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Lecture 6 for students of medical faculty Kinetics of Biochemical Processes

Kharkov National Medical University Department of Medical and Bioorganic Chemistry. Lecture 6 for students of medical faculty Kinetics of Biochemical Processes. Theoretical questions. Main concepts of chemical kinetics Correlation of the chemical reaction rate and the concentration

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Lecture 6 for students of medical faculty Kinetics of Biochemical Processes

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  1. Kharkov National Medical University Departmentof Medical and Bioorganic Chemistry Lecture 6for students of medical facultyKinetics of Biochemical Processes

  2. Theoretical questions • Main concepts of chemical kinetics • Correlation of the chemical reaction rate and the concentration • Correlation of the reaction rate and the temperature • Influence of chemical bond nature on the transformation rate • Catalysts and their mechanism of action • Chemical equilibrium

  3. Chemicalkinetics Chemical reaction Molecularity of a reaction Order of a reaction Rate of chemical reaction the presence of phases Factors influence the rate of a reaction

  4. Chemical reaction rate

  5. Concentration The concentration effect is described by the law of acting masses, formulated in 1867 by Norwegians K. Gulberg and P.Vaage: at a constant temperature the rate of the chemical reaction at each moment is directly proportional to the concentration of the reacting substances.

  6. The reaction molecularity The number of molecules which react simultaneously at the moment of collision accomplishing the act of chemical interaction is called the reaction molecularity. Сl22Сl-– monomolecular Н2 + І2 2НІ – bimolecular NO + NO+ O2 2NO2 – trimolecular The exponents of power in a kinetic equation are determined using special methods, they are called reaction order for the respective substance. General order of the reaction equals the sum of power exponents in the equation of chemical reaction rate. It should be noted that the notion of order and molecularity do not always coincide

  7. First-order reactions First-order reactions are characterized by a liner dependence of concentration logarithm on the time • The equation of kinetics of the rate of a first-order reaction has the following differential expression: =-dc/d=k1C • Half transformation time for first-order reactions is: 1/2=0,69/k1

  8. Second order reactions • The equation of dependence of concentration on the time for second-order reactions are considered only for the simplest cases, when the concentrations of reacting substances are equal: =-dc/d=k2C2 • Half-transformation time for second order reactions is: 1/2=1/(k2·С0) Linear dependence for second-order reactions with equal initial concentrations of the reacting substances is observed for the value of reverse concentration on time

  9. Zero-order reactions

  10. Dependence of the reaction rate on the temperature In 1879 Vant-Goff formulated an empirical rule: with temperature elevation by 10 degrees the rate of the chemical reaction increases 2-4 times: where  – temperature coefficient showing how many times the rate increases at temperature elevation by 10 degrees.

  11. Dependence of reaction rate on the nature of reactants Activation energy (Ea) is an abundant (when compared with the mean molecule energy) energy necessary for the substances to react on collision. Usually Ea is from 40 to 120 kJ/mol. The higher is Ea value, the lower is chemical reaction rate.

  12. Catalysis and catalysts A catalyst is a substance which alters the rate of a chemical reaction without being consumed in the reaction. The phenomenon of the change in the rate of a reaction under the action of catalysts is known as catalysis.

  13. Enzyme catalysis All biochemical reactions both in one-cell and higher organisms are catalytic. The role of catalysts is played by enzymes. • Simple ones have only a protein structure, • compound ones have non-protein components in addition to protein ones. The former are called prostetic groups or co-enzymes.

  14. The important characteristics of enzymes are: • High efficiency • Extremely small quantities. • Specificity. • Optimum temperature and pH. • Control of activity of enzymes.

  15. Leo Michaelis and Monica Mentenhave developed a general theory of enzymatic kinetics (1913). A quantitative relationship between the substrate concentration and the enzymatic reaction rate is: where km- Michaelis constant, which value depends on pH, temperature and the nature of the substrate. • at lower substrate concentrations the reaction proceeds as a first-order one ([S]<<Km): =(max/Km)·[S] • at higher substrate concentrations the reaction proceeds as a zero-order one: =max

  16. Thank you for your attention

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