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Assessment 1.2
Amino Acids and Peptides
| Question | Answer |
|---|---|
| Reactant-Product | [A]+[B]----[C]+[D]-2nd order |
| [S]-----[P]- 1st order | |
| Substrate | reactant |
| Equilibrium Constant | Keq=[C]x[D]/[A]x[B] |
| Keq= [P]/[S] | |
| Equilibrium | constant amount of substrate |
| Molarity | Avogadro's Number- 6.02 x 10^23 mol |
| Thermodynamics | moving forward equilibrium constant > 1 |
| moving backwards (reverse) equilibrium constant < 1 | |
| ^G`= -RTIn(Keq) | R= Universal Gas Constant T= Temperature in Kelvin In(x)=2.303 log(x) |
| Keq > 1= - G | tendency to move forward |
| Keq < 1= G | tendency to move in reverse (backwards) |
| - G | Don't know how long it'll take to occur, all we know is that it'll go forward |
| Enzymes | change the rate that the reaction is occuring by lowering the Gact |
| globular proteins (soluble) | |
| Globular | highly folded proteins, water soluble |
| Fibrous | elongated proteins, insoluble |
| Catalyst | reduce the activation energy of reactions |
| All reactions have a activation energy called catalyst | |
| Cofactor | a small (relative to protein) molecule required for enzyme activity. May be organic or inorganice, tightly bound or loose |
| Coenzyme | an organic factor that is loosely bound to the enzyme, like a substrate |
| examples: NADP(H),NAD(H), ATP | |
| apoprotein | the folded polypeptide chain of conjugated protein |
| holoprotein | the complete, biologically active protein conjugate, consisting of the folded polypeptide chain(s) and any relevant cofactors, a apoprotein combined with its prosthetic group |
| Effect of pH and temperature on Enzyme | as temperature increases the kinetic energy of the molecules increase, including that of substrate molecules |
| Too high of temp will denature the proteins | |
| Lipase | group of enzymes named after the activator |
| Active Sites | the region of the enzymes that binds the substrate |
| substrates are bound by noncovalent bonds | |
| If you change the active site on the amino acid it creates a big problem | |
| Lock and Key Concept | |
| Antibody can bind two of the same antigen | |
| Enzyme has 5 active sites and only 2 substrates bond to the enzyme it is considered to be unsaturated | |
| The enzymes are completely (filled) bonded to all active sites this is considered to be saturated | |
| Enzymes can have more than one active site | |
| Structural Mechanisms account for an enzyme's ability to reduct Gact | Entropy Reduction, General Acid-Base Catalysis, and Covalen Catalysis |
| Entropy Reduction | one or more substrates bind in active site with the correct orientation for reaction; randomness |
| The enzyme has to have a binding site | |
| General Acid-Base Catalysis | Substrate protons important for reactivity are accepted or donated by the amino acid in the active site |
| Accounts for the pH-dependence of enzyme activity. | |
| Covalent Catalysis | A transient covalent bond is formed between the enzyme and substrate-usally for cleavage. Makes uses of kinases. |
| Six Classes of Enzyme Reactions | |
| 1. Oxidoreductase | Catalyze oxidation/reduction reactions, transfer of electrons from one compound to another, thus changing the oxidation state of both substrates |
| Dehydrogenases- transfer of H- | |
| Oxygenases- Oxidizes with O2 | |
| Peroxidases- (i.e. catalase) | |
| Phosphoralated- turning reaction on and off | |
| Alcohol dehydrogenases occurs in the liver and breaks down alcohol | |
| Formealdehyde- Formic Acid Example | |
| 2. Transferase | Catalyze reactions in which a functional group is transferred from one compound to another. ex-kinases |
| kinases- adds a phosphate to protein, transfers to group with hydroxyl group(serine,tyrosine, & threonine) | |
| AST-aspartate transaminase ALT- alanine transaminase Get these two reading from the blood analysis to find out the condition of the liver. | |
| AST & ALT levels are both high if taking in too much APAP, excessive alcohol consumption which causes liver damage. | |
| If both levels are high then something is going on with the liver. If AST level is high and ALT is normal then something else is going on within the body besides the liver. | |
| 3. Hydrolases | cleave bonds by adding water across the bond |
| 4. Lysases | cleaves bonds but do so without addition of water |
| 5. Isomerases | no change of molecule, creating isomers by moving functional groups |
| 6. Ligases/Synthetases | catalyze formation of new chemical bond by coupling their formation of the cleave of a high energy compound. |
| Ligases differ from lyases in that they utilize the energy obtained from cleavage of a high energy bond to drive the reaction usually ATP. | |
| Isoenzymes | enzymes that catalyze the same reaction but differ in structure or sequence |
