Enzymes Flashcards
What are protein catalysts that increase the velocity of a chemical reaction that are not consumed during the reaction they catalyze?
ENZYMES
What are enzymes?
Enzymes are protein catalysts that increase the velocity of a chemical reaction that are not consumed during the reaction they catalyse.
What are ISOENZYMES?
They are physically distinct versions of a given enzyme, each of which catalyses the same reaction.
What class of enzymes catalyse oxidations and reductions?
Oxidoreductases
What class of enzymes catalyse transfer of moieties such as glucose, methyl or phosphoryl groups?
Transferases
What class of enzymes catalyse hydrolytic cleavage of C-C, C-O, C-N and other bonds?
Hydrolases
What class of enzymes catalyse hydrolytic cleavage of C-C, C-O, C-N and other bonds by ATOME ELIMINATION, leading double bonds?
Lyases
What class of enzymes catalyse geometric or structural changes within a molecule?
Isomerases
What class of enzymes catalyse the joining together of 2 molecules coupled to the hydrolysis of ATP?
Ligases
What are physically distinct versions of a given enzyme, each of which catalyses the same reaction?
Isozymes
Theory that states that the active site of an enzyme fits the substrate like a key fitting into a lock?
Lock and Key Theory
Theory that states that the active site of an enzyme is slightly deformable to the shape of the substrate?
Induced Fit Theory
What is a holoenzyme?
apoenzyme + co-factor
“HOLOenzyme = the wHOLE thing”
What is an inactive enzyme without the cofactor?
apoenzyme
What is a complete enzyme with cofactor?
holoenzyme
What binds in a transient, dissociable manner either to the enzyme or the substrate?
co-factors
What is distinguished by their tight stable incorporation into a protein’s structure by covalent or non covalent means?
prosthetic group
What can bind multiple different types of enzymes and may bind some enzymes loosely, as a coenzyme, and others tightly, as a prosthetic group?
co-factors
Why are enzymes compartmentalised?
- for regulation of their function
- protection against inhibitors
- promote favorable compartment
Effect of enzymes on free energy of activation?
LOWERS the free energy of activation
Effect of enzymes on the energy of the reactants & products?
NO CHANGE
Effect of enzymes on the equilibrium of the reaction?
NO CHANGE
Differentiate Co-factors from Effectors?
Co-factors are required for function
Effectors are not required for function but they influence the rate of the reaction.
Differentiate Co-factors and Co-enzymes?
Co-factors are not proteins (ex. metal)
Co-enzymes are organic co-factors (ex. vitamins)
Are co-factors required for enzyme function? Co-enzymes?
BOTH are required for function
What describes how reaction velocity varies with substrate concentration?
The Michaelis-Menten Equation will describe how fast an enzyme will work at given substrate concentration.
What kind of curve will be seen with enzymes that follow Michaelis-Menten kinetics? Allosteric reactions?
MM kinetics: Hyperbolic curve (asymptote)
Allosteric rxns: Sigmoid curve
Vmax will not be plotted in a Michaelis-Menten equation because of what property? How can you then plot for Vmax?
Michaelis-Menten kinetics is an asymptote so use the LINEWEAVER-BURK PLOT
What component of the Michaelis-Menten equation will tell you how fast the reaction is?
Vi
What component of the Michaelis-Menten equation will tell you the maximum velocity?
Vmax
What component of the Michaelis-Menten equation will tell you the maximal number of substrate molecules converted to product per unit time?
Vmax
What component of the Michaelis-Menten equation will tell you the substrate concentration at which Vi is half the maximal velocity (Vmax/2) ?
Km or Michaelis constant
What is the Michaelis constant?
The Michaelis constant or Km is the substrate concentration at which Vi is half the maximal velocity (Vmax/2)
If an enzyme catalyses an equation with a low Km, what is its substrate affinity?
An enzymes that catalyses an equation with a low Km has a HIGH substrate affinity
If an enzyme catalyses an equation with a high Km, what is its substrate affinity?
An enzymes that catalyses an equation with a high Km has a LOW substrate affinity
If an enzyme has a high substrate affinity, what would be its expected michaelis constant (Km)?
LOW Km
If an enzyme has a low substrate affinity, what would be its expected michaelis constant (Km)?
HIGH Km
How does an enzyme lower the free energy of activation?
An enzyme lowers the free energy of activation by forcing the substrates to resemble the shape of the active site hence the transition state.
At what substrate concentration do enzymes follow zero-order kinetics?
Enzymes follow zero-order kinetics at substrate concentration above Km
(rate of the reaction is not influenced by concentration)
At what substrate concentration do enzymes follow first-order kinetics?
