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Flashcards in Enzymes Deck (90):
1

Protein catalysts that increase the velocity of a chemical reaction and are not consumed during the reaction they catalyze

Enzymes

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Physically distinct versions of a given enzyme, each of which catalyzes the same reaction

Isozymes

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Catalyze oxidations and reductions

Oxidoreductases

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Catalyze transfer of moieties such as glycosyl, methyl, or phosphoryl groups

Transferases

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Catalyze hydrolytic cleavage of C-C, C-O, C-N and other bonds

Hydrolases

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Catalyze cleavage of C-C, C-O, C-N and other bonds by atom elimination, leaving double bonds

Lyases

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Catalyze geometric or structural changes within a molecule

Isomerases

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Catalyze the joining together of two molecules coupled to the hydrolysis of ATP

Ligases

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Properties of Enzymes

Contain an active siteHighly efficientHighly specificRequire cofactorsCompartmentalizedCan be regulated or inhibited

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Distinguished by their tight, stable incorporation into protein's structure by covalent or noncovalent forces

Prosthetic Group

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Bind in transient, dissociable manner either to the enzyme or to a substrate

Cofactor

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Serve as recyclable shuttles or group transfer agents that transport many substrates from their point of generation to their point of utilization

Coenzyme

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How enzymes work?

Lower free energy of activationDo not change the energy of the reactants and products and the equilibrium of the reaction

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Describes how reaction velocity varies with substrate concentration

Michaelis-Menten Equation

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Enzymes that follow Michaelis-Menten Kinetics have a

Hyperbolic curve

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Allosteric reactions have

Sigmoid curve

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Low substrate affinity =

High Km

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High substrate affinity =

Low Km

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Factors that affect the reaction rate

Substrate concentrationTemperaturepH

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Zero Order KineticsRate not affected by substrate concentration

Above Km

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First Order KineticsRate directly proportional to substrate concentration

Below Km

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High Temperature =

Increased reaction rate

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Extremely High Temperature =

Decreased reaction rate (due to denaturation)

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pH Extremes =

Decreased reaction rate (due to denaturation)

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Reciprocal of the Michaelis-Menten Equation; Used to calculate Km and Vmax as well as to determine the mechanism of action of enzyme inhibitors

Lineweaver-Burk Plot

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Any substance that can diminish the velocity of an enzyme-catalyzed reaction

Enzyme inhibitor

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Inhibitor is shaped similar to substrate and competes for binding site; Increase substrate, Increased Km, Vmax Not changed

Competitive Inhibitor

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Inhibitor binds to enzyme somewhere other than the active site and halts catalysis; Increased enzyme, Km Not changed, Vmax Lowered

Noncompetitive Inhibitor

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Regulation of Enzyme Activity

Change in substrate concentrationThrough allosteric binding sitesThrough covalent modification of the enzymeThrough induction and repression of enzyme synthesis

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The substrate itself serves as an effector

Homotropic Effectors

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The effector is different from the substrate

Heterotropic Effectors

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Serum Enzyme: Aspartate aminotransferase

Myocardial infarction

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Serum Enzyme: Alanine aminotransferase

Viral hepatitis

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Serum Enzyme: Amylase

Acute pancreatitis

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Serum Enzyme: Ceruloplasmin

Hepatolenticular degeneration (Wilson's disease)

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Serum Enzyme: Creatine kinase

Muscle disorders and Myocardial infarction

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Serum Enzyme: Gamma-Glutamyl transpeptidase

Various liver diseases

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Serum Enzyme: Lactate dehydrogenase (isozymes)

Myocardial infarction

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Serum Enzyme: Lipase

Acute pancreatitis

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Serum Enzyme: Phosphatase, acid

Metastatic carcinoma of the prostate

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Serum Enzyme: Phosphatase, alkaline (isozymes)

Various bone disorders, obstructive liver diseases

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Transfer and utilization of energy in biologic systems

Bioenergetics

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Measure of heat content of the reactants and products; Measure in joules

Enthalpy (

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Measure of the change in randomness or disorder of the reactants and products; Measured in joules/Kelvin

Entrophy (

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Amount of energy that can be used;

Change in Free Energy (

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(-) Enthalpy (+) Entropy =

Always Spontaneous Reaction

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(+) Enthalpy (-) Entropy =

Always No Spontaneous Reaction

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(+) Enthalpy (+) Entropy =

Maybe Spontaneous Reaction, but only at High Temp

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(-) Enthalpy (-) Entropy =

Maybe Spontaneous Reaction, but only at Low Temp

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Adenosine molecule to which three phosphate groups are attached; Acts as the "energy currency" of the cell, transferring free energy derived from substances of higher energy potential to those of lower energy potential

Adenosine Triphosphate

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Any

Used to make ATP

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Any

Made from ATP

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How ATP is produced?

