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58 Cards in this Set

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These are the protein catalysts that accelerate reactions, such as those in metabolic pathways, by reducing the initial energy (activation energy) necessary for them to proceed.
Enzymes
Does the enzyme change the equilibrium point of the reaction?
No
Does the enzyme change the rate at which the reaction is obtained?
Yes
Are enzymes consumed or changed as part of a reaction?
No
Are most enzyme reactions reversible?
Yes
Can a product synthesized by the enzyme also be decomposed by the same enzyme?
Yes
In an enzyme catalyzed reaction, is the activation energy higher or lower than an un-catalyzed reaction?
Lower
Of the two reactions (catalyzed and un-catalyzed) what is the overall change in free energy ( △G).
Unchanged
Are enzymes selective?
Yes. They may catalyze only one reaction or a specific class of closely related reactions.
What enzyme selectively catalyzes the breakdown of Urea?
Urease
What enzyme selectively catalyzes the hydrolysis of specific types of peptide bonds, enabling it to catalyze the hydrolysis of more than one type of peptide?
Chymotrypsin
The molecule on which the enzyme acts is called what?
Substrate
This three-dimensional site is the area where the substrate fits and is held in a particular orientation forming what?
Active site
Enzyme-substrate complex
What are the two models describing the enzyme-substrate complex?
Lock & key
Induced fit
This model holds that the spatial structure of an enzyme's active site is exactly complementary to the spatial structure of its substrate.
lock (enzymes active site) and Key (substrate)
This model describes the active site of an enzyme as having some flexibility of shape. When an appropriate substrate comes in contact with the active site, the confirmation of the active site changes such that it surrounds the substrate creating a close fit.
Induced fit hypothesis
Which is the more widely accepted model of the two?
Induced fit
Many enzymes require these non-protein molecules to become catalytically active.
Cofactors
True or false:
These cofactors aid in binding the substrate to the enzyme or in stabilizing the enzyme in an active conformation
True
An enzyme devoid of the necessary cofactors making it catalytically inactive is called what?
Apoenzyme
An enzyme containing the necessary cofactors is called what?
Holoenzyme
Cofactors can be bound to their enzymes by what two means?
Weak non-covalent interactions
Strong covalent bonds
Tightly bound cofactors are called what?
Prosthetic groups
Two important types of cofactors are called what?
Metal cations
Small organic groups (coenzymes)
True or false
Most coenzymes can be synthesized by the body
False
They must be obtained by diet as vitamin derivatives.
True or false
The lack of a particular vitamin can impair the action of its corresponding enzyme and lead to disease.
True
Clinical Correlation:
Thiamin is an important cofactor for several enzymes involved in cellular metabolism & nerve conduction. Thiamin deficiencies, often seen in alcoholics, results in the disease known as Wernicke-Korsokoff syndrome.
In this disorder, patients suffer from a variety of neurological deficits, including delirium, balance problems and in severe cases, the inability to form new memories.
True or false
The rate of an enzyme-catalyzed reaction is related to the concentrations of both enzyme and the substrate and environmental variables such as temperature and pH.
True
At highest concentrations of substrate, the reaction rate approaches what? At this point, increases in substrate concentration will no longer increase reaction rate.
Maximum velocity or Vmax
What model proposed in 1913, an enzyme-substrate complex , ES, is formed at rate k₁ from enzyme E and substrate S. The ES complex can dissociate into E and S at rate k₂, or form product P at rate k₃
Michaelis-Menton Model
Rates of enzyme-catalyzed reactions tend to double for every _ ºC increase in temperature until their optimal temperature is reached.
10ºC
What is the optimal temperature for enzymes operating in the human body?
37ºC
What happens to enzymes at higher temperatures?
They denature
Can partially denatured enzymes sometimes regain their activity upon being cooled.
Yes
What is the maximal activity pH of many human enzymes?
7.2 (the pH of most body fluids)
What pH does pepsin work best in?
pH of 2 because it works in the stomach.
Pancreatic enzymes work best around what pH?
8.5`
An enzyme with two or more active sites and may be composed of more than one subunit is called what?
Allosteric enzyme
True or false
An allosteric enzyme oscillates between two configurations.
True - An active state capable of catalyzing a reaction and an inactive state that can not.
What is the name of a molecule that binds with the enzyme other than a substrate?
Regulator
What are the two types of regulators.
Allosteric inhibitors
allosteric activators
Which one prevents the enzyme from binding to its substrate by stabilizing the inactive conformation.
Allosteric inhibitor
Which one stabilizes the active configuration promoting the formation of enzyme substrate complexes.
Allosteric activators
True or false
One type of allosteric effect increases the affinity of an enzyme for its substrate.
True
Sometimes the binding of the regulator at the allosteric site, or the binding of the substrate at one of the enzyme's active sites, may stimulate the other active sites on the enzyme to bind more efficiently by increasing their affinity for the substrate.
What blood component is composed of four subunits, each with its own oxygen binding site; the binding of oxygen at one increases the affinity for the remaining three active sites
Hemoglobin
Can an enzyme's activity be regulated by one of the products it catalyzes.
Yes
What are the three interferences with enzymatic activity.
Feedback inhibition
Reversible inhibition
Versible inhibition
Product D is an inhibitor modulator for enzyme 1. Thus when the concentration of D reaches some level, virtually all enzyme 1 molecules are inhibited and production of B (and thus C & D) is halted. The process is sometimes reversible and instantaneous; as D levels decrease, enzyme 1 inhibition decreases , and A is again converted to B. What type of interference is this?
Feedback inhibition - This allows organisms to avoid overproduction of metabolites.
Reactions with weak enzyme-inhibitor complexes that dissociate easily are referred to as what?
Reverse inhibition reactions
What are the two different types of reverse inhibition reactions?
Competitive inhibitors
Non-competitive inhibitors
Which one competes with the substrate directly by binding to the active site of the enzyme and are very similar in structure to the active substrate?
Competitive inhibitors
e.g. Melonate differs from succinate only in having an additional methyl group and is consequently recognized as succinate by the enzyme succinate dehydrogenase.
Can the presence of competitive inhibitor molecules be overcome?
Yes, by sufficiently high substrate concentrations.
Do non-competitive inhibitors interfere by binding on other sites on the enzyme?
Yes, and cause a conformational change such that enzyme can no longer bind substrate at its active site.
Can the presence of non-competitive inhibitor molecules be overcome by increasing the substrate?
No.
In this type of inhibition permanent damage is done to the active site, either by tight, covalent bonding of the inhibitor to the enzyme or by denaturation of the 3D structure of the active site.m This prevents the formation of the enzyme-substrate complex.
Irreversible inhibition.
What is an enzyme that is secreted in an inactive form & can be cleaved via physiological conditions to the active form of the enzyme.
Zymogen
What are these three zymogen cleaved to in the digestive tract?
Pepsinogen
Trypsinogen
Chymotrypsinogen
Pepsin
Trypsin
Chymotrypsin
Clinical Correlate
Methanol is enzymatically converted to toxic metabolites that can cause blindness and/or death. What can be IV administered as a treatment of choice to compete with the enzymes involved?
Ethanol