Biochemical Reaction Mechanisms

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Biochemical Reaction Mechanisms

• 1. Mechanism of action of a-chymotrypsin
• 2. Glycolysis metabolism of glucose
• 3. Biosynthesis of steroids from squalene

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Mechanism of action ofa-chymotrypsin

• (An enzyme that hydrolyzes peptides in the
  digestive system)

3
Catalytic triad Asp102, His 57, Ser 195
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a-chymotrypsin mechanism
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a-chymotrypsin mechanism
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Glycolysis

• Metabolism of glucose to form pyruvate and ATP

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Glycolysis converts glucose into two pyruvate
molecules

• with the production of 2 ATPs (high energy
  storage in cells)
• Isomerization of glucose to fructose
• Formation of iminium ion retro aldol to form two
  3-carbon sugars (as phosphates)
• Isomerization of dihydroxyacetone to
  glyceraldehyde (as phosphates)
• Oxidation, isomerization, dehydration and
  dephosphorylation to form pyruvate and ATP

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Isomerization of glucose to fructose
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Iminium ion retro aldol addition
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Isomerization to glyceraldehyde
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Oxidation, isomerization and dephosphorylation
(ATP forming)
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Biosynthesis of Steroids from Squalene
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Squalene (a shark oil terpene)
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Epoxidation of Squalene
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Acid-Catalyzed Epoxide Ring Opening A Ring
Formation
A
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Reaction of Alkene with Carbocation B Ring
A
B
A
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Cyclization to form C Ring
B
A
C
A
B
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Cyclization to form D Ring
C
D
A
B
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Hydride and Methyl Shifts
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Eventually...Cholesterol !
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Grading / Final Exam
Example

• You may replace any of the 5 tests by an
  improved grade on that section of the Exam.
• Only the higher grade counts.
• You need not retake a section if you are happy
  with your grade on that test.
• Everyone must take Section 6 (Ch 25, 26, 27 29)
  plus Section 7 (comprehensive mostly synthesis)

Your (best) score on these seven sections
plus the sum of your gla scores determines your
grade.