Phosphate transferOxidative phosphorylation

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Sources of High Energy Phosphorylation

Oxidative PhosphorylationSubstrate Level Phosphorylation

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Aerobic; The greatest quantitative source of high energy phosphate in aerobic organisms; Free energy comes from successive oxidation of substances in the respiratory chain within mitochondria; Molecular oxygen is the final substance to be reduced

Oxidative Phosphorylation

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Anaerobic; Done through coupling reactions where a phosphate group is transferred to ADP from another substance with higher

Substrate Level Phosphorylation

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In Glycolysis: ATP is generated in 2 steps

1,3-BPG + ADP ➡️3-PG + ATP (phosphoglycerate kinase)PEP + ADP ➡️pyruvate + ATP (pyruvate kinase)

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In Citric Acid Cycle: ATP is generated in 1 step

Succinyl CoA + ADP➡️succinate + ATP (succinyl thiokinase)

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Final common pathway by which electrons from different fuels of the body flow to oxygen; Occurs in inner mitochondrial membrane

Electron Transport Chain

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2 electron carriers used in ETC:

Nicotinamide Adenine Dinucleotide (NAD+) - from Vit. B3 (Niacin)Flavin Adenine Dinucleotide (FAD) - from Vit. B2 (Riboflavin)

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Parts of ETC: Complex I

NADH dehydrogenase

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Parts of ETC: Complex II

Succinate dehydrogenase (actually part of Krebs Cycle)

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Parts of ETC: Coenzyme Q

A lipid, aka UbiquinoneOnly non-protein part of ETC

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Parts of ETC: Complex III

Cytochrome b/c1 (Fe/heme protein)

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Parts of ETC: Cytochrome C

Fe/Heme protein, mobile part of ETC

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Parts of ETC: Complex IV

Cytochrome a/a3 (Cu/heme protein) aka Cytochrome oxidase

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What you have to remember about ETC?

1) Protons (H+) are pumped to the intermembranous space to create a gradient in 3 complexes: Complex I-NADH and flavoprotein, Complex III-Cytochrome B & C, Cytochrome IV-Cytochrome C & a+a32) All components are fixed to the inner mitochondrial membrane EXCEPT Coenzyme Q/Ubiquinone, Cytochrome C3) Final electron acceptor is Oxygen

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From oxidation of components in the respiratory chain is coupled to the translocation of Hydrogen ions (protons/H+); H+ moved from the inside to the outside of the inner mitochondrial membrane where it accumulates in the intermembranous space

Mitchell's Chemiosmotic Theory

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ETC generates an electrical gradient and a pH gradient across the inner mitochondrial membrane; Protons driven towards mitochondrial matrix; Results in the synthesis of ATP

Oxidative Phosphorylation

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2 components of ATP synthase

F1 - generates ATP from ADP + PiF2 - channel where protons pass through

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Deprives the ETC of sufficient oxygen, decreasing the rate of ETC and ATP production

Tissue Hypoxia

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Stops electron flow from substrate to oxygen

Inhibitors of ETC

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ETC Inhibitors: Complex I

BarbituratePiericidin AAmytalRotenone

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ETC Inhibitors: Complex II

MalonateCarboxinTTFA

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ETC Inhibitors: Complex III

Antimycin ADimercaprol

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ETC Inhibitors: Complex IV

CyanideCarbon monoxideSodium azideHydrogen sulfide

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Increase the permeability of the inner mitochondrial membrane to protons; Increased oxygen consumption; Increased oxidation of NADH; Decreased ATP synthesis

Uncouplers

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Examples of Synthetic Uncouplers

2,4 dinitrophenolAspirin

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Example of uncoupling proteins

Thermogenin

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Directly inhibits mitochondrial ATP Synthase (Complex V); Proton gradient continues to rise but there is no "escape valve" for the protons; ETC eventually stops because the cytochromes can no longer pump protons into the intermembranous space

ATP Synthase Inhibitors

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Example ATP Synthase Inhibitor

Oligomycin

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Reactive Oxygen Species

Superoxide (O2-)Hydrogen peroxide (H2O2)Hydroxyl radical (OH-)

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Unstable products that are formed as a by-product of ETC when molecular oxygen (O2) is partially reduced

Reactive Oxygen Species

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Mutation in the circular mitochondrial chromosome; Maternally inherited

Mitochondrial Diseases

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Mutation in the circular mitochondrial chromosome that encodes:

1) 13 proteins that comprise the major complexes of Oxidative Phosphorylation2) 22 tRNAs3) 2 rRNAs

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Examples of Mitochondrial Disease: All Complexes

Fatal Infantile Mitochondrial Myopathy

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Examples of Mitochondrial Disease: Complex I

MELAS (Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like episodes)

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Examples of Mitochondrial Disease: Complex II

Kearns-Sayre Syndrome

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Examples of Mitochondrial Disease: Complex III

Leber's Hereditary Optic Neuropathy

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Examples of Mitochondrial Disease: Complex IV

Leigh's DiseaseRagged Red Muscle Fiber Disease