Term
| Explain the propeties of a catalyst: |
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Definition
1) Increases the rate of a reaction, 2) Is not itself changed at the end of the reaction, 3) Does not change the nature of the reaction or its final result. |
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Term
| How do enzymes function as catalysts? |
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Definition
| They increase the rate of chemical reactions at lower temperatures by lowering the activation energy required. This ensures that a larger percentage of the poulation of reactant molecules will have sufficient energy to participate in a reaction. |
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Term
| How can a reaction occur without an enzyme? |
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Definition
| A small fraction of the reactants will have the activation energy required for a reaction, but it would occur at a rate much too slow for the needs of a cell. A higher temerature would make a reaction go faster, but it would produce undesirable effects on the cell. |
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Term
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Definition
| They end in "ase" (except for some older enzyme names, such as pepsin) and they are named according to their activity or "job category". Many enzymes also specify both the substrate and job category. |
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Term
| Use the lock-and-key model to explain how enzymes function as catalysts: |
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Definition
Substrates "A" and "B" fit into specific active sites in the enzyme. This forms an enzyme-substrate complex. This complex then dissociates, releasing the products of the reaction (which are changed) and the free enzyme (which is unchanged). (reactants) ---> (products) A + B C + D |
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Term
| Expalin the nature of isoenzymes: |
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Definition
| Enzymes that do exactly the same job (that catalyze the same reaction) in different organs have the same name. However, sometimes different organs might make different "models" of the enzyme, that differ by a few amino acids (isoenzymes). The difference in structure do not affect the active sites (or it wouldn't catalyze the same reaction) but they alter the structure of the enzymes at other locations, so the different isoenzymatic forms can be specialized by standard biochemical procedures. |
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Term
| Describe the effects of temperature on enzyme catalyzed reactions: |
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Definition
| At 0oC the reaction is immesurably slow, and as the temperature increases the rate of the reaction increases, but only to a cartain point. A few degrees above 37oC it plateaus, and above that it decreases the rate of the reaction. |
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Term
| Describe the effects of pH on enzyme-catalyzed reactions: |
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Definition
| Each enzyme characteristically exhibits peak activity in a very narrow pH range-- which is the pH optimum for that enzyme. If the pH is changed so that it is no longer in the opitimal range, the reaction rate will decrease. The pH optimum of an enzyme usually reflects the pH of the body fluid in which the enzyme is found. |
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Term
| Describe the nature of cofactors: |
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Definition
| Some enzymes require ions that play an essential role in enzyme activity. Cofactors include metal ions such as Ca2+ and Mg2+. In these enzymes that attachment of cofactors cause a conformational change in the protein that allows it to combine with its substrate. |
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Term
| Describe the nature of coenzymes: |
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Definition
| Coenzymes are organic molecules derived from water soluble vitamins such as niacin and riboflavin, which are needed for the function of particular enzymes. they participate in enzyme-catalyzed reactions by transporting hydrogen atoms and small molecules from one enzyme to another. |
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Term
| Explain the law of mass action in reversible reactions: |
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Definition
It is the principle that reversible reactions will be driven to the side of the equation where the concentration of substrates are higher to the side where the concentration is lower. ex. H2CO3--->H2O + CO2 and H2O + CO2--->H2CO3 are the same as H2CO3<---->H2O + CO2 |
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Term
| Describe a metabolic pathway: |
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Definition
| It is a sequence of enzymatic reactions that begins with an initial substrate, progresses through a number of intermediates and ends with a final product. ex. An assembly line where each worker contributes a small part to the final product. Most metabolic pathways are branched so that one intermediate at a branch point can serve as a substrate for two different enzymes. |
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Term
| Describe how a metabolic pathway is affected by end-product inhibition: |
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Definition
| It is a form of negative feedback. One of the final products of a divergent pathway inhibits the activity of the branch-point enzyme that began the path toward the production of this inhibitor. This prevents the final product from accumulating excessively and results in a shift toward the final product of the alternate pathway. |
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Term
| Describe how a metabolic pathway is affected by inborn errors of metabolism: |
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Definition
| It is an inherited defect in a gene that codes for an enzyme protein participating in a metabolic pathway. The quantity of the intermediates prior to the defective enzymatic step increases, and the quantity of intermediates and final products after the defective step decreases. |
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Term
| Draw a graph representing the effects of changes in temperature on the rate of enzymatic reactions: |
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Definition
| Enzymes work in narrow ranges of temperature. It reaches a peak performance at body temperature, plateaus, and decreases after temperature increases above normal body temperature ranges. This is because its tertiary structure is altered at high temepratures. |
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Term
| Draw a graph representing the effects of changes in pH on the rate of enzymatic reactions: |
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Definition
| Enzymes work in the pH optimum for the specific enzyme. If pH is changed to where it is no longer in that range, its reaction rate decreases. |
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Term
| Draw a graph representing the effects of changes in substrate concentration on the rate of enzymatic reactions: |
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Definition
| The rate of product formation will increase as substrate concentration increases. When the relationship between substrate concentration and reaction rate reaches a plateau of maximum velocity, it is said to be saturated. |
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Term
| Using arrow and letters of the alphabet, draw a flowchart of a metabolic pathway with one branch point: |
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Definition
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Term
| Describe a reversible reaction: |
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Definition
It is when both the forward and backward reactions are catalyzed by the same enzyme. The direction of the reversible reaction depends, in part, on the relative concentrations of molecules to the left and right of the arrows in the equation. ex. If CO2 is very concentrated (as in tissues) the reaction would be driven to the right. If the concentration of CO2 is low (as in lungs) it would be driven to the left. ex. H2CO3---> H20 + CO2 and H2O + CO2---> H2CO3 = H2O + CO2<---> H2CO3 |
