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Chem- Enzymes
Chemistry SCC 10/2011
| Question | Answer |
|---|---|
| enzyme | a protein molecule that catalyzes chemical reactions without itself being destroyed or altered |
| catalyst | a substance that increases the rate of a chemical reaction but is not consumed or changed by it. |
| substrate | a substance upon which the enzyme acts |
| denaturation | the partial or total alteration of the structure of a protein without change in covalent structure by the action of certain physical procedures or chemical agents. Any disruption of the protein structure that is accompanied by a loss of activity |
| cofactor | nonprotein molecules that must bind to a particular enzyme before a reaction occurs (natural reactant – usually a metal ion or a coenzyme) |
| coenzyme | a diffusible, heat-stable substance of low molecular weight that when combined with an inactive protein called an apoenzyme forms an active compound or a complete enzyme called a holoenzyme |
| apoenzyme | the protein part of an enzyme |
| prostheticgroup | the coenzyme bound tightly to the enzyme |
| holoenzyme | the functional compound formed by the combination of an apoenzyme and its appropriate coenzyme |
| zymogen | Some enzymes, mostly digestive enzymes, are originally secreted from the organ of production in a structurally inactive form |
| activation energy | the energy required for a molecule to form an activated complex; in an enzyme-catalyzed reaction, corresponds to the formation of the activated enzyme substrate complex |
| enzyme-substrate complex (E-S) | a molecule of substrate is bound to the active center of the enzyme molecule |
| active site | where the initial binding of substrate and enzyme occurs |
| absolute specificity | meaning that the enzyme combines with only one substrate and catalyzes only the one corresponding reaction |
| group specificity | they combine with all substrates containing a particular chemical group |
| first-order kinetic reaction | a reaction in which the rate of reaction is proportional to the concentration of substrate |
| zero-order kinetic reaction | a reaction in which the rate is independent of the concentration of substrate, and depends on enzyme concentration only |
| activator | Inorganic cofactors, such as chloride or magnesium ions; They increase the catalytic activity of an enzyme when it binds to a specific site |
| inhibitor | interfere with the reaction, decrease the rate of reaction; can be either reversible or irreversible |
| uncompetitive inhibitor | binds to the enzyme-substrate complex so that increasing substrate concentration results in more ES complexes to which the inhibitor binds and thereby increases the inhibition so there is no product. |
| competitive inhibitor | binds to the active site of an enzyme and competes with substrate for the active site |
| noncompetitive inhibitor | binds an enzyme at a place other than the active site so no competition between inhibitor and substrate, examples are heavy-metal ions such as lead and mercury |
| Fixed time reaction | the amount of change produced by the enzyme is measured after the reaction is stopped (usually by inactivating the enzyme with a weak acid) at the end of a fixed time interval and a measurement is made of the amount of reaction that has occurred |
| continuous monitoring method | the reaction is monitored continuously, usually of absorbance change every 30 or 60 seconds. Continuous measurements are preferred because any deviation from linearity is readily observable |
| isoenzyme | one of a group of related enzymes catalyzine the same reaction but having different molecular structure and characterized by varying physical, biochemical, and immunological properties; subunit of the enzyme |
| NAD | nicotinamide adenine dinucleotide, example of a coenzyme |
| NADP | nicotinamide adenine dinucleotide phosphate, example of a coenzyme |
| Two-substrate reaction | more than one substrate yields more than one product and the concentrations of both substrates affect the rate of reaction |
| six classes of enzymes : | a. Oxidoreductases b. Transferases c. Hydrolases d. Lyases e. Isomerases |
| What are enzymes composed of | Proteins |
| What factors influence the actions of enzymes | - Substrate concentration - Enzyme concentration - Temperature - pH - activators - inhibitors |
| What unit of measurement (activity) is used to express enzyme concentration | International Unit -(U/L) Katal (mol/s) -Katals per liter (Kat/L). |
| How does temperature affect enzyme-catalyzed reactions? At what temperature are MOST enzyme catalyzed reactions performed? | optimal is 37°C; rate of an enzymatic reaction is proportional to its reaction temperature, until the temperature is high enough to denature the protein composition of the enzyme |
| At what pH are MOST enzymes optimally active? | Optimum pH is where the reaction rate is the fastest, must look at the pH activation curve for each enzymes optimum pH. |
| What enzymes and isoenzymes do we associate with the heart and MI's (myocardial infarction)? | CK, CK isoenzymes, LDH, LDH isoenzymes, AST, Troponin-I |
| What enzymes and isoenzymes do we associate with the liver and hepatic disease | AST, ALT, GGT, ALP, LDH (LDH-5), and 5’-NT |
| What enzyme and isoenzyme is associated with bone disorders? | ALP, ALP isoenzymes, ACP |
| Which enzymes are associated with pancreatic disease | AMS, LPS |
| Which enzyme is associated with prostate disease | ACP |
| Which enzymes and isoenzymes are associated with muscle disorders | CK, CK-MM, AWST, LDH (LD4 & LD5) |
| List the isoenzymes of CK and identify the tissue location of each. | CK-BB – brain CK-MM – skeletal muscle CK-MB – cardiac muscle (used in diagnosis of MI) |
| List the isoenzymes of LD/LDH and identify the tissue source of each. | LD-1 & LD-2 – cardiac muscle and RBCs LD-3 – lungs and spleen LD-4 & LD-5 – liver and skeletal muscle |
| What is the effect of hemolysis on MOST enzyme reaction tests | Falsely elevated results |
| What is the specimen of choice for most enzyme tests | Serum |
Created by:
CZUPAN
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