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27 Cards in this Set
- Front
- Back
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What are the 3 ways in which Enzymes and Substrates interact? |
1) Lock and Key = Substrate is "key" that fits into rigid enzyme "lock"
2) Induced Fit = Substrate is rigid "lock" and enzyme is "key"
3) Transition State Stabilization = substrate binds to the enzyme and the enzyme causes the substrate to change shape and lock into the enzyme |
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What types of interactions hold E-S complex together? (in order from strongest to weakest) |
1) Electrostatic Interactions 2) H-Bonding 3) Hydrophobic Interactions 4) Van Der Waals Forces |
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6 Classes of Enzymes and Function |
1) Oxidoreductases = dehydrogenases, redox
2) Transferases = transfer chemical group from one substrate to another; kinases
3) Hydrolases = Transferases with water as acceptor
4) Lyases = breakdown of substrate; no transfer only removal
5) Isomerases = Isomerases; change the structure of the substrate
6) Ligases = Catalyze the joining of two substrates; ATP required |
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What is the active site of an enzyme? And what types of residues are they lined with? What are the top 3 catalytic residues? |
1) Active sites are "docking sites" on an enzyme where substrates bind and a reaction occurs.
2) lined with both unreactive hydrophobic residues, and reactive polar catalytic residues
3) His, Asp, Glu |
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What is alanine scanning? Use the example regarding Glu-165. |
1) Alanine scanning occurs when active catalytic residues are mutated into alanine (inactive) residues. If the enzyme no longer functions, then it can be said that the original residue had catalytic properties.
2) Glu-165 was first mutated into Asp-165, and the rate was slowed 1000X. Then Glu-165 was mutated into Ala-165, and the reaction did not occur at all. |
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Enzyme reactions are controlled solely by ____________. |
- Diffusion |
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What are the meanings of K1, K-1, and K2? |
1) K1 is the rate constant of the E-S complex formation
2) K-1 is the rate constant of the E-S complex dissociation
3) K2 is the rate of product formation |
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What are first and zero order reactions? |
1) First order reactions = rate and rate constant are dependent on both [E] and [S]
2) Zero order reactions = rate and rate constant are only dependent on [E], as a point has been reached where the enzyme is saturated with substrate |
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What is the Vmax and what is Kcat? How do the two differ? |
1) Vmax is the maximum velocity under current conditions and occurs at zero order.
2) Kcat is the rate of product formation under all E conditions. The amount of enzymatic reactions that take place in one second |
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What is Km? And what do high and low Km values mean? |
1) Km is the substrate dissociation constant, and the concentration at which 50% of the substrate is bound and 50% is not. Basically how tightly S binds to E
2) Lower Km = higher affinity, tighter binding Higher Km = Lower affinity, weaker binding |
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What is the equation for Kcat? What are the equations for K2 at first and zero order? What is the equation for catalytic proficiency? |
1) Kcat = vmax/[E]
2) K2 = kcat/km
3) K2 = Kcat
4) Rate constant with enzyme/rate constant without enzyme |
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What are the types of reversible inhibition of non-allosteric enzymes? and what are some of the subtypes of these larger types? and how do they act? |
1) Competitive a) Classical = Inhibitor looks like substrate and competes for access to the active site b) Non-Classical = Inhibitor binds to another site on the enzyme, which then changes the shape of the active site and inhibits the substrate from binding
2) Non-competitive = Inhibitor binds to another spot on the enzyme but only changes the shape of the active site slightly so that the substrate can still bind. This slight conformational change does not allow E to turnover any more
3) Uncompetitive = The Inhibitor only binds to another spot on the enzyme once the E-S complex has formed. There is never a chance for competition, and the enzyme is locked into one place. |
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Non-allosteric enzymes vs. Allosteric Enzymes |
- Allosteric enzymes only have one type of binding site, and its binding properties do not change
- Non-Allosteric enzymes have alternative conformations that affect the behavior of the proteins and substrate binding. There are multiple types of binding sites for multiple proteins, and they do not fit M/M model of Kinetics. They ALL have Quaternary structure |
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Two conformations of Allosteric Enzymes and their locations on the curve. |
1) T (taut) conformation - binds S less tightly, higher Km - located near the base of the curve
2) R (relaxed) conformation - binds S more tightly, lower Km - Along the steep slope of the curve |
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What are the 2 models of allosteric behavior? And give details of each mechanism. |
1) Concerted Model = all subunits change conformation simultaneously, R and T begin in equilibrium and then the reaction cycle favors R even though equal access to both.