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Term
| Define allosteric inhibition: |
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Definition
| It is the mechanism by which a final product in a metabolic pathway inhibits an earlier enzymatic step during the process of end-product inhibition. The allosteric inhibitor combines with a part of the enzyme at a location other than the active site. This causes the active site to change shape so that it can no longer combine properly with its substrate. |
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Term
| Use the diagram of a branched metabolic pathway to show how end-product inhibition will affect the concentration of different intermediates. |
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Definition
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Term
| Beacause of an inborn error of metabolism, suppose the enzyme catalyzed in the 3rd reaction of a simple branched metabolic pathway was defective. Describe the effects this would have on the concentrations of the intermediates in the pathway: |
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Definition
| The quantity of intermediates before enzyme 3 would increase, and after enzyme 3 the quantity of intermediates would decrease. Since it occurs at a point following the branch point in the pathway, the intermediates and final products of the alternate pathway will increase. The lack of intermediates and a final product in the defective branch can cause disease, and the increase of intermediates and final product in the alternate pathway can cause disease. |
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Term
| Distinguish between endergonic and exergonic reactions: |
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Definition
1) Endergonic- Chemical reaction that requires an input of energy. Products must contain more free energy than the reactants, and a portion of the energy added is contained within the product molecules. 2) Exergonic- Chemical reaction that converts molecules with more free energy to molecules with less. This releases energy. |
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Term
| How does ATP function as a universal energy carrier? |
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Definition
| The formation of ATP is a coupled reaction, meaning that the energy released (exergonic) by ATP into ADP fuels the endergonic reaction needed to form ADP into ATP, and power all the energy-requiring processes of the cell. This relationship is like two meshed gears. ATP release liberates energy (and some is lost) which turns the gear. This turns the other, energy-requiring gear, needed to keep the cell alive-- this keeps the energy going. |
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Term
| Distinguish between oxidation and reduction reactions: |
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Definition
| Oxidation is when a molecule donates electrons or hydrogens, and reduction is when a molecule gains electrons or hydrogens. An oxidation-reduction reaction is when electrons are transferred from the reducing agent (which becomes oxidized) to the oxidizing agent (which becomes reduced). |
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Term
| Explain the functions of NAD+ and FAD: |
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Definition
| NAD+ and FAD are coenzymes that function as hydrogen carriers because they accept hydrogens (becoming reduced) in one reaction and donate hydrogens (becoming oxidized) in another reaction. Each FAD can accept 2 electrons and bind 2 protons, so the reduced form of FAD is FADH2. Each NAD+ can also accept 2 electrons, but can only bind 1 proton, so the reduced form of NAD+ is NADH+H. When the reduced form of these two coenzymes participate in an oxidation-reduction reaction, they transfer 2 H atoms to the oxidizing agent. |
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Term
| Describe the first law of thermodynamics: |
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Definition
| Energy can neither be created nor destroyed , but only transferred from one atom to another. |
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Term
| Describe the second law of thermodynamics: |
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Definition
| All energy transformation reactions result in an increase in entropy (disorder). This results in a decrease in usable (free) energy. Atoms organized into large organic molecules thus contain more free energy than more disorganized, smaller molecules. |
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Term
| Use the first and second laws of thermodynamics to explain why the chemical bonds in glucose represent a source of potential energy: |
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Definition
| The combustion of glucose to CO2 and H2O releases chemical bond energy. The energy is not created nor destroyed, the molecules are just rearranged and energy is released. Since the transformation reaction caused an increase in entropy, there was a decrease in useable energy, which is lost as heat. |
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Term
| How can cells obtain the energy from the combustion of glucose? |
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Definition
| The breakdown of food molecules (glucose) converts into CO2 and H2O. This is an exergonic reation, releasing energy-- which is coupled to an endergonic reaction to form ATP. The breakdown of ATP into ADP and Pi releases energy, and this released energy powers all the energy-requiring processes of the cell. |
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Term
| Using the symbols X-H2 and Y, draw a coupled oxidation-reduction reaction. Designate the molecule that is reduced and the one that is oxidized and state which one is the reducing agent and which is the oxidizing agent. |
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Definition
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Term
| Describe the functions of NAD+, FAD and oxygen (in terms of oxidation-reduction reactions): |
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Definition
| 1) NAD+ and FAD can become reduced by accepting electrons from hydrogen atoms removed from other molecules. 2) NADH+H and FADH2 in turn, donate these electrons to other molecules in other locations within the cells. 3) Oxygen is the final electron acceptor (oxidizing afent) in a chain of oxidation-reduction reactions that provide energy for ATP production. |
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Term
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Definition
| Nicotinamide adenine dinucleotide; derived from niacin; they are coenzymes that function as hydrogen carriers, because they accept hydrogens (becoming reduced) in one enzyme reaction and donate hydrogens (becoming oxidized) in a different enzyme reaction. NAD is the oxidized form of the reaction. |
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Term
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Definition
| Flavin adenine dinucleotide; derived from riboflavin; they are coenzymes that function as hydrogen carriers, because they accept hydrogens (becoming reduced) in one enzyme reaction and donate hydrogens (becoming oxidized) in a different enzyme reaction. FAD is the oxidized form of the reaction. |
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Term
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Definition
| It is the reduced form of NAD+ (after it has accepted 2 electrons). It can only bind 1 proton, unlike FAD, which can bind 2 protons. The H+ in NADH+H+ represents a free proton. NADH+H is a reducing agent, meaning it becomes oxidized. |
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Term
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Definition
| It is the reduced form of FAD (after it has accepted 2 electrons). It can bind 2 protons, unlike NAD+, which can only bind 1 proton. FADH2 is a reducing agent, meaning it becomes oxidized. |
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