Lec3enzymecompetition

Molecular Biology of the Cell

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Unformatted text preview: Substrate concentration ? -- Monkeys & Peanuts Assumptions: – 1. monkeys are full and don’t eat peanuts – 2. peanuts can readily be stuck back together – 3. monkeys are just as likely to put the 3. peanuts back in the shells as they are to take them out. them Substrate concentration – Monkeys & Peanuts [S] = Concentration of peanuts(peanuts/m2) Time required per peanut: To find (sec/peanut) To shell (sec/peanut) Total (sec/peanut) Rate of shelling Per monkey (peanut/sec) Total (v) (peanut/sec) 0.10 1.0 9 1 10 1 Substrate concentration – Monkeys & Peanuts Monkeys [S] = Concentration of peanuts(peanuts/m2) Time required per peanut: To find (sec/peanut) To shell (sec/peanut) Total (sec/peanut) Rate of shelling Per monkey (peanut/sec) Total (v) (peanut/sec) 0.10 0.25 1.0 2.5 9 1 10 3 1 4 1 3 Substrate concentration – Monkeys & Peanuts Monkeys [S] = Concentration of peanuts(peanuts/m2) Time required per peanut: To find (sec/peanut) To shell (sec/peanut) Total (sec/peanut) Rate of shelling Per monkey (peanut/sec) Total (v) (peanut/sec) 0.10 0.25 0.5 1.0 2.5 5.0 9 1 10 3 1 4 1 1 2 1 3 9 Remember we started out with 10 monkeys total Substrate concentration – Monkeys & Peanuts [S] = Concentration of peanuts(peanuts/m2) Time required per peanut: To find (sec/peanut) To shell (sec/peanut) Total (sec/peanut) Rate of shelling Per monkey (peanut/sec) Total (v) (peanut/sec) 0.10 0.25 0.5 0.77 1.0 2.5 5.0 7.7 9 1 10 3 1 4 1 1 2 0.33 1 1.33 1 3 9 27 Thought Questions Thought What is happening at low concentration in terms What of enzyme binding and turnover, substrate concentration concentration High concentration….. Need to Graph? [S] = X axis V (peanuts shelled/time) = Y Axis Substrate concentration Substrate Substrate concentration Substrate What does Vmax tell us about an enzyme? What does Km tell us about an enzyme? Why is this important ? – Why study Km and V-max both give information about efficiency of an enzyme Km tells about the effective working concentration – iif the concentration is below the Km then the f reaction is very inefficient – preferred substrates vs. alternate substrates preferred V-max tells about "turnover" or how fast the enzyme can complete the reaction Can also tell a lot about inhibitors such as for control of the reaction or testing drugs Regulating Protein Activity Regulating 3 main categories of enzyme regulation 1. Feed back inhibition 2. Allosteric regulation 2. 3. Covalent modification – Phosphorylation/dephosphorylation Irreversible Inhibitors Irreversible Permanently bound to enzyme Nerve gas- affect nervous system Some heavy metals Not really an option for the cell!!! Enzyme Inhibition Reversible means of regulation is more common common Two ways inhibitors work Two – competitive inhibition: binds with active site binds Competing with the substrate Competing – non-competitive inhibition / Allosteric: binds binds with sites other than active site with Competitive inhibitor Competitive Resemble the substrate and competes Resemble with the substrate for active site binding with – (substrate analog) (substrate However it does not react or form the same bonds as the substrate. same principle of many drugs Competitive Inhibitor Competitive 1940s – end of WWII Probenicid BenzylPenicillin / Penicillin G Do not get caught up in the chemical details Allosteric regulation Allosteric allo = different or other, steric = structure or state allo structure Allosteric enzymes may be either inhibited or activated Allosteric inhibited activated by regulator substances by allosteric activator - where the a.a. binds to enzyme and allosteric changes active site to fit substrate – increases activity changes allosteric inhibitor - where the a.i. binds to enzyme and allosteric changes active site to NOT fit substrate - decreases changes differs from competitive inhibition Allosteric regulation Allosteric Can be positive or negative Negative effector usually decreases Vmax Postive effector can affect either Vmax, Km or both Postive Cells use Allosteric effectors to regulate reactions because that is the easiest way to control the enzyme Allosteric Regulation Allosteric Fig. 3­12 Double-Reciprocal Plot Double-Reciprocal Hard to extrapolate data using MichaelisMenton plot- hard to find exact data points Lineweaver-Burk double reciprocal plot of Lineweaver-Burk enzyme kinetics allows us to extrapolate data due to its linear nature. data Can find exact Vmax and Km Data is inverse form Double-Reciprocal Plot Double-Reciprocal Double Reciprocal Plot Double Slope of line = Km / Vmax Vmax Km can be calculated from the X-intercept Vmax from the Y-intercept Inverse relationship Km velocity Vmax Lower [s] Higher Allosteric Inhibitor Allosteric – Non change in Km / Vmax is decreased Non Competitive Inhibitors Non – Km – increased/ no change to Vmax A competitive inhibitor increase the Km but does not affect Vmax inhibitor Y- intercept is unchanged X - intercept is changed Normal Lower Substrate Concentration Higher Non-Competitive Non-Competitive Non-competitive inhibitor competes for a different site (allosteric effector ) Decreases Vmax ( higher y-intercept); usually with no change in Km (x intercept) inhibitor Normal Lower Higher Substrate Concentration Why does completive only effect only effect KM while non-completive only effect effect Vmax ? Vmax Lower V Non Competitive Competitive Normal Lower Km Higher Higher V Feedback Inhibition where a product of the reaction inhibits an enzyme Excess of the final product leads to inhibition. Feedback Inhibition Why does is Z (last product in the series) inhibit the path way? Why not Y or X ? How do we reverse? Negative feed back can be part of larger pathways and inhibit multiple pathways Enzyme regulation Enzyme covalent modification – calcium ions, phosphate, methyl, acetyl, calcium groups or derivatives of nucleotides groups – Act as additional side groups – these all cause conformational changes Kinases add a Phosphate Kinases Review Review Types of regulation (general) Types Feedback inhibition Feedback – Double-Reciprocal l Allosteric regulation l Covalent bonding of additional side chains ...
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This note was uploaded on 04/20/2010 for the course BIOL 4064 taught by Professor Dr.reyna during the Fall '09 term at Ouachita Baptist.

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