| Mechanisms of Enzyme Regulation | |
| 1. Product Inhibition | direct, reversible inhibition at an enzyme's active site by the product of the enzyme-catalyzed reaction. whats going to happen |
| single Step glucose-------- Glucose -6-phosphate | |
| 2. Allosteric Regulation | bind the enzyme at a location distinct from the active site and cause a conformational change in the protein |
| product inhibition- inhibits the same enzyme that produced the product | |
| feedback inhibition- often involves a molecule producted "Downstream" in the pathway acting as an inhibitor | |
| multi-step process A-B-C-D-E (product) | |
| 3.Covalent Modification or Phosphorylation regulation | protein kinase transfer phosphate from ATP to Serine, Tyrosine Threonine |
| Phosphorylation can increase of deacres the enzymes catalytic activity | |
| 4.Protein Protein Interaction | binding of an enzyme by another protein to form a complex can result in activation or inhibition of an enzyme |
| Calmodulin (EF hand, Ca2+ binding protein | |
| 5. Zymogen Cleavage | zymogen- inactive form on a enzyme that can be activated |
| digestive enzymes are often synthesized as zymogens, then activated by on demand by the other proteases | |
| proteases- protein cleaving enzymes | |
| Enzyme regulation involves proteins that are inactive inhibitors | |
| 6.Enzymes Synthesis and Degradation | Vmax is proportional to the amount of enzyme present |
| Increase Vmax add enzymes | |
| How to measure the reactant rate? Measure how fast the product is producing | |
| Increaseing the substrate the reaction rate will increase until saturation then it'll plateau (Vmax) | |
| Enzymology | Enzymes are markers for diseases. Damage cells release isozymes that are normally intracellular. |
| Creatine Phospho(kinase) CK is used to diagnose myocardial infarction. stored in the muscle | |
| CK-BB- outside the brain | |
| CK-MM-skeletal muscle and heart muscle | |
| CK-MB- mostly in the heart; increased levels indicates something is wrong with the heart (attack) | |
| CK and LDH are common enzymes used to diagnose myocardial infarctions. LDH 1 & 2 are the important ones | |
| Examples of Therapeutic Enzymes | |
| Tissue Plasminogen Activator | dissolves blood clots |
| Asparaginase | used in acute lymphoblasts leukemia |
| Lactase | lactose intolerant |
| Substrate Concentration | Km |
| doesn't effect velocity | |
| low Km- higher affinity of enzyme to the substrate | |
| Vmax | depends on the character of the enzyme and the substrate, and on the amount of the enzyme, when it plateaus out |
| more enzyme=higher Vmax less enzyme= lower Vmax | |
| adding more substrates not going to effect | |
| Km | appears as the substrate concentration at which the rate of catalysis in half Vmax |
| = 1/2 Vmax | |
| 1/2 is free and 1/2 is bound with substrates | |
| Kcat | is the turnover number (Vmax/total (E)) the enzyme's top speed |
| Kcat/Km | is a measure of an enzyme's catalytic efficiency bigger=better |
| Enzyme Inhibition | |
| 1. Reverse Competitive Inhibition | competitive inhibitor competes with the substrate for the active site of the free enzyme |
| lowers the effective product Vmax= stays the same, Km increases | |
| Example: Lipitor lowers serum cholesterol by reversibly and competitively inhibiting HMG-CoA reductase | |
| 2. Uncompetitive Inhibition | Binds to enzyme when substrate is also bound |
| Vmax=lowers Km=decreases | |
| Example: Mycophenolate (Cellcept) suppresses the immune system following an organ transplant | |
| 3. Mixed and Pure Noncompetitive Inhibition | binds free enzymes and enzyme substrate complex, but doesn't bind at the active sites |
| Vmax= lower Km=usually lower | |
| Km= can increase (like a competitive inhibitor) or decrease (like an uncompetitive inhibitor) | |
| Example: Caspofungin- used to treat yeast infections & Foscarnet- antiviral inhibits viral DNA polymerase and used to treat herpes virus | |
| 4. Irreversible Inhibition | poisons the enzyme by covalently modifying the active site of the free enzyme |
| permanent damage | |
| Vmax=lower Km=unchanged | |
| Example: Sarin Nerve Gas- irreversible acetylcholinesterase inhibitor; nerve damage causing muscle contraction, pulmonary arrest and death | |
| Lineweaver-Burk Plot | K0.5 used instead of Km |
| Allosteric inhibitor shifts the curve to the right (makes it more sigmoidal) and increases K0.5 | |
| Allosteric Activator- shifts the curve to the left (makes it more hyperbolic) and decrease K0.5 | |
| Competitive Inhibitor | line increasing with inhibitor (on graph) Km=increasing 1/v (Y intercept) stays the same |
| Uncompetitive Inhibitor | Y intercept-different Km=decrease Vmax & Km=decrease |
| Noncompetitive or Mixed Inhibition | Converge on X intercept. look at graphs! |
Created by:
lisagoette
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