ADENOSINE TRIPHOSPHATE ATP - PowerPoint Presentation

1. ADENOSINE TRIPHOSPHATEATP

2. ATPATP powers cellular work by coupling exergonic and endergonic reactionsATP Drives:Mechanical work like the beating of cilia, muscle contraction, cytoplasmic flow, chromosomal movementTransport work like pumping substances across membranesChemical work like polymerization (endergonic)

3. ATP

4. ATP’s M.O.Unstable bonds between phosphates are hydrolyzed in an exergonic rx.When the terminal (end) phosphate is hydrolyzed, the phosphate is removed leaving ADP ATP+H2OADP+PThis Rx releases –31kJ/mol (-7.3kCal/mol) in a lab.In a cell, -55kJ/mol (-13kCal/mol)Products are more stableUsually enzymatically controlledUsually transfers a Phosphate to another molecule, thus coupling the exergonic catabolosis with endergonic anabolosis.

5. ATP’s Energy TransferThe molecule that has the new phosphate attached (anabolic) is said to be phosphorylated or an activated intermediate, and is more reactiveHere’s a sample:Overall equation: Glu+NH3Gln(+14.2kJ/m) glutamic acid+ammoniaglatamine

6. Sample Equation: 2 Part Energy CouplingThe hydrolysis of ATP and phosphorylation of glutamic acidGlu + ATP  Glu-P + ADP unstable phosphorylated intermediateReplacement of the phosphate with the reactant ammoniaGlu-P + NH3  Gln + PNet change in Free Energy: -16.8kJ/mol…ATPADP+P=-31kJ/m, Glu+NH3Gln=14.2kJ/m

7. REGENERATION of ATPContinuous in CellVery quick: 10 million molecules of ATP are used and regenerated in each cell in each second!!!!ADP + PATP Free energy change=+31kJ/molEnergy to create ATP (endergonic) comes from cell respiration(exergonic)

8. !!Biological catalysts made of proteinsSpeed up reactions by lowering energy barriersA reaction may occur spontaneously if it releases free energy, BUT it may go too slowly to be of much use in living cells.Enzymes help with thisActivation Energy (free energy of activation): The amount of energy that reactant molecules must absorb to start a reactionTransition State: Unstable condition of reactant molecules that have absorbed enough energy to react. ENZYMES

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10. INDUCED FITA change in the shape of an enzyme’s active site which is induced by the substrate.This brings its chemical groups into positions which enhance their ability to interact with the substrate and catalyze the reaction.

11. Substrate specific (3-D Shape of protein is responsible!!!)Substrate+EnzymeEnzyme-Substrate complexProduct+EnzymeBinds to active site of substrate

12. ACTIVE SITESRestricted region of an enzyme molecule which binds to the substrateUsually a pocket or groove on the protein’s surfaceFormed with only a few amino acidsDetermines enzyme specificity with fit to substrateChanges its shape in response to substrate

13. The Active Site is an Enzyme’s Catalytic CenterThe entire enzymatic cycle is quite rapidEnzymes lower activation energy and speed up reactionsThe initial substrate reaction partly determines the rate of an enzyme controlled reaction

14. The Enzymatic CycleSubstrate binds to the active site forming an enzyme-substrate complex. They are held together by weak interactionsThe substrate causes an induced fit of the enzyme’s active site. The side chains of a few amino acids in the active site catalyze the reactionThe product departs the active site, the enzyme emerges unchanged

15. Enzymes Lower Activation Energy/Speed Up ReactionsThe active site can hold two or more reactants in the proper position so they can reactInduced fit can distort the substrate’s chemical bonds so less thermal energy is needed to break themThe active site can provide a micro-environment conducive to certain reactions (lower pH, etc.)Side chains of active site amino acids may participate directly in the reaction

16. Substrate Concentration:Rate of ReactionThe more substrate concentration, the faster the Rx (up to a certain point)If there is enough substrate, the enzyme can be thoroughly engaged or saturatedWhen this happens, the speed that the active site can convert reactants to products controls the reaction rateAdding more enzyme at this point sppeds the reaction up

17. Enzyme Substrate Concentration.

18. A Cell’s Physical and Chemical Environment Affects Enzyme ActivityEffects of Temperature and pHCofactorsEnzyme inhibitors

19. The Effects of TemperatureOptimal temperature affords the greatest number of molecular collisions without denaturing the enzymeTo a point, increased temp causes a faster rate. This point above the optimal temp, where the bonds holding the active conformation break, is called denaturation. Optimal temp. for humans: 35-40 degrees C

20. Temperature on Enzymes.

21. The Effects of pHWhile some enzymes work best at very high/low pH, the optimal range of human enzymes is 6-8Exception: PEPSIN in stomach: optimal pH pH of 2

22. pH on Enzymes.

23. CofactorsSmall nonprotein molecules required for proper enzyme catalysisMay bind tightly to the active siteMay bind loosely to both active site and substrateSome are inorganic (zinc, iron,copper)Some are organic and are called coenzymes (most vitamins)

24. Cofactors.

25. Enzyme InhibitorsCertain chemicals can selectively inhibit enzyme activityInhibition can be irreversible if the inhibitor attaches by covalent bondsIt can be reversible if it attaches by weak bonds

26. Competitive InhibitorsChemicals that resemble an enzyme’s normal substrate and compete with it for the active siteBlock active site from the substrateIf reversible, the effect of these inhibitors can be overcome by increased substrate concentration

27. Noncompetitive InhibitorsInhibitors which bind to a part of the enzyme other than the active siteCauses the enzyme to change its shape so the active site cannot bind substrateMay act as metabolic poisons (DDT, antibiotics)Selective enzyme inhibition is an essential mechanism in the cell for regulating metabolic reactions

28. Competitive and Noncompetitive Inhibition.

29. The Control of MetabolismMetabolic pathways are regulated by controlling enzyme activityAllosteric regulationFeedback inhibitionCooperativity

30. Allosteric RegulationAllosteric Site: A specific receptor site on the enzyme OTHER than the active siteMost enzymes with these have 2 or more polypeptide chains, each with its own active site. Often found where the subunits joinAllosteric enzymes have one active, one inactive conformationBinding an ACTIVATOR to an allosteric site stabilizes the active conformationBinding an INHIBITOR to an allosteric site stabilizes the inactive conformationEnzyme activity changes continually with changes in activators/inhibitorsSubunits may interact so that one activator/inhibitor at one site causes a change in the active sites of the other subunits

31. Allosteric Regulation.

32. Feedback InhibitionRegulation of a metabolic pathway by its end product which inhibits an enzyme within the pathway ThreonineABCDIsoleucineEnd product andAllosteric inhibitor of enzyme 1Feedback InhibitionEnz 1Enz 2Enz 3Enz 4Enz 5This prevents the cell from wasting chemicalResources by making too much product

33. Feedback Inhibition.

34. CooperativitySubstrate molecules themselves may enhance enzyme actionThe binding of the substrate to the active site of one subunit induces a conformational change which enhances substrate binding at the active sites of the other subunits

35. Cooperativity.

36. The localization of enzymes within the cell helps order metabolismThe structure of the cell compartmentalizes and orders metabolic pathwaysSome enzymes/enzyme complex stay in one place because they are part of a membraneOthers are bound in membrane enclosed organelles