Enzymes continued

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Enzymes continued

• Some enzymes work together to complete a series
  of reactions to produce a given product
• A B -------? C -------? D ------------? E
• Collectively, these steps are known as a
  metabolic pathway

Enzyme 1
Enzyme 2
Enzyme 3
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A metabolic pathway
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The entire set of all chemical reactions being
performed by an organism is called its metabolism

• Anabolism chemical reactions that expend energy
  to make or transform chemical bonds
• Catabolism chemical reactions that harvest
  energy by breaking chemical bonds

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Catabolism involves exergonic reactions
Anabolism involves endergonic reactions
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Control of Metabolism

• Coenzymes
• Inhibitors
• Allosteric regulation
• Feedback Inhibition
• Cooperativity

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Coenzymes

• Coenzymes are bound at the active site in order
  to interact with the substrate and play an
  essential role in the catalysed reaction.
• They act as carriers of a variety of chemical
  groups. .

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Most water-soluble vitamins are components of
coenzymes
Vitamin Coenzyme Deficiency
Thiamine (B1) Thiamine pyrophosphate Beriberi (weight loss,other problems
Riboflavin (B2) FAD Mouth lesions, dermatitis
Nicotinic acid (niacine) NAD Pellagra (dermatitis, depression)
Pantohtinic acid Coenzyme A Hypertension
Biotin Biotin Rash, muscle pain
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Inhibitors

• Specific for an enzyme
• Can be reversible or non-reversible
• Competitive inhibitors
• Non-competitive inhibitors

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Competitive vs. Non-competitive inhibitors
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Many inhibitors are used as pesticides or drugs
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Regulating the rates of enzyme-driven reactions

• Cells use inhibitors and activators to turn off
  and on enzymes
• Many enzymes are controlled by an allosteric site
  remote from the active site

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Allosteric regulation of enzyme activity
Many allosterically controlled enzymse show
quaternary structure
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Feedback inhibition
Many enzymes are actually regulated by the end
products of the reaction they catalyze
Enzyme 1
Enzyme 2
Enzyme 3
Inter- mediate
Inter- mediate
Start of pathway
X
Product
Presence of product inhibits enzyme 1
This prevents too much product from being made
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An example of Feedback inhibition