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Enzymes.
| Question | Answer |
|---|---|
| Oxidoreductases | -catalyze redox reactions -involve NAD,NADP,FAD as electron acceptors or donors (reduced form) -oxidases, oxygenases, reductases, and dehydrogenases |
| Transferases | -transfer groups from one substrate to another -transfer carboxyl, amino, glucosyl, phosphoryl and methyl -kinases, aminotransferases, carboxylases, and methyltransferases |
| Hydrolases | -cleave bonds between atoms by addition of water -glucosidases, ATPases, phosphatases, peptidases and lipases |
| Lyases | -break bonds between atoms without addition of water or oxidative cleavage of substrate -usually break C-C bonds -often contain lyase in name |
| Isomerases | -change stereochemistry of optical or geometric isomers -mutases, epimerases or recemases |
| Ligases | -catalyze formation of bonds between carbon and other atoms -require input of energy from ATP or others -synthase, synthetase or carboxylase |
| Metalloenzymes | -metal containing enzymes -metal ions with positive charge plays important role in reaction mechanism of enzyme |
| Coenzymes | -cofactors that are small organic molecules -typically derived from vitamins -NAD, NADP, FAD -prosthetic group |
| Holoenzyme | -active enzyme with its prosthetic group attached -also used to describe multimeric enzymes consisting of several subunits |
| Apoenzyme | -inactive enzyme without its prosthetic group |
| Active sites of an enzyme | -small site where enzyme binds its substrate -often found in pocket or crevice without water |
| Induced fit model | -active sites are flexible -binding substrate produces conformational change at active site |
| Stereospecific reactions | - allow precise active site-substrate interactions without generation of unwanted byproducts -cannot assume R and S-enantiomers behave similarly -50% drugs are chiral |
| Acid-Base Catalysis | -ionizable R groups of active site serve as proton donor and acceptors -pKa of R groups tells functioning pH effective for proton donor/acceptor during catalytic cycle -no activity at extreme pH due to denaturation |
| Covalent Catalysis | -transient formation of covalent bond between substrate and active site R groups -unstable -breaks down to regenerate free enzyme |
| Metal Ion Catalysis | -+ charge stabilize negatively charged intermediates -generate nucleophile by increasing acidity of a nearby molecule (often water) -binds to substrate, increasing number of enzyme-substrate interactions |
| Effect of temperature on Enzymes and Rx rate | -increasing the temperature to a certain point can increase the rate of the reaction -when critical temperature is reached, interactions maintaining proper folding are overcome and denature the enzyme and catalytic activity is lost |
| Michaelis-Menten Equation | V=Vmax[S] / Km+[S] *Vmax=max velocity *S=substrate *Km=k2+k3 / k1 (M-M Constant) |
| Km | -[S] at which the reaction rate is half of its maximum value -value is independent of enzyme concentration -approximates dissociation constant of ES complex -low Km=tight binding -high Km=weak binding |
| Lineweaver-Burk plot | -takes reciprocal of both sides of Michaelis-Menten equation -gives straight line -x intercept= -reciprocal of Km -y intercept= reciprocal of Vmax -1/v=Km/Vmax x 1/[S] + 1/Vmax |
| Competitive Inhibitors | -competes with substrate for binding at active site -increase Km but not affect Vmax -more substrate will reduce inhibition |
| Non-Competitive Inhibitors | -bind to other sites than active site -[S] has no influence -Vmax decreased but no change in Km |
| Irreversible Inhibitors | -chemically modify and inactivate enzyme -bonds between enzyme and inhibitor are permanent -Asprin |
| How can you distinguish between noncompetitive and irreversible inhibitors? | -upon removing non-competitive inhibitors, full enzymatic activity can be restored, unlike irreversible inhibitors |
| Isozymes (Isoenzymes) | -Proteins that have different amino acid sequences, but catalyze same biochemical reaction -different isozymes are found in different tissues |
| Glucokinase and Hexokinase | -Isozymes that catalyze phosphorylation of glucose to generate glucose-6-phosphate -Km of hexokinase for glucose is 0.1mM -Km of glucokinase is 5mM -hexokinase has higher affinity for glucose |
| What is the clinical importance of LDH isozyme profiles? | -by determining the composition and amount of isozyme in the serum, MI's can be detected |
| What simple step can the body take to increase enzymatic Rx rate? | -make more enzyme |
| 3D structure of isozymes of prostaglandin synthase and drug selectivity | -bad prostaglandins synthesized at site where valine residue is present (not present at good proglandin site) -drugs can be made to selectively inhibit the bad site, but not the good site |
| Product Inhibition give an example | -inhibition by the products of the reaction catalyzed -phosphorylation of glucose (competition between product and substrate) |
| Allosteric modulators | -bind at sites distinct from active site -positive or negative |
| Regulatory subunits and how they differ | -inhibitory subunits=inhibit activity of catalytic subunit -activating subunits=sometime reuired for activation of catalytic activity, binding alters conformation -targeting subunits=direct them to their substrate |
| Addition and removal of phosphate | -most common way to regulate enzyme activity -binds to serine, threonine or tyrosine residue -bulky and charged, altering conformation of enzyme -protein kinases add Phosphate -protein phosphatases remove |
| Zymogens and Chemotrypsin activation | -enzyme synthesized in inactive state -activated by proteolysis -Chemotrypsin activated by trypsin to chemotrypsinogen -trypsin is also a zymogen, activated by enteropeptidase |
| Multienzyme complexes vs. multifunctional proteins | -Multienzyme complex= association of subunits (distinct enzymes) -Multifunctional protein=protein folded with multiple active sites and distinct catalytic activity |
| Why is the physical association of enzymes an advantage to the cell? | -eliminates substrate diffusion/dissociation between sequential enzymatic reactions -coordinated control of sequential enzymatic steps -coordinated, stoichiometric gene expression of enzyme activities |
| Effect of enzymes on: -activation energy <> -equilibrium constant -eq. concentrations of reactant and product -forward and reverse rate constants - | -activation energy is decreased in both directions -eq. concentrations of S and P is unaffected -rate constants are increased |
| Correlation between Km and metabolic concentration due to.. - | -representing an optimal balance in sensitivity to increase and decrease on [S] |
Created by:
MastamikeOD
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