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Microbiology. Chapter 8. Part I. Enzymes. Enzymes Catalyze Chemical Reactions of Life. Increase reaction rates without being consumed by the reaction Lower the activation energy Active site is where the substrate binds Active site is where chemistry happens

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Chapter 8

Part i

Part I


Enzymes catalyze chemical reactions of life
Enzymes Catalyze Chemical Reactions of Life

  • Increase reaction rates without being consumed by the reaction

  • Lower the activation energy

  • Active site is where the substrate binds

  • Active site is where chemistry happens

    • Chemistry is performed by side chains of amino acids

    • Cofactors or coenzymes

  • Active site has specificity

Reaction coordinate
Reaction Coordinate

  • Description of energy changes during the reaction

  • Horizontal axis is charts the progessive chemical changes (bond breakage/bond formation) as S is converted into P

  • Vertical axis represents Energy

  • Transition state – not a reaction intermediate

    • Fleeting molecular moment in which bond breakage, bond formation are happening

Reaction coordinate1
Reaction Coordinate

∆G’º = -RTlnK’eq

Just because delta G is favorable

does not mean that the reaction is


Enzyme terminology
Enzyme Terminology

  • Holoenzyme

    • Is a combination of protein (apoenzyme) and one or more cofactors

  • Cofactors

    • Coenzyme – complex organic molecules

    • Metal ions

Enzyme structure
Enzyme Structure

  • Holoenzyme

    • Apoenzyme – protein

    • Cofactors – complex organic molecules

    • Coenzyme – metal ions

  • Active site usually contains the cofactors and coenzymes because they are crucial for the chemistry

Enzyme substrate interactions
Enzyme Substrate Interactions

  • Specificity of active site – induced fit

  • Bonds between substrate and enzyme are weak and reversible

  • Once the enzyme substrate complex has formed chemical reactions occur on the substrate and the product is released

  • Most enzyme reactions are reversible with the exception of enzymes which regulate metabolic pathways

Enzymes in disease
Enzymes in Disease

  • Virulence Factors

  • Enzymes that are excreted from microorganisms that contribute to the pathogenicity of diseases

Virulence factors
Virulence Factors

  • Streptococcus pyogenes – throat and skin infections

    • Streptokinase – digests blood clots and assists in wound invasion

  • Pseudomonas aeruginose – respiratory and skin pathogen

    • Elastase and collagenase digestive enzymes

  • Clostridium perfringens – gas gangrene

    • Lecithinase C lipase damages cell membranes; therefore massive tissue death

Virulence factors1
Virulence Factors

  • Not all virulence factors secrete enzymes which digest tissues

  • Can protect microbes from effects of drug therapy

  • Penicillinase

    • Inactivates penicillin

Enzymes and their environment
Enzymes and Their Environment

  • Why do you think enzymes only function properly under established conditions of pH, temperature

  • Why do you think agents such as heavy metals and alcohol also have the ability to denature enzymes

  • Take a look at enzyme structure

Part ii

Part II


Metabolism in microbes
Metabolism In Microbes

  • All chemical reactions of a cell

  • Two general classes

    • Anabolism or biosynthesis

    • Catabolism or degradative reactions

Metabolic pathways
Metabolic Pathways

  • The product of one reaction is often the substrate for the next

  • Every pathway has one or more regulatory enzymes

  • All other enzymes in the pathway usually are not regulated

    • They operate whenever the substrate is available

Cell energetics
Cell Energetics

  • Not all cellular reactions are equal with respect to energy

  • Exergonic – Energy Released

  • Endergonic – Energy Requiring

Structure of fad and nad
Structure of FAD and NAD+

  • Both are electron carriers in the ETC

What is the purpose of nadh
What is the purpose of NADH

  • The electron transport chain transfers electrons from NADH to other electron carriers

  • The electrons end up on various molecules

  • However, electron movement is associated with making a proton gradient

  • Proton gradient is responsible for ATP production


  • How could you uncouple the ETC from the production of ATP

  • What if you treated a cell with a weak hydophobic acid such as FCCP or DNP

Aerobic respiration
Aerobic Respiration

  • Characteristic of many bacteria, fungi, protozoa, and animals

  • Electrons and hydrogen are taken from highly reduced, high energy compounds

  • Electrons and hydrogen end up on O2 to form H20

  • Much ATP is made

Nutrient processing
Nutrient Processing

  • Extremely varied in bacteria

  • Remember Microbes are classified according to their O2 requirements

    • Aerobic respiration

    • Anaerobic respiration

    • Fermentation

Anaerobic respiration
Anaerobic Respiration

  • System involves the same three pathways as aerobic respiration

  • Final electron acceptor is not 02 but instead NO3-, SO4-, CO3-

Other fates of pyruvate
Other Fates of Pyruvate

  • Fermentation products can be grouped into two general categories

  • Alcoholic fermentation

  • Acidic fermentation


Alcoholic fermentation

Homolactic acid fermentation

Other energy sources
Other Energy Sources

  • Glucose is a major source of energy

  • However, for any other organic substance usually there exists a microorganism that can degrade that substance for energy

  • Fats

  • Proteins

  • Any other organic molecule