Chapter 8

Microbial Metabolism

Anabolism

Synthesis of cell products

Requires energy

Breakdown of large molecules into smaller ones

Releases energy

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Enzymes

All biochemical reactions need the presence of a specific and special class of proteins called enzymes

Properties of enzymes

Become physically attached to substrate

Participate in bonding

Do not become part of its products

Not used up by the chemical reaction

Can function over and over again

 

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Energy of activation

Minimum energy input necessary for reactants to form products in a chemical reaction

Less if enzyme is present

More if enzyme is absent or in low concentration

Types of enzymes

Simple

Protein alone

Conjugated or holoenzyme (Fig. 8.3)

Protein (apoenzyme) + non-protein (organic/inorganic cofactors)

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Apoenzyme

Apoenzyme is the protein part of an enzyme

Short (100 amino acids) to very long chains (10⁶ amino acids)

Molecular complexity (1-2-3-4-type of organization)

Unique active or catalytic sites for substrates to fit

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Coenzymes

Complex organic molecules, several of which are derived from vitamins (e.g. nicotinamide, riboflavin)

A deficiency in vitamins will prevent formation of holoenzymes affecting metabolism

NAD = nicotinamide adenine dinucleotide

FAD = flavin adenine dinucleotide

Role of coenzymes

Carrier of functional groups {CO₂, (NH₃⁺ = amino group NH₂), and others}

Work with apoenzyme to perform necessary alterations in a substrate

Removal of functional groups

Serve as transient carriers of specific atoms or functional groups during metabolic reactions

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Cofactors

These enzyme accessories can be

Organic such as coenzymes

Inorganic, such as Fe₂⁺, Mn₂⁺, or Zn₂⁺ ions

Metals participate in precise functions between the enzyme and the substrate

Role of cofactors

Activate enzymes

Help bring the active site and substrate close together

Participate directly in chemical reactions with the enzyme-substrate complex

Active or catalytic site

Specific region where the substrate binds to the apoenzyme

Site for reaction catalysis

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Steps involved in a chemical reaction

Enzyme fits substrate at the active site and forms a complex

Bonds are formed between enzyme and substrate

Reactions occur on the substrate

Cofactor aids in the reactions

Product is formed and released

Enzyme attaches to another substrate molecule

Cycle is repeated

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Textbook: Foundations in Microbiology. K.Park Talaro. 6th edition. McGraw Hill.

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