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39 Cards in this Set
- Front
- Back
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What type of enzymes mostly affect the rate of a reaction? |
Regulatory enzymes |
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What are the 4 ways through which enzymes can be regulated? |
Allosteric modulators (noncovalent), (reversible) covalent modification, binding by (other) regulatory proteins, or proteolytic cleavage (irreversible) |
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Regulation in which the substrate and modulator are identical is called... |
Homotropic |
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When the modulator is a molecule other than the substrate, the enzyme is said to be... |
Heterotropic |
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T/F: The properties of allosteric enzymes are significantly different from those of simple nonregulatory enzymes. |
True |
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Describe the basic structure of ATCase, which catalyzes an early step in the biosynthesis of pyrimidine nucleotides, i.e. the reaction of carbamoyl phosphate and aspartate to N-Carbamoylaspartate. |
12 polypeptide units: 6 catalytic, and 6 regulatory. The regulatory are promoted with ATP which activates ATCase and inhibited with CTP which serves to deactivate ATCase and is one of the products of the end of the pathway. |
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Because allosteric enzymes do not have a hyperbola in the M-M and thus do not have an M-M, what do they have and what does this represent? |
[S](0.5) or K(0.5), which represents the concentration of S giving half-maximal velocity of the reaction catalyzed by an allosteric enzyme |
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Why does simply the binding of the 2 SUBSTRATES to ATCase exhibit sigmoidal behavior? |
Because their binding alone actually increases the enzyme's activity |
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T/F: Because ATCase is regulated by both the binding of its substrates and the binding of allosteric modulators, it is both homotropic and heterotropic. |
True |
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How would you find K(0.5) on a sigmoidal curve? |
Find V(max) (asymptote), half it, and the [S] here is K(0.5) |
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What happens to K(0.5) when a positive modulator is added? Negative modulator? |
Positive - K(0.5) is less, which means the [S] at half maximal velocity is lower because less S is needed to reach Vmax because the pathway is positively promoted
Negative - K(0.5) is larger |
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Why enzymes catalyze the attachment of phosphoryl groups to specific amino acid residues of a protien? Which amino acids accept the phosphoryl group? |
Protein kinases; Ser, Thr, Tyr (and occasionally Histidine) |
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What catalyzes the removal of phosphoryl groups? |
Protein phosphatases |
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What is the purpose of glycogen phosphorylase? What are its two forms, and what enzymes interconvert the enzyme between these two forms? |
Glycogen phosphorylase takes adds Pi to one glucose of glycogen and thus removes it, making glucose 1-phosphate. The most active form is phosphorylase A which has 2 Pi groups on two Ser residues (one on each subunit), and it interconverts to phosphorylase B by phosphorylase phosphatase (B has no Pi bound to Ser) and back to A by phosphatase kinase |
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T/F: Consensus sequences in polypeptides define amino acids as a phosphorylation substrate. They could be basophilic, or prefer to phosphorylate bear a Pro residue, etc. |
True |
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What is the inactive precursor that is cleaved to form the active enzyme called? |
A zymogen (have the -ogen suffix) |
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The precursor of a NON-protease is not a zymogen, but rather a... |
Proprotein or proenzyme |
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What is trypsin, what is its precursor, and what inhibits its active form? |
Trypsin is a serine protease, its precursor is trypsinogen, and pancreatic trypsin inhibitor stops its activity in its active form |
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A mechanism that allows a very sensitive response to and amplification of a molecular signal is a... |
Regulatory cascade (can be initiated by proteolytic cleavage, phosphorylation, etc.) |
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What stimulates the blood-clotting cascade? What protease catalyzes this, what does it specifically catalyze, and what is its precursor? |
Cascade stimulated by platelets aggregating at a damaged blood vessel surface, which ultimately converts prothrombin to thrombin, a protease that converts fibrinogen to fibrin which allows for further platelet crosslinking |
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What does Factor VII make from Factor X, and what does this do that helps the clotting process? |
Factor VII catalyzes the conversion of Factor X to Factor Xa, which makes cleaves prothrombin to thrombin and this makes fibrin from fibrinogen |
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How does cAMP regulate glycogen phosphorylase? |
cAMP allosterically activates Protein Kinase A which catalyzes the phosphorylation and thus the activation of glycogen phosphorylase (B kinase, the enzyme that converts glycogen phosphorylase from inactive b to active a) |
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Briefly describe the flow of G-protein coupled receptors and its intermediates. |
Inactive G protein with GDP is activated by GTP-GDP Exchange Factors (GEFs) forming active G protein with GTP.
Active G protein activates downstream effector enzymes, like cGMP and adenyl cyclase.
Active G protein with GTP has its GTP hydrolyzed to GDP by GTPase, which is activated by GTPase activator proteins (GAPs) which themselves are activated by active G proteins! |
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Ok ok ok. So discuss the entire mechanism of the activation of glycogen phosphorylase, starting with the release of epinephrine. Other inhibitors? Activators? |
Epinephrine activated cAMP which activates PKA which activates phosphorylase kinase B which activates glycogen phosphorylase into its *"A"* form. Excess glucose deactivates the active A form in negative feedback. Glucagon (a hormone) activates phosphorylase B kinase for the creation of more active A form, and this makes sense because glucagon is released when blood sugar is too low. |
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What are the (pretty crappy) two ways in which you can regulate the AMOUNT of enzyme (and thus its activity levels)? |
Regulated gene expression and protein degradation (proteolytic cleavage) |
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Describe the structure and activation of PKA. |
PKA has 2 regulatory and 2 catalytic subunits; cAMP binds to the regulatory (leading to a conformational change) and so the regulatory subunits dissociate from the molecule, and the active sites of the catalytic subunits are free |
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Through what two NON-covalent interactions can phosphoryl groups change the conformation of the newly modified (i.e. phosphorylated) protein? |
Through hydrogen bonds and ionic interactions |
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What is the effect of the fact that one kinase can phosphorylate multiple target proteins? |
Signal amplification |
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cAMP, PKA, Ca2+ and calmodulin, and diacylglycerol are all forms of _ that... |
Input signals that activate protein kinases! |
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T/F: Hormone signaling and PKA regulation serves to regulate and coordinate multiple metabolic |
True |
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Functional digestive enzymes, hormone precursors, cellular proteins for programmed cell death, and structural proteins are all... |
Proproteins, i.e. targets of proteolytic cleavage |
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In the stomach, what enzyme converts trypsinogen to its product, and what is its product? |
Enteropeptidase converts trypsinogen to trypsin |
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What are packaged and stores in secretory granules (like in pancreatic cells), processed by specific proteolysis before release, and can bind to specific receptors on cells in other tissues? |
Prohormones |
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The most common genetic cause of hemophilia are mutations in Factor... |
VIII |
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Cyclin-dependent kinase 1 undergoes dephosphorylation to induce... |
Mitosis |
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"Some proteins are only expressed at certain times, for example at specific stages of the |
Temporal control |
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Methylation, ADP-ribosylion, and adenylylation are all other forms of... |
Covalent modifications |
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What are compartmentalizatino and local inhibition used for? |
To regulate proteases that have had peptides terminally and permanently cleaved! Local inhibition example of PTI (pancreatic trypsin inhibitor) |
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The regulation of the blood clotting cascade is another example of... |
Proteolytic processing |
