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Enzymes - PowerPoint PPT Presentation

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Enzymes. Cells build up and breakdown molecules in steps. Each step is helped along by enzymes. Structure:. Review Protein Structure. Enzymes are proteins. Made of amino acids Peptide bonds. The totality of an organism’s chemical reactions is called metabolism .

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    1. Enzymes

    2. Cells build up and breakdown molecules in steps. Each step is helped along by enzymes

    3. Structure: Review Protein Structure Enzymes are proteins • Made of amino acids • Peptide bonds

    4. The totality of an organism’s chemical reactions is called metabolism. A cell’s metabolism is an elaborate road map of the chemical reactions in that cell. Metabolic pathways alter molecules in a series of steps. Enzymesselectivelyaccelerate each step. The activity is regulated to maintain an appropriate balance of supply and demand. The chemistry of life is organized into metabolic pathways

    5. Catabolic pathwaysrelease energy by breaking down complex molecules to simpler compounds. This energy can be stored for later use. Ex. Cellular respiration Anabolic pathwaysconsume energy to buildcomplicated molecules from simpler compounds. Ex. Protein synthesis The principles that govern energy resources in chemistry and physics also apply to bioenergetics, the study of how organisms manage their energy resources.

    6. *these pathways intersectin such a way that the energy released from Cat. can be used to drive Anab. – transfer of energy is called Energy coupling (ATP very important…transfer energy from one reaction to another) • Living systems transform one form of energy to another in order to carry out essential life functions. • The laws of thermodynamics govern these energy transformations.

    7. Physical Science review: Energy • Defined as capacity to do work (move matter against opposing forces) • Exists in a variety of forms, and work of life depends on ability of cells to transform energy from one type into another

    8. Potential vs. Kinetic CLIP • Potential energy:stored energy that matter possesses because of its location or structure (Bio-chem pot E) Ex. Chemical energy in organic molecules, water in reservoir behind dam • Kinetic energy:energy of motion Ex. Water gushing through dam, light energy, heat energy

    9. Laws of thermodynamics • 1st-energy cannot be created or destroyed, only transferred/ transformed. • Also known as conservation of energy law.

    10. 2nd-in the course of energy conversions, the universe become more disordered(greater entropy). • Every energy transfer or transformation makes the universe more disordered.

    11. Gibb’s free energy equation ΔG = Δ H –T Δ S • Important to understanding metabolism. • Can predict which process/reactions can supply energy to do work. Free energy: Portion of a system’s energy that can be used to perform work. (Is “free” b/c is available for work, not because it does not cost the universe something…)

    12. Guest Speaker: MR. ANDERSDON…… What is FREE ENERGY????? Answer Brianna Sam Cory

    13. The measure of the disorder or randomness ΔG = Δ H –T Δ S • G = free energy change • ΔH=Change in heat content (enthalpy) • T= absolute temperature • ΔS= systems Entropy Once we know the value of “G” for a process, we can use it to predict whether it is exergonic or endergonic. • -G:releasing energy (exergonic/exothermic) • Spontaneous- (must give up heat or order) • Decreases the free energy • +G: absorbing energy (endergonic/endothermic) (or zero) ATP  ADP DGo= -30.5 kJ 1878-Willard Gibbs Free energy: Portion of a system’s energy that can perform work when temp & pressure are uniform throughout the system. (Is “free” b/c is available for work, not because it does not cost the universe something…)

    14. Exergonic – energy outward; proceed with a net release of free energy -usually releases energy in form of heat; these rxns occur spontaneously (ΔG is negative) Clip Endergonic– energy inward; absorbs free energy from its surroundings, containers for these rxns tend to feel cool (ΔG is positive)

    15. Function: • Enzymes speed up chemical reaction by lowering the activation energy (amount of energy needed to start the rxn).

    16. Potential Energy of products is less that Potential Energy of reactants, so energy is released-exothermic. • ---line shows same rxn w/enzyme. • Rxn can proceed more quickly.

    17. Potential Energy of products is more that Potential Energy of reactants, so energy is absorbed-endothermic. • ---line shows same rxn w/enzyme. • Rxn can proceed more quickly.

    18. Stop here • Do the 4 activities in Ch 8 • Take the “activities quiz” • Online; : AP Lab #2 • Go through the background info • Skip experiment • Take quiz • Tonight: • Read pages 141-157 • Take your own notes • Read Lab background information.

    19. How do they work: Enzymes • In simple terms, an enzyme functions by binding to one or more of the reactants in a reaction. • The reactants that bind to the enzyme are known as the substratesof the enzyme. • The exact location on the enzyme where substrate binding takes place is called the active site of the enzyme.

