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Understanding Enzymes: Catalysts for Chemical Reactions

Enzymes are proteins that act as catalysts, accelerating reactions without being permanently changed. They have specificity for their substrates and work by weakening chemical bonds, lowering activation energy. Enzyme activity is affected by environmental conditions, cofactors and coenzymes, and enzyme inhibitors.

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Understanding Enzymes: Catalysts for Chemical Reactions

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  1. Enzymes

  2. What Are Enzymes? • Most enzymes are proteins • Act as catalysts to accelerate a reaction • Not permanently changed in the process • Can be reused

  3. Enzyme specificity • Are specific for what they will catalyze • Arereusable • End in –ase -Sucrase -Lactase -Maltase

  4. How do enzymes work? Enzymes work by weakening chemical bonds of the reactant, which lowers activation energy(energy needed to start the reaction)

  5. How do enzymes work?

  6. Substrates Enzyme The substance (reactant) an enzyme acts on is the substrate Binds Substrate

  7. Enzyme Active Site • A restricted regionof an enzyme molecule which binds to the substrate. Substrate Enzyme + Substrate = ENZYME-SUBSTRATE COMPLEX Active Site

  8. How Does a Substrate Fit With Its Enzyme? TWO MODELS: 1.) Lock-and-Key Model 2.) Induced Fit Model

  9. Lock-and-Key MODEL • Active Sites are SPECIFIC and COMPLEMENTARY for their substrates • This is like a LOCK & KEY Idea of “One substrate for one enzyme”

  10. Induced Fit • A change in the shape (configuration) of an enzyme’s active site • Inducedby the substrate Idea that “One enzyme can have more than one substrate”

  11. What Affects Enzyme Activity? THREE FACTORS: 1. Environmental Conditions (temperature, pH, ionic concentration) 2. Cofactors and Coenzymes 3. Enzyme Inhibitors

  12. Environmental Conditions 1. Extremetemperatures are the most dangerous - High fevers 2. pH (most like 6 - 8 pH; near neutral) 3. Ionic concentration (salt ions & salinity) ALL OF THESE FACTORS DISRUPT THE SHAPE OF THE ENZYME, SO IT WILL UNFOLD (DENATURE)

  13. Cofactors and Coenzymes 1. Metal ions (zinc, iron) = Cofactors (nonorganic) 2. Vitamins (biotin, B12) = Coenzymes (organic) • Sometimes needed for proper enzymatic activity…help to further speed up the reaction • Example: NAD+, a coenzyme composed of niacin, transfers electrons to enzymes during cell respiration

  14. Enzyme Inhibitors: 1st Type 1.Competitive Inhibitors: Chemicals that resemblean enzyme’s normal substrate and compete with it for the active site. Ex: Penicillin

  15. 2. Noncompetitive Inhibitors:Inhibitors that do not enter the active site but bind to another part of the enzyme causing the enzyme to change shape, which in turn alters the active site’s shape. active site altered Enzyme Inhibitors: 2nd Type Ex: Cyanide

  16. Most are PROTEINS Act as CATALYSTS  ACTIVATION ENERGY SPEED  Reactions Provide an ACTIVE SITEto bind to its substrate and form an enzyme-substrate complex The two models are LOCK AND KEYand INDUCED FIT Are REUSABLE(after converting a reactant to product, can do this multiple times!) ENZYMES: KEY POINTS

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