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Presentation on theme: "Enzymes."— Presentation transcript:

1 Enzymes

2 Enzymes 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 109 to 1020 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 NH2, CH3, 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

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 Zn2+, Mg2+ 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


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
Enzyme concentration

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

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

15 Temp Effect - youtube

16 Enzyme Activity pH – changes conformation or denatures rate acidic pH
5.3 pH basic

17 Denaturation - pH

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

21 Inhibitors Noncompetitive Inhibition
Something that inhibits the enzymes ability to react 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)

22 Inhibitors Inhibition Substrate concentration No inhibitor
Competitive Inhibitor Noncompetitive Inhibitor

23 Enzyme inhibition - youtube


25 Chemical Connections page 592

26 Enzyme Regulation A B C D Feedback Control
Regulation by environmental control One enzyme may control the activity of another! A B C D E1 E2 E3 Product D may inhibit E1

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 site active site changes and becomes more or less reactive positive modulation negative modulation “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 H4 predominates in heart M4 predominates in liver and skeletal muscle

30 Medical Diagnosis AST aspartate aminotransferase
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-P lactate dehydrogenase CK creatine kinase

31 Medical Diagnosis Enzyme Normal Fluid Disease
alanine aminotransferase (ALT) 3-17 U/L serum Hepatitis acid phosphatase serum Prostate cancer alkaline phosphatase (ALP) serum Liver/bone disease amylase serum Pancreatic disease or mumps aspartate aminotransferase (AST) serum Heart attack or hepatitis 7-49 CSF lactate dehydrogenase (LD-P) serum Heart attack creatine kinase (CK) serum Heart attack phosphohexose isomerase (PHI) serum Heart attack

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