    20. Binding Specificity Enzymes can only bind to certain molecules The shape of the active site just fits the shape of the substrate, somewhat like a lock fits a key. In this way only the correct substrate binds to the enzyme. CLIP Clip 2

    21. Induced fit model- the substrate induces the enzyme to change its shape. CLIP • Once the enzyme-substrate complex is together, the enzyme holds the substrate in a position where the reaction can occur. • Weak bonds form between the substrate and the amino acids in the active site. • Enzymes are not used up in the reaction

    22. Example of an enzyme-catalyzed reaction: Hydrolysis of sucrose A solution of sucrose dissolved in sterile water will sit for years at room temp with no appreciable hydrolysis occurring….BUT, if add SUCRASE (an enzyme), the sucrose will be converted in seconds…

    23. Functions: • All enzymes have four special features in common: • They do not make processes happen that would not take place on their own. They just make the processes take place faster! • 2. Enzymes are not permanently altered or used up in reactions. • 4 Each enzyme is highly selective about its substrate.

    24. Control, regulation and other points of Metabolism Enzymes: Control

    25. Physical and Chemical Environment affects Enzyme Activity… • Temperature– too high, denatures protein • Concentration of enzyme and substrate- • pH– too high or too low, denatures protein • Cofactors – inorganic(elemental) nonprotein helper bound to active site; must be present for some enzymes to function (zinc, iron, copper) • Coenzymes – organic nonprotein helper bound to active site; again, must be present (vitamins)-required for enzymes to work -make up a part of the active site --without the coenzyme, the enzyme will not function. Clip; Coenzymes

    26. How fast or slow the enzyme works depends on: 1. The concentration of the enzyme All necessary cofactors (inorganic molecules) and coenzymes (vitamins) are present above. 1. Presence of excess substrate, the reaction rate increases in direct proportion to the [enzyme]. 2.Rate increases until reaches max velocity.

    27. How fast or slow the enzyme works depends on • the concentration of the enzyme. If the enzyme is diluted, its concentration is lowered, which slows the reaction rate. • If the enzyme concentration remains constant as the substrate concentration increases, the rate of the reaction increases until the rate of reaction approaches the maximum velocity. • From this point on the enzyme is saturated and the rate of reaction can no longer increase.

    28. How fast or slow the enzyme works depends on 2. pH -different enzymes have different optimal pHs 3. Temperature -body temp

    29. ph can affect enzyme activity.

    30. Control of Metabolism • Cell regulates metabolic pathways by controlling when and where enzymes are active • Does this by *switching on or off the genes for production of specific enzymes OR *regulating enzymes after they are made

    31. Enzyme Inhibitors 2 types 1. Competitive blocks active site, mimics substrate 2. Noncompetitive bind to another part of enzyme and change shape of enzyme – can’t work on substrate

    32. Competitive Inhibition • Molecules that resemble the substrate compete for the active site. • Reduce the productivity of the enzyme by preventing the substrate from combining w/the enzyme. • Inhibitors can be reversible or irreversible. Animation

    33. Noncompetitive Inhibition • Enzyme contains more than 1 active site and the substrates do not resemble each other. • When one substrate binds to an active site, the second site is blocked. • Binding is random and a function of the concentration of each substrate.

    34. Allosteric Inhibition(type of Noncompetitive) • Two active sites, one for the substrate and one for an inhibitor (or enhancer). Usually reversiable. EX: Feedback inhibition during glycolysis. -ATP inhibits the enzyme PFK which catalyzes step 3. A metabolic pathway is switched off by its end product. Prevents the cell from wasting energy. Clip Clip 2 with Quiz

    35. Allosteric regulation of enzyme activity *By binding to allosteric site, can either inhibit or stimulate *Most allosterically regulated enzymes are made up of one or more polypeptide subunits

    36. Negative Feedback Inhibition: Swiching off of a metabolic pathway by its end product, which acts an an inhibitor of an enzyme within the pathway. PFK is also an example

    37. Positive Feedback: • The product of one or a series of enzymatic reactions acts upon the enzymes responsible for the generation of that product to increase the activity of one or more of these enzymes. Your stomach normally secretes a compound called pepsinogen that is an inactive enzyme. As your body converts pepsinogen to the enzyme pepsin, it triggers a process that helps convert other pepsinogen molecules to pepsin. This cascade effect occurs and soon your stomach has enough pepsin molecules to digest proteins Childbirth: The hormone oxytocin stimulates and enhances labor contractions. As the baby moves toward the birth canal, pressure receptors within the cervix send messages to the brain to produce oxytocin. Oxytocin travels to the uterus through the bloodstream, stimulating the muscles in the uterine wall to contract stronger. More pressure…more oxytocin is produced until the baby is outside the birth canal.

    38. Review: • Mr. Anderson’s “Enzymes” review •