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Enzymes. Large bio-molecules that increase the rate of reaction in living systems Enzymes act as catalyst – molecules that speed up a chemical reaction.

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Presentation on theme: "Enzymes. Large bio-molecules that increase the rate of reaction in living systems Enzymes act as catalyst – molecules that speed up a chemical reaction."— Presentation transcript:

1 Enzymes

2 Large bio-molecules that increase the rate of reaction in living systems Enzymes act as catalyst – molecules that speed up a chemical reaction by lowering the activation energy

3 Enzymes –Most Enzymes are globular protein molecules –Other types such as ribozymes are common –Extremely effective causing reactions to be 10 9 to times faster –Extremely specific - each reaction catalyzed by only 1 enzyme e.g. Trypsin: cleaves peptide linkages only on carboxyl side of lysine and arginine Many enzymes are stereospecific: Arginase converts L-arginine to to L-ornithine but does not convert D-arginine

4 Enzymes There are more than 3000 enzyme in a cell Enzymes are distributed in the body relative to their need (digestive enzymes in stomach and pancreas) From Yahoo Images

5 Enzyme Nomenclature Enzymes are typically given names based on the reactions they are involved in with most ending in …… ase –Lactate dehydrogenase speeds up removal of H from lactate –Acid phosphatase cleaves phosphate ester bonds under acidic conditions (some older ones do not end in “ase” like pepsin, trypsin, chymotrypsin)

6 Enzymes are classified into six major groups according to their reactions –1. Oxidoreductases catalyze oxidations and reductions –2. Transferases catalyze NH 2, CH 3, etc. from one molecule to another –3. Hydrolases catalyze hydrolysis reactions –4. Lyases catalyze addition of two group to make C=C or removes two atoms to create C=C –5. Isomerases catalyze isomerization reactions –6. Ligases or Synthetases catalyze joining of two molecules

7 Enzyme - Youtube hI13ghttp://www.youtube.com/watch?v=AFbPHl hI13g

8 Enzyme Terms Most enzymes are made of just a Polypeptide chain Some enzymes have a nonprotein portion called a cofactor The protein portion is called an apoenzyme Cofactors = nonprotein portions = coenzyme –Metal Cofactors such as Zn 2+, Mg 2+ –an apoenzyme cannot catalyze a reaction withouth its cofactor

9 Enzyme Terms Substrate = compound on which the enzyme “works” Active site = specific portion of the enzyme where substrate binds

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11 Enzyme Terms Activation = process that makes an inactive enzyme active Inhibition = any process that makes an enzyme less active or inactive –competitive vs. noncompetitive inhibition

12 Enzyme Activity Enzyme and substrate concentration rate Enzyme concentration

13 Enzyme Activity Enzyme and substrate concentration rate Substrate concentration maximum rate (enzyme saturation)

14 Enzyme Activity Temperature – changes conformation rate Temperature 37 o C

15 Temp Effect - youtube MGA

16 Enzyme Activity pH – changes conformation or denatures rate pHbasicacidic 5.3

17 Denaturation - pH 8PFb9dOR8c

18 Mechanism Mechanism of Enzyme Activity –Highly specific –Enzyme-Substrate Complex –Lock and Key Model rigid 3-D structure fits exactly into active site active site may have only 1 or 2 AA, enzyme may have hundreds!

19 Mechanism Mechanism of Enzyme Activity –Induced Fit Model Daniel Koshland some flexibility shape changes to fit substrate hand and glove analogy

20 Inhibitors Competitive Inhibition –Inhibitor molecule takes the active site –Substrate cannot react at active site –Large concentrations of substrate “overcome” inhibition (competitive) Something that inhibits the enzymes ability to react

21 Inhibitors Noncompetitive Inhibition –Inhibitor molecule takes other than the active site –Enzyme structure is changed - active site is altered –Large concentrations of substrate do NOT change inhibition (noncompetitive) Something that inhibits the enzymes ability to react

22 Inhibitors Inhibition rate Substrate concentration No inhibitor Competitive Inhibitor Noncompetitive Inhibitor

23 Enzyme inhibition - youtube JN3T8

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25 Chemical Connections page 592

26 Enzyme Regulation Feedback Control –Regulation by environmental control –One enzyme may control the activity of another! ABCD E1E1 E2E2 E3E3 Product D may inhibit E 1

27 Enzyme Regulation Proenzymes –Enzymes manufactured may need a small polypeptide removed to become active –Also called zymogens –Example: trypsin is synthesized as trypsinogen trypsinogen is the inactive form once in the digestive tract it is converted to trypsin

28 Enzyme Regulation Allosterism –regulation at site other than active site regulatory siteregulatory site –active site changes and becomes more or less reactive positive modulation negative modulation regulator –“regulator” “Thus the allosteric enzyme is controlled by the regulator.”

29 Enzyme Regulation Isoenzymes Same enzyme, but different form, in different tissues: –Lactate dehydrogenase (4 subunits) made from two different types – H and M –H 4 predominates in heart –M 4 predominates in liver and skeletal muscle

30 Medical Diagnosis Most enzymes are confined to cells Small amount can be found in blood, urine, etc. Analysis of body fluids can help diagnose disease or injury (enzymes spilled to serum) E.g. Heart Attack (???) --- check serum levels: –AST aspartate aminotransferase –LD-Plactate dehydrogenase –CKcreatine kinase

31 Medical Diagnosis Enzyme NormalFluidDisease alanine aminotransferase (ALT)3-17 U/LserumHepatitis acid phosphatase serumProstate cancer alkaline phosphatase (ALP)13-38serumLiver/bone disease amylase19-80serumPancreatic disease or mumps aspartate aminotransferase (AST)7-19serumHeart attack or hepatitis 7-49CSF lactate dehydrogenase (LD-P) serumHeart attack creatine kinase (CK)7-60serumHeart attack phosphohexose isomerase (PHI)15-75serumHeart attack


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