Enzymes follow first-order kinetics at substrate concentration below Km
(rate of the reaction is directly proportional to concentration)
At what substrate concentration will rate of the reaction not be influenced by concentration? What order of kinetics is this?
If the substrate concentration is above Km, enzymes follow zero-order kinetics.
At what substrate concentration will rate of the reaction be directly proportional to concentration? What order of kinetics is this?
If the substrate concentration is below Km, enzymes follow first-order kinetics.
Effect on reaction rate: slight increase in temp?
INCREASE reaction rate
Effect on reaction rate: large increase in temp? Why?
DECREASE reaction rate due to DENATURATION of proteins (enzymes)
Effect on reaction rate: slight increase or decrease in pH?
enzyme activity depends on the enzyme’s optimum pH
Effect on reaction rate: pH extremes? Why?
DECREASE reaction rate due to DENATURATION of proteins (enzymes)
What is the reciprocal of the Michaelis-Menten equation?
The LINEWEAVER-BURK PLOT is the reciprocal of the Michaelis-Menten equation
What is used to calculate Km and Vmax?
LINEWEAVER-BURK PLOT
What determines the mechanism of action of enzyme inhibitors?
LINEWEAVER-BURK PLOT
What is the LINEWEAVER-BURK PLOT? Its uses?
The LINEWEAVER-BURK PLOT is the reciprocal of the Michaelis-Menten equation
- used to calculate Km and Vmax
- determines the mechanism of action of enzyme inhibitors
What is any substance that can diminish the velocity of an enzyme-catalysed reaction?
An enzyme inhibitor
What type of inhibition competes for the binding site due to the similar shape of the substrate and inhibitor? Its effect on Vmax and Km? How is it reversed?
Competitive inhibition has an inhibitor with a similar shape of the substrate and competes for the binding site.
Km = increased
Vmax = not changed
Reverse by increasing substrate
“A rival manliligaw will steal Ms. Substrate’s time leaving you with more Kulelat Moments but your Valentine’s Mission is still the same. Reversed by increasing dates with Ms. Substrate.”
What type of inhibition halts catalysis by binding to the enzyme somewhere other than its binding site and changes the shape of the enzyme and its binding site? Its effect on Vmax and Km? How is it reversed?
Noncompetitive inhibition has an inhibitor that binds to the enzyme somewhere other than its binding site and halts catalysis.
Km = not changed
Vmax = decreased
Reverse by increasing enzyme
“Ms. Substrate’s strict father will still allow you to walk her home from school so no change in Kulelat Moments but will not allow her to have a boyfriend so Valentine’s Mission is decreased. Reversed by increasing Mr. Enzyme’s (your) patience.”
An inhibitor increased michaelis constant of a reaction but no change was observed in the Vmax. What type of inhibition is this? How is it reversed?
Competitive inhibition increases Km (michaelis constant) and doesn’t affect Vmax. It is reversed by increasing substrate concentration.
An inhibitor increased Vmax of a reaction but no change was observed in the michaelis constant. What type of inhibition is this? How is it reversed?
Noncompetitive inhibition increases Vmax and doesn’t affect Km (michaelis constant). It is reversed by increasing enzyme concentration.
What is the type of effector if the substrate itself serves as the effector?
Homotropic effector: substrate itself serves as the effector
What is the type of effector if the effector is different from the substrate?
Heterotropic effector: effector is different from the substrate
How is enzyme activity regulated?
- change substrate concentration
- through allosteric binding sites
- through covalent modification (phosphorylation or dephosphorylation)
- through induction or repression of enzyme synthesis
What is the significance of increased release of intracellular enzymes and elevated enzyme activity in the plasma? What is it useful for? Limitations?
Tissue damage is indicated by an increased release of intracellular enzymes and elevated enzyme activity in the plasma. It is useful for evaluating the prognosis of the px. Its diagnostic value is limited by the lack of tissue specificity.
What is the major diagnostic use of amylase?
Acute pancreatitis can cause elevated serum amylase.
What is the major diagnostic use ALT?
Viral Hepatitis can increase elevated serum ALT.
What is the major diagnostic use of creatine kinase?
Muscle disorders and myocardial infarction can cause serum elevation of CK.
What is the major diagnostic use of phosphatase?
Metastatic CA of the Prostate.
What is the major diagnostic use of gamma-glutamyl transpeptidase?
Various liver diseases
What is the major diagnostic use of ceruloplasmin?
Hepatolenticular degeneration or Wilson’s disease
What is the major diagnostic use of alkaline phosphatase?
Various bone disorders & obstructive liver diseases
70/M 5 days s/p tPA complains of sever chest pain and dyspnea. ECG: new-onset St-elevations in V1 & V2. What enzyme marker will best confirm re-infarct?
CK-MB will return to normal by the 5th day hence elevation will indicate re-infarct.
