Nature and Properties of Enzymes Flashcards
All enzymes are proteins, with the exception of ……….
a small group of catalytic RNA molecules
What is a Cofactor
an additional chemical component needed by some enzymes for activity. It could be either one or more inorganic compounds or a coenzyme.
What is a coenzyme?
a complex organic or metallorganic molecule that some enzymes need to function.
What are prosthetic groups?
coenzymes or metal ions that are tightly or even covalently bound to the enzyme protein.
……….. is a complex, catalytically active enzyme + its bound coenzyme and/or metal ions
Holoenzyme
……… is the protein part of a holoenzyme
Apoenzyme or apoprotein
…….. is the ability of enzymes to differentiate between structurally similar substrates. Enzyme specificity is divided into two: Optical specificity and group specificity
Enzyme specificity
…………… is the portion on the enzyme molecules in direct contact with the substrate(s) during the transformation of the substrate(s) to products
Enzyme active site
An account on enzyme nomenclature and classification
Class one, Oxidoreductases: Catalyse oxidation-reduction reactions. E.g. dehydrogenases
Class Two, Transferases: Catalyse reactions involving transfer of a group from a donor to an acceptor e.g. amino transferase
Class Three, Hydrolases: Catalyze hydrolytic reactions e.g. the cleavage of C-O, C-N, and some other bonds
Class Four, Lyases: They catalyze reactions involving the removal of a group leaving a double bond or the addition of a group to a double bond. E.g. aldolases, dehydratases, etc.
Class Five, Isomerases: Catalyze reactions involving conversion of one isomer or compound to another. E.g. epimerases
Class Six, Ligases or Synthethases: Catalyze reactions where there is a joining together of two molecules + breakdown of the pyrophosphate bond of ATP or any similar triophosphate.
Describe the enzymatic code that was developed by IUC
First digit: represents the class
2nd digit: represents the sub class based on a characteristic of the enzyme
3rd digit: represents the sub sub class based on another characteristic of the enzyme
4th digit: represents the number assigned to the enzyme by EC
Enzyme with E.C. number: 1.1.1.1. is called ……….
Ethanol NAD+ 1- Oxidoreductase. E.C. 1.1.1.1.
What is enzyme kinetics
The study of the rate of enzyme catalyzed reaction in relation to changes in experimental parameters as a means to suggest the mechanism of each enzyme-catalyzed reaction.
Mention some factors affection enzyme-catalysed reactions
pH of the medium,
temperature,
enzyme concentrations.
……… is an energy barrier that must be surmounted before a reaction can proceed.
Activation energy
How do enzymes lower activation energy?
by binding the transition state intermediate tightly and the binding energy of this interaction effectively reduces activation energy and increases the reaction rate
………. is a surface that complements/best suited for the transition state in stereochemistry, position and charge.
Transition state intermediate
……… determines the ability of a chemical reaction to go to completion
Standard free energy change ΔG0
Represent standard free energy change mathematically
ΔG0 = - RT ln Keq
The binding of an enzyme to the transition state is endergonic. True or false
False. The binding of an enzyme to the transition state is exergonic
How does the binding of two or more reactants (substrates) to the enzyme’s surface, affect a reaction?
Proximity of the substrates on the enzyme’s surface, greatly increases the probability of productive collision between reactants
What’s the effect of enzymes on equilibrium position?
Enzymes do not alter the position of equilibrium; they only affect the rate at which the equilibrium can be obtained
What is the state of the enzymes at the end of the reaction?
They remain unchanged at the end of the reaction
How does the pH of the medium affect enzyme catalysed reactions?
by changing the native conformation (protein structure) of the enzymes
by changing the ionic state of the substrate. Thus leading to increase or decrease in affinity of their binding to enzymes.
Define optimum pH
pH at which there’s the highest percentage of residual activity i.e. pH at which the enzyme works best. Usually it’s between 5.0 and 9.0
………….. affects the magnitude and position of the equilibrium constant
Increase in temperature
State two assumptions made by Michealis and Menten to derive the relationship between velocity of the reaction and substrate concentration
The reaction goes through an enzyme- substrate complex intermediate
Rate of formation of the product is determined by the rate at which the E-S complex is broken down to a free enzyme and a product i.e. concentration of the E-S complex determines rate at which products are formed
In 1925, ………….. discovered that the assumption K1»K2
Briggs and Haldane
What’s the effect of activators on enzyme catalysed reactions?
They act by binding the enzyme into a catalytically active and stable state without, sometimes, themselves becoming involved in the reaction.
…….. Inhibitor binds covalently to the active site
Irreversible inhibitor
How do reversible inhibitors work?
Involves non-covalent bonding of the inhibitor with the enzyme at the active site or at any other place on the enzyme molecule
Mention physical means through which reversible inhibitors can be removed
dilution or dialysis,
increasing substrate concentration
Describe the classes of reversible inhibitors
Competitive inhibitors
- Inhibitor competes with substrate for the enzyme active site
- Always substrate analogues
- Vmax isn’t affected but Km is.
- Includes product and substrate inhibition
Non competitive inhibitors
- Dead-end complexes are formed
- Inhibitor binds to a site on the enzyme molecule different from the site that is meant for the substrate, or even binds to the ES complex, forming a dead- end.
- Not removed by increasing substrate concentration.
Uncompetitive inhibition
- Involves binding of inhibitor to enzyme- substrate [ES] complex only
- Alters the Vmax AND the Km
- Not removed by increasing substrate concentration
What is turn over number?
Turnover number refers to the number of moles of substrate converted to product per active site of the enzyme per second, when the enzyme is fully saturated.
……… is a substrate concentration at half the maximum velocity of an enzyme catalyzed reaction.
Km
Double Displacement Mechanism (Ping- Pong)
-There is a release of one or more products before all the substrates are bound to the enzyme active site.
- The enzyme interconverts between two stable form
Describe the sequential mechanism
- All the substrates bind to the enzyme active si te before products are formed
- Involves only one stable enzyme form which is the free enzyme
Describe the two classes of sequential mechanism
Sequential mechanism is further classified into two:
- Ordered sequential Mechanism: The substrate binds to the enzyme active site and the product leaves/ dissolves from the enzyme substrate in a compulsory ordered manner
- Random order sequential mechanism: Any substrate can bind first to the active site and any product can leave first.
What are the types of kinetic mechanism?
- Sequential Mechanism
- Double Displacement Mechanism/ Ping- Pong
