Enzymes PDF

Enzymes  eeceeo eee@ eeeee0 ee Enzymes ® Enzymes are proteins that act as biological catalysts ® En...

Enzymes  eeceeo eee@ eeeee0 ee Enzymes ® Enzymes are proteins that act as biological catalysts ® Enzymes increase the rate of reactions without being changed. Substrate |_Joins ® Enzymes are selective and specific.  * The reactant in the biochemica l reaction is termed : seo substrate. ® The molecule the enzyme pr °°°° oduces is known asthe | ©= product. * The enzyme can be re-used Substrate * —— Fahne | a | | ‘Active site Enzyme The site on the enzyme = where the reaction occu =) The enzyme can be re-used % 3% Enzyme Classes 1. Oxidoreductases Catalyze oxidation-reduction react Ss. such as: CHs-CH- COO” + NAD* 2S CHs-C-COc” + NADH +H" i a os Lactate Lactate — Pyruvate i Containing Groups, such as: Catalyze H,0 transfer of C-, N-, or P- - — — CH2 —CH- COO” + THE CH COO” + THE Sernvrs fy On NH..* ernerrriye te cena ga NH.~ CH, Serine Glycine Catal cleavage of bonds =. yurotases by actdtion of water, such as: - NH.-C-NH HO co, + 2NH oo) ~ # i ha Urea — rae Catalyze cleava of C-c, CS 4. _yases and certain bonds, such as: CH3-Cc ; coo CHa-CH + COs Pyruvate © deca thoxpiase oO Pyruvate Acetaldehyde Catalyze racemization of 1 5. lsomerases or geometric isomers, ifs ages (*-9O0C-CHe-C-CoA re ena | Ha — —O0C-CHsCHs-C-CoA oO aiaba yy CoA oO MethyIimalony! CoA Ae Succiny! CoA : Catalyze formation of bonds 6. Ligases between carbon and ©, 5S, N — coupled to hydrolysis of high- _—————=-____ nergy phosphates, such as: —— ——— a. — —— ms, ~ CHsa-C- coo” + coe — “Oooc -CcH, -c- cool 3 o = rahe 2 oO capo ilase Pyruvate ATP aor +P, Oxaloacetate Nomenclature of enzymes ® Recommended name; Substrate-ase, e.g. urease, sucrase. * Systematic name; complete description of the chemical! reaction- ase, *® e.g. class: oxidoreductase, sub-class: dehydrogenase * Recommended or Accepted name: Lactate dehydrogenase * Systematic name: (lactate: NAD+ oxidoreductase). *® Chemical reaction: ; | Il = + NADt=—— = H,C—C—COOH + NAH] + Lactate Pyruvate Lactate Dehydrogenase L-Lactate:NAD Oxidoreductase =  eee eee eeoo0 Properties of Enzymes eee. ® 1. Protein catalysts. N.B. some RNA can act like enzymes and called ribozymes. 2. Increase velocity of reaction and arenotconsumed. Substrate cet Jae 3. Active sites | a y ss site /: oneness rN 4. Catalytic efficiency: Enzyme 10? to 10* times faster than uncatalyzed reactions. Turnover is the number of substrate molecules converted to product/enzyme molecule/second. Properties of Enzymes 5. Specificity: only one type of reaction. 6. Cofactors: are non-protein cofactors ® Metal ions, e.g. Zn, Fe, Mg, Mn ® Derivatives of vitamins known as coenzymes. ® Prosthetic group is tightly bound coenzyme and does not dissociate from BAZYOIS e.g. carboxylase and biotin. Permanently Associated Properties of Enzymes $3 6. Cofactors: ® Holoenzyme is Enzyme +co-factor. ® Apoenzyme is protein part of holoenzyme (not active). Apoenzyme + cofactor =— > Holoenzyme (inactive) (active) * Coenzymes determine specificity of reaction whereas substrates determine specificity of enzyme. Properties of Enzymes 7. Regulation: activated or inhibited. 8. Location within the cell: (compartmentalization) Many enzymes are localized in specific organelles within the cell. ?How Enzymes work ® The mechanism of enzyme action can be viewed from two different perspectives. ° The first treats catalysis in terms of energy changes. ° The second perspective describe how the active site chemically facilitates catalysis.  ovecececeo ,seeeeee ?How Enzymes work The mechanism of enzyme action can be viewed from two different perspectives. There is no difference in the free energy of the overall reaction (energy of reactants minus energy of products) 1. Energy changes occurring between the catalyzed and uncatalyzed during the reaction, free energy of activation is the energy difference between reactants and a high-energy intermediate that occur during the formation of product (Transition state). AT*B  eee eeen ?How Enzymes work ooo. eeoe eoo0 The mechanism of enzyme action can be viewed from two a different perspectives. 2. Chemistry of the active site Substrate Active » Site Active site facilitate the conversion of substrate to product. ‘Factors Affecting Reaction Velocity: 1) Substrate concentration ® Hyperbolic shape: Most enzymes show Michaelis-Menten kinetics. © Sigmoidal curve: Enzymes following Michaelis-| Allosteric enzymes. Menten kinetics hyperbolic curve. show —— ee ee ee eS eS eS SS eS oe — = Allosteric enzymes show sigmoid curve. | ae ee ee eee: ei” ee  Soe eee ‘Factors Affecting Reaction Veloci cy: eee The Effects of Substrate Concentration on Reaction Rate S = substrate S I ; P P== product prod E = enzyme 107 | Uncatalyzed 7 es ‘Reaction Ata fixed concentration of velocity enzyme, the velocity reaches a maximum 0 10 20 x 4) oO 60 70 80 90 100 [S] — [Substrate]  eee. eeen The Effects of Enzyme Concentration on Reaction Rate. aecece eee ee A. * Vmax is directly proportional 12 to enzyme concentration * The more enzymes present, the Pe a SSS RSE SESS SEER RSE eee faster the reaction. Enzyme concentration as before velocity velocity IV 47 Enzyme at half previous VP (=2.5) concentration 2+ Km (=4) 0 1 20 30 40 so 60 70 ao a0 1a) Enzyme|E}] Factors affecting reaction velocity *:° 2) Temperature Increasing velocity Denaturatior Factors affecting reaction velocity 3) PH Reaction velocity (v) Pepsin Trypsin Alkaline —=  Michaelis-Menten kinetics ® Enzymatic reaction * S binds reversibly to E to form ES complex. * ES complex then reacts irreversibly to generate a P and to regenerate the free E. fe Je flee E+S