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41 Cards in this Set
- Front
- Back
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Do enzymes change the equilibrium of a rxn?
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No... only rate (or how fast the rxn reaches equilibrium)by lower activation energy
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In E + S <-> ES... name the reactants and products
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E = enzyme
S = substrate ES = Michaelis complex (reversible) |
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In A --> P, how do you determine the rxn velocity... and describe its curve
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v = k [A]
a straight line |
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In an ezyme catalyzed rxn, what eventually happen when your substrate concentration saturates the enzymes?
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V-max... at ES complex formation
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At low [substrate], what would you expect?
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velocity proportional to [S]... a straight line
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So, with respect to the work of the enzyme, what is happening at v-max?
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it's working as fast as it can, when a substrate leaves the binding site another enters.
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a. When is v virtually independent of [S]?
b. and what is the rate order at that point? |
a. At high concentrations
b. zero order . |
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what portion of the total enzyme do active sites take up of the surface?
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Small
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What is going on in the active site of an enzyme?
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residues directly participate in the making and breaking of bonds.
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In terms of the active site, what is important the sequence or the folding of the residues?
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most important is the folding which is actually a result of the sequence.
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How does the enzyme recognize the substrate?
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a. electrostatic force
b. hydrogen bonding c. van der Waals interactions d. hydrogen bonds e. various hydrophobic interactions in which water molecules are stripped off the substrate. . |
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What makes the enzyme and the substrate come together?
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Hydrophobic effects
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What role do the enzymes play in attracting the substrate?
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the crevices are hydrophobic, which excludes water and enhances catalysis. (like an SN2 rxn where a nucleophile and an electrophile can come together.)
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Was Emil Fischer right about the lock and key hypothesis?
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No
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What is Koshland's Induced fit hypothesis?
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After binding to the substrate, the enzyme undergoes a conformational change.
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What effect does an enzyme have that causes the lowering of the activation energy and thus speeds up the rxn?
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They stabalize the transition state.
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What is a Kcat or k2 number?
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the number of substrate molecules converted to product by a single enzyme per unit time.
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What is the Michaelis-Menten equation?
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v = k2[ET][S]÷km+[S], where
v-max = k2[ET] k2=kcat conversion per enzyme [S} = [substrate] km = a given substrate constant... thus, v= Vmax[S]÷ Km + [S] . |
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What happens when the substrate concentration is high... or [S]≥ Km?
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Ignore Km, thus, [S] cancels and...
V = Vmax |
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What happens when the [S]< Km?
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v = (Vmax/Km)[S]
a. now km is much more important b. and the substrate demoninator is ignored. . |
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what it the velocity of a rxn when km=[S]?
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v=Vmax/2
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a. What happen if you're near your Km and you double or half your [S]?
b. How is this relevent to cells? . |
a. It makes a big difference
b. if the [S] is near its km then varying it's [S] can have a big effect on the rate of product formation. . |
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Since V-max is never reached, how do you determine Km, if you don't know Km you don't know V-max?
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a. Take the inverse of velocity / the inverse of the [S], then
b. take two points and draw a staight line, then c. y-int = 1/V=max d. x-int = -1/Km . |
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What is acetylpepstatin?
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An HIV protease inhibitor
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What effect does a small KI (for an inhibitor) have on the rxn rate?
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small KI means more EI (inhibitor in the enzyme) and less enzyme is available for the substate.
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ON the Lineweaver-Burk plot, what does a sleeper slope when a competitive inhibitor is added?
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steeper slope, slower rxn... not as much enzyme available for substrate.
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How will a competitive inhibitor effect the V-max?
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it will have no effect... 1/V-max is always at the Y-int... you just have to add more substrate to out compete the competitive inhibitor to achieve V-max.
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Which 3 amino acids undergo phosphorylation
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serine, threonine, tyrosine
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a. Is an enzyme activated by a protein kinase or a protein phosphatase (in the presense of ATP or water)?
b. is this reversible? . |
phoshorylation or dephosphorylation can activate or deactivate.
it is reversible . |
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a. In protein kinase phosphorylation, what is the phosphoryl donor?
b. In protein phosphatase dephosphorylation, what is the phosphoryl acceptor? |
a. ATP
b. H2O |
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Is phosphorylation permanent?
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No, these rxns are reversible
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Is prenylation permanent?
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Yes
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What is prenylation?
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It is the adding of 5-C aliphatic moiety (very lipophilic) that anchor proteins to the membrane... (Farnesyl and Geranylgeranyl)
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What is the role of ras
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The role of Ras is to send a growth-promoting signal through a MAP kinase cascade
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What two proteins phosphorylate and dephosphorylate ras? and which is activating?
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GEF phosphorylates - activates
GAP dephosphorylates |
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Why is it that inhibiting the prenylation of ras a possible cancer therapy?
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Prenylation traps ras at the membrane where it activates the kinase cascade... freeing it will inhibit its role.
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what is an allosteric enzyme?
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Allosteric enzymes are enzymes whose activity is modulated by small molecules that reversibly bind to a site other than the active site... changing the enzymes conformation.
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Are allosteric enzymes activating or inhibiting?
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Either one
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T/F: all enzymes exhibit Michaelis-Menten kinetics.
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False, allosteric enzymes do not.
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which type of enzyme gives a hyperbolic curve and which a sigmoid curve?
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a. allosteri enzyme = sigmoid
b. non-allosteric enzyme = hyperbolic. . |
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Which type of enzyme is often inhibited by the end product?
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allosteric enzyme.
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