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Biochemistry Enzymes
Chapter 11
| Question | Answer |
|---|---|
| Enzymes are better than chemical catalysts by what factors? | Higher reaction rates. (Catalysis orders of magnitude better.) Milder reactions conditions. (Work at physiological pH and temperature.) Greater reaction specificity. Both in terms of reactants and products, including their stereo-chemistries. Regulate |
| What are the six classes of enzymes? | 1. Oxidoreductases- Oxidation- reduction reactions 2.Transferases- transfer of functional groups 3. Hydrolases- Hydrolysis reactions 4. Lysases- group elimination to form double bonds. 5. Isomerases- Isomerization 6. Ligases- bond formation coupled ATP |
| What are cofactors? | May be metal ions or organic molecules that provide chemical groups and/or reactivities not available among amino acid R groups. |
| What are organic cofactors termed? | Coenzymes |
| What are prosthetic groups? | Coenzymes that are permanently bound. |
| What are cosubstrates? | Coenzymes that are not permanently bound. |
| How does confining substrates and catalytic groups in close proximity affect the rate of reaction? | It increases the frequency of collisions increasing the reaction rate alone by a factor of five. |
| How does optimally orienting substrates and catalytic groups affect the reaction rate? | It increases the frequency of productive collisions and thus increases the reaction rate by a factor of ten. |
| How does preferential transition state binding affect the rate of a reaction? | The transition state forms more electrostatic and VDW interactions with the enzyme than the substrate(s) do. The resulting favorable chance in energy enthalpy in this case lowers the transition state free energy barrier. |
| In minimal enzyme-catalyzed reaction mechanism, steady state region is? | A reaction time course when the [ES] is relatively constant, so the reaction velocity is approximately linear. |
| In minimal enzyme-catalyzed reaction mechanism, the initial steady state region is? | Its where in vitro measurements of enzyme reaction velocities usually are made. This minimizes substrate consumption and product accumulation. |
| What is (k) rate constant? | For a first order process, the rate is concentration independent and has units of 1/time. So min-1 or s-1. Measured number of substrates per minute. |
| What is the rate constant for second order process? | The second order process has units of 1/concentration x time. This is because the frequency at which E and S collide and form ES depend upon their concentrations. |
| What is the Michaelis Menten equation? | It defines the relationship between the observed reaction velocity (vo) and [S]. The equation is vo= Vmax[S} / Km+[S] |
| What is Vmax? | Vmax = kcat [E] total whereas kcat is the maximum number of substrate molecules that can be turned over by one enzyme molecule per unit of time. |
| What is kcat/Km? | It is a measure of enzyme efficiency, if how close it is to the maximum. |
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