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56 Cards in this Set
- Front
- Back
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Enzymes can be __ or __
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Proteins or RNA
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In one sentence, how to enzymes catalyze reactions?
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Enzymes catalyze reactions by stabilizing transition states.
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What determines the specificity of an enzyme?
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The interactions of substrate with enzyme, as a result of 3D structure of enzyme protein.
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What are tightly bound cofactors called?
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Prosthetic Groups
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What are small organic molecules that act as cofactors called?
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Coenzymes
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What are coenzymes?
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Small organic molecules that act as cofactors (activating apoenzyme). Usually loosely associated with enzyme; can be used by a variety of enzymes.
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How can we tell if a reaction will occur spontaneously?
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If ∆G is negative = exergonic
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What does exergonic mean?
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∆G is negative, and the reaction can occur spontaneously
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What is ∆G if a system is at equilibrium?
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Zero -- no net change can take place
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What does it mean if ∆G = 0?
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The system is at equilibrium and no net change can take place
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What is ∆G if a reaction cannot occur spontaneously?
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Positive = endergonic
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What does it mean if ∆G is positive?
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The reaction can't occur spontaneously, it is said to be endergonic
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What does the ∆G of a reaction depend on?
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The free energy of the products (final state) minus the free energy of the reactants (initial state). Does not depend on the mechanism of reaction
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Does the mechanism of the reaction have an effect on the ∆G (whether the reaction can occur spontaneously)?
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No, only depends on free energy of products and reactants
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Does ∆G tell us about the rate of reaction?
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No. Tells us whether reaction can occur spontaneously, but not whether it is at a realistic rate.
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What does the free energy of activation tell us?
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The rate of reaction. Largely unrelated to the ∆G of the reaction.
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What can enzymes alter?
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Can alter reaction rate.
NOT reaction equilibrium. |
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How do enzymes accelerate reactions?
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They facilitate the formation of transition states. They decrease the activation energy.
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What is "activation energy"?
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The difference in free energy between transition state and substrate. Also known as Gibbs free energy of activation.
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Do enzymes shift equilibrium positions?
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No
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What accounts for the equilibrium of a reaction?
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The free energy of reactants and products
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What are the attractions between enzyme and substrate?
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Weak, noncovalent attractions such as hydrogen bonds or van der Waals.
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What is the study of rates of enzyme-catalyzed reactions called?
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Enzyme Kinetics
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What is competitive inhibition?
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The inhibitor binds to the same active site as the substrate
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How does a competitive inhibitor work?
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It diministhes the rate of catalysis by reducing the proportion of enzyme molecules bound to a substrate
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What types of inhibition can be overcome by adding more substrate?
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Competitive inhibition (more substrate - more likely it will bind to enzyme rather than inhibitor binding to enzyme). Uncompetitive inhibition cannot be overcome by adding more substrate.
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What is non-competitive inhibition?
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The inhibitor and substrate have different active sites. Cannot be overcome by adding more substrate.
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What does the formation of ES complex depend on?
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Both the [S] and [E]:
more like a 2nd order reaction: E+S ⇋ ES ⇋ E+P |
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What is noncompetitive inhibition?
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Inhibitor binds to non-active site. Substrate can still bind, but no product can form from ESI.
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What type of inhibition prevents substrate from binding to enzyme?
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Competitive inhibition
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What type of inhibition occurs when inhibitor binds to site other than the active site: substrate can still bind but no product is formed?
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Noncompetitive inhibition
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What are the different types of inhibition?
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Reversible:
* Competitive * Non-competitive |
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What does it mean if:
ΔG < 0 |
Exergonic: reaction will occur spontaneously
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What does it mean if:
ΔG > 0 |
Endergonic: needs an input of energy for reaction to occur
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Does ΔG correlate with rate of reaction?
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NO
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Competitive Inhibition
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What type of inhibition is this?
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What does non-competitive inhibition look like?
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Non-Competitive Inhibition
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What regulates enzymes
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Allosteric Regulation
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What is a Ligand?
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An ion or molecule attached to a metal atom by coordinate bonding.
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What does allostery refer to?
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A change in shape as result of the binding of a ligand
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Give two examples of inorganic cofactors
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Mg and Zn
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Give two examples of organic cofactors
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Vitamins and Coenzyme A
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What is a distinguishing feature of an allosteric enzyme?
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The presence of allosteric sites "regulatory sites"
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Are allosteric sites separate from the active sites?
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Yes
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What are the two forms of allosteric enzymes
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low affinity and high affinity forms
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What binds the alloseric site?
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Allosteric effector
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What does the allosteric activator do?
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Stabilizes active state of allosteric enzyme
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What does the allosteric inhibitor do?
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Stabilizes inactive state of allosteric enzyme
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What is an example of allosteric enzyme cooperativity and how does it work?
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Oxygen binding in Hb. Substrate binds to activation site and changes enzyme shape which increases catalytic activity
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What is another term for "end product inhibition"?
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Feedback inhibition
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Describe Feedback inhibition
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An end product binds to the allosteric site which changes the enzyme shape so that the initial substrate cannot bind with the active site.
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In terms of thermodynamics, what can photosynthesis be thought of as?
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An anabolic process
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What bonds the phosphate groups in ATP?
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phosphoanhydride bonds
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What two macromolecules are bonded by ester linkages?
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ATP and lipids
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What type of reaction occurs with the hydrolysis of ATP
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Exergonic
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What four ways do enzymes lower the Energy of Activation?
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Active site act as template
Induced fit Suitable micro environment in active site covalent bond reorganization |
