded by many as the greatest organic chemist of the nineteenth century. Fischer made many significant contributions in the synthesis of sugars and other important molecules. He was awarded the Nobel Prize in Chemistry in 1902. 

Above a certain concentration, however, all the active sites are occupied, and the reaction becomes zeroth order in the substrate. In other words, the rate remains the same even though the substrate concentration increases. At and beyond this point, the rate of formation of product depends only on how fast the ES intermediate breaks down, not on the number of substrate molecules present. 

Sucrase is an enzyme that catalyzes the breaking up of sucrose (table sugar) into glucose and fructose within the body. At body temperature, sucrose does not break into glucose and fructose because the activation energy is high, resulting in a slow reaction rate. However, 

The strategies used to speed up chemical reactions in the lahoratory-high temperatures, high pressures, strongly acidic or alkaline conditions-are not available to living organisms, since they would be fatal to cells. 

Glucose part Fructose part of molecule of molecule 

Sucrose breaks up into glucose and fructose during digestion. 

M FIGURE 13.21 En e-Substrate Binding A substrate (or reactant) fits into the active site of an enzyme much as a key fits into a lock. It is held in place by intermolecular forces and forms an enzyme-substrate complex. (Sometimes temporary covalent bonding may also be involved.) After the reaction occurs, the products are released from the active site. 

Figu re 14.19 Comparison of (a) an uncatalyzed reaction and (b) the same reaction catalyzed by an enzyme. The plot in (b) assumes that the catalyzed reaction has a two-step mechanism, in 

All active sites are occupied at and beyond this substrate concentration. 

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Ethanol is also produced by the fermentation of sugars such as glucose. The reaction is carried out at about 35°C in the presence of yeast, which contains an enzyme (biological catalyst) called zymase. 

Enzyme biological catalysts proteins that can accelerate chemical reactions without being changed themselves. Most enzymatic reactions occur within a narrow temperature range, from 30 to 40°C. Most enzymes react with only a small number of closely related compounds, and some require the presence of additional small non-protein molecules (coenzymes). 

Mitochondria contain deoxyribonucleic acid (DNA) and ribosomes, protein-producing organelles in the cytoplasm. The DNA directs the ribosomes to produce proteins as enzymes (biological catalysts) in ATP production. 

Enzymes Biological catalysts whose role is to increase the rate of chemical (metabolic) reactions without being consumed in the reaction. 

All the substances that cause these unpleasant and possibly lethal effects are chemicals, albeit manufactured by a plant, micro-organism, or animal. They may be simple irritant chemicals such as the formic acid in ant bites (formica is the Latin for ant), or complex protein molecules such as is found in bee venom. Proteins are relatively large molecules, one of the main building blocks of the body and also the main component of enzymes (biological catalysts). The venom of animals such as snakes often contains enzymes which degrade flesh. Mushrooms and toadstools are another source of poisonous chemicals, for example the Death Cap mushroom found in Britain which can be lethal if eaten. 

A catalyst is a substance that speeds up a reaction without being consumed itself. Just as virtually all vital biological reactions are assisted by enzymes (biological catalysts), almost all industrial processes also benefit from the use of catalysts. For example, the production of sulfuric acid uses vana-dium(V) oxide, and the Haber process uses a mixture of iron and iron oxide. 

Biological processes are highly sophisticated but are not driven by unknown and mysterious powers. They occur due to complicated combinations of known chemical reactions. These chemical reactions are conducted by enzymes (biological catalysts), which encourage desirable reactions to occur with high selectivity and efficiency. The application of naturally occurring enzymes to... 

This reaction is catalyzed by the enzymes (biological catalysts) found in yeast, and it can proceed only until the alcohol content reaches approximately 13%, at which point the yeast can no longer survive. Beverages with higher alcohol content are made by distilling the fermentation mixture. 

Proteins function as enzymes (biological catalysts), antibodies, messengers, carriers, receptors, structural units, etc. Their chemical structure and molecular conformation are commonly described in terms of ... 

Enzymes Biological catalysts made of proteins. Fermentation Metabolic reaction that is necessary to generate energy in microbial cells used to produce many important compounds, such as alcohol and acetone. 

Enzyme Biological catalyst, usually a globular protein. 

Another set of significant photochemical reactions in human biochemistry is contained in the chemistry of vision. These reactions involve vitamin A (retinol), which is a C20 compound belonging to a class of compounds known as diterpenes. These compounds are molecules formally constructed by the biopolymerization of four isoprene, CH2=C(CH3)—CH=CH2, molecules. Retinol (an all-trans pentaene) is first oxidized via liver enzymes (biological catalysts) to vitamin A aldehyde (frans-retinal). The frans-retinal, which is present in the light-sensitive cells (the retina) of the eye, undergoes further enzymatic transformation (retinal isomerase) to give cfs-retinal (a second form of vitamin A aldehyde) in which one of the double bonds of the aU-trans compound is isomerized. 

Heterogeneous Catalysis Homogeneous Catalysis Enzymes Biological Catalysts... 

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