BIOLOGY 123 EXAM 3 QUESTIONS AND
100% VERIFIED CORRECT ANSWERS!!!
Enzyme
Biological catalyst that accelerates chemical reactions.
Enzymes: How do they work?
Enzymes increase the rate of (catalyze) a reaction by lowering the activation energy (Ea) of a
reaction = the minimum amount of energy it takes to get a chemical reaction started.
Active Site
Region on enzyme where substrate binds.
If I fits, I sits!
Substrate
Reactant molecule that enzymes act upon.
Product
Substance formed from enzymatic reaction.
Enzymes: What are they made of?
•Usually made of protein, but sometimes made of RNA (ribozymes)
•Complete enzyme called Holoenzyme (looks like “whole” enzyme) has:
•A protein component called the apoenzyme plus
•Cofactors (ex. trace metals or organic electron carriers – also called coenzymes) which may
assist in the reaction and are recycled
•Example: NAD+ or thiamine pyrophosphate
•We often get precursors for these cofactors from vitamins in our diet
Holoenzyme
,Whole enzyme. apoenzyme + cofactor
apoenzyme
protein portion of an enzyme
Cofactors
Any nonprotein molecule or ion that is required for the proper functioning of an enzyme.
Cofactors can be permanently bound to the active site or may bind loosely with the substrate
during catalysis
Where do enzymes work?
Highly specific – only reactants that fit in the active site can sit in the active site (if I fits I sits!)
•Enzymes can be located inside or outside the cell
•Endoenzymes: intracellular (inside the cell)
•Exoenzymes: extracellular (outside the cell)
Endoenzymes
retained intracellularly and function there
Exoenzymes
transported extracellularly, where they break down large food molecules or harmful chemicals
How are enzymes regulated?
competitive inhibition and allosteric regulation
Enzymes are like lights:
•Turn it off when you don’t need it (inhibition)
•Turn it on when you do need it (activation)
Activation Energy
Energy required to initiate a reaction.
, Enzyme Regulation
Mechanisms controlling enzyme activity and function.
Reversible Inhibition
Temporary inhibition of enzyme activity.
Competitive Inhibition
Inhibitor competes with substrate for active site. (Molecular musical chairs)
Noncompetitive Inhibition
Inhibitor binds elsewhere, reducing enzyme activity. (Molecular recliner)
Allosteric Site
Site on enzyme where molecules can bind, altering activity. (other than binding site) (molecular
recliner lever)
Irreversible Inhibition
Permanent loss of enzyme activity due to inhibitor. (permanently broken recliner)
Why would a cell want to inhibit its own enzymes?Regulation!
(Lucy and Ethel at the chocolate factory - metaphor for feedback inhibition)
•So it doesn’t overproduce and accumulate a product
•It’s energetically expensive to produce products – saves energy
•Some end products can be toxic when they accumulate.
•When an end-product itself is used to turn off an enzyme = feedback inhibition
Feedback Inhibition
End product inhibits an earlier step in pathway.
Constitutive
Constantly expressed regardless of environmental conditions.
100% VERIFIED CORRECT ANSWERS!!!
Enzyme
Biological catalyst that accelerates chemical reactions.
Enzymes: How do they work?
Enzymes increase the rate of (catalyze) a reaction by lowering the activation energy (Ea) of a
reaction = the minimum amount of energy it takes to get a chemical reaction started.
Active Site
Region on enzyme where substrate binds.
If I fits, I sits!
Substrate
Reactant molecule that enzymes act upon.
Product
Substance formed from enzymatic reaction.
Enzymes: What are they made of?
•Usually made of protein, but sometimes made of RNA (ribozymes)
•Complete enzyme called Holoenzyme (looks like “whole” enzyme) has:
•A protein component called the apoenzyme plus
•Cofactors (ex. trace metals or organic electron carriers – also called coenzymes) which may
assist in the reaction and are recycled
•Example: NAD+ or thiamine pyrophosphate
•We often get precursors for these cofactors from vitamins in our diet
Holoenzyme
,Whole enzyme. apoenzyme + cofactor
apoenzyme
protein portion of an enzyme
Cofactors
Any nonprotein molecule or ion that is required for the proper functioning of an enzyme.
Cofactors can be permanently bound to the active site or may bind loosely with the substrate
during catalysis
Where do enzymes work?
Highly specific – only reactants that fit in the active site can sit in the active site (if I fits I sits!)
•Enzymes can be located inside or outside the cell
•Endoenzymes: intracellular (inside the cell)
•Exoenzymes: extracellular (outside the cell)
Endoenzymes
retained intracellularly and function there
Exoenzymes
transported extracellularly, where they break down large food molecules or harmful chemicals
How are enzymes regulated?
competitive inhibition and allosteric regulation
Enzymes are like lights:
•Turn it off when you don’t need it (inhibition)
•Turn it on when you do need it (activation)
Activation Energy
Energy required to initiate a reaction.
, Enzyme Regulation
Mechanisms controlling enzyme activity and function.
Reversible Inhibition
Temporary inhibition of enzyme activity.
Competitive Inhibition
Inhibitor competes with substrate for active site. (Molecular musical chairs)
Noncompetitive Inhibition
Inhibitor binds elsewhere, reducing enzyme activity. (Molecular recliner)
Allosteric Site
Site on enzyme where molecules can bind, altering activity. (other than binding site) (molecular
recliner lever)
Irreversible Inhibition
Permanent loss of enzyme activity due to inhibitor. (permanently broken recliner)
Why would a cell want to inhibit its own enzymes?Regulation!
(Lucy and Ethel at the chocolate factory - metaphor for feedback inhibition)
•So it doesn’t overproduce and accumulate a product
•It’s energetically expensive to produce products – saves energy
•Some end products can be toxic when they accumulate.
•When an end-product itself is used to turn off an enzyme = feedback inhibition
Feedback Inhibition
End product inhibits an earlier step in pathway.
Constitutive
Constantly expressed regardless of environmental conditions.