2) Sequential Model = The substrate comes in and binds to the T form, this binding induces a conformational change of one subunit into the R form. The next substrate then comes in and binds while also changing the other subunit to the R form. |
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Even though Heme seems to hold and carry the oxygen, why is hemoglobin needed? |
-Hemoglobin is needed to regulate what enters and exits the heme pocket and provides support for O2 binding. Hemoglobin also keeps O2/Heme complex soluble in order for transport |
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What are the two conformations of Hemoglobin? Why are both high and low affinity areas needed for hemoglobin to function? What is the function of 2,3-BPG? |
1) Oxyhemoglobin (R Form) and Deoxyhemoglobin (T Form)
2) Need high affinity to be able to pick up oxygen in the lungs. Need high affinity to be able to transport oxygen through the blood. Need low affinity in the tissues to release oxygen.
3) 2,3-BPG acts as an inhibitor that binds to hemoglobin and locks it in the T form. This can be beneficial when releasing oxygen to the tissues. |
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What are anomers? And what is the anomeric carbon? What is mutarotation? |
1) Isomers that differ at the anomeric carbon
2) The carbon which contains an OH and can be situated in the alpha or beta form
3) The shift between alpha and beta anomers |
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Saccharides are held together by ___________ bonds. |
- Glycosidic |
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Anabolism is a __________ process that leads to the _____________ of cofactors. Catabolism is a _________ process that leads to the _______________ of cofactors. |
1) Reductive; Oxidation
2) Oxidative; Reduction |
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What is steady state? And what is flux? |
1) Steady state is when a reactant stays at a constant concentration even as the process proceeds. NOT AT EQUILIBRIUM
2) Flux is the movement of products through a pathway. |
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What are the types of cofactors and the sub-types of each of these? |
1) Metal Ions a) Activator Ions = do not participate directly b) Metalloenzymes = participate directly
2) Co-Enzymes a) Cosubstrate = binds to the active site and eventually returns to its original state b) Prosthetic Group = bound to the enzyme at all times; part of the active site; non-protein component |
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What type of metabolic process is glycolysis? In simple terms, what is glycolysis? What type of conditions does glycolysis occur under? Where does the glycolysis reaction occur? |
1) Catabolic
2) Conversion of one molecule of glucose to two molecules of pyruvate
3) Anaerobic Conditions
4) Cytosol
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Which phase is the committed step of glycolysis? And why? What is the first step in which ATP is produced? |
1) Step 3; from Fru-6-P to Fru 1,6-BisP
2) High Delta G and requires energy to occur
3) Step 7 |
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What are the pathways that pyruvate can take next under aerobic conditions? Under anaerobic conditions? |
1) Pyruvate => Acetyl CoA => TCA Cycle => Oxidative Phosphorylation Pyruvate => Oxaloacetate => Gluconeogenesis
2) Pyruvate => Lactate Pyruvate => Ethanol |
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Which steps of glycolysis are regulated? Why are these steps regulated? |
1) Steps 1, 3, and 10
2) Large Delta G, Far from EQ, Losing energy, not reversible |
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What happens during the regulation at each of these steps? |
1) Step 1 - Hexokinase is inhibited by glc-6-P - Low Glc-6-P binds Glc-6-p isomerase - High Glc-6-P binds Glc-6-P isomerase and Hexokinase
2) Step 3 - PFK-1 inhibited by ATP - PFK-1 Activated by AMP - PFK-1 Inhibited by Citrate - PFK-1 Activated by F-2,6-BP
3) Step 10 - Pyruvate Kinase inhibited by F-1,6-BP - Feedforward Activation |
