Microbial Metabolism

Metabolism: Energy and Enzymes

METABOLISM

From the Greek term, metaballein, meaning change.Pertains to all chemical reactions and physical workings of the cell.

Energy

Defined as the capacity to do work or to cause particular changes.Cellular metabolism – the totality of all chemical reactions that a cell carries out.Metabolism- obtain energy and materials for growth.

ATP

Is the central chemical in the energy transformations of cellular metabolismATP cannot be stored for long periods of time so it must be continually made.

Role of Enzymes

Cellular metabolism is based on chemical reactions catalyzed by enzymes.Enzymes are biological catalysts – accelerate the rates of chemical reactions.Most are proteins but a very few are RNA.

ENZYMES

How do they work???

Enzymes

Increase rates of a cell’s chemical reactions by more than a million times.Energy is required for a chemical reaction to occur. Enzymes lower activation energy.

Energy of Activation

Increasing thermal energy (heating), which increases molecular velocityIncreasing the concentration of reactants, orAdding a catalyst

Enzymes

Exhibit high degree of substrate specificity.The enzymes a particular cell synthesizes will determine which chemical reactions occur in cellular metabolism of that cell.Substrate + E E-S complex E + Product

Enzyme Structure

Enzymes can be classified as simple or conjugated.Simple – consist of protein aloneConjugated – protein + nonprotein

Enzyme Anatomy

Active SiteAllosteric SiteCo enzymeCofactorApoenzymeHoloenzyme

Prosthetic Groups

Active Site

Competitive Inhibition

Apoenzyme: Specificity and the Active Site

Range in sizeExhibit levels of molecular complexity

Enzyme Specificity

The apoenzyme of each enzyme differs from others in its primary structureNuances in polypeptide folding Surface features of the tertiary structure provide a unique and specific site

Coenzymes

Activities many and variedVitamins

Classification of Enzyme Function

Site of actionType of action Type of substrate

Location & Regularity of Enzyme Action

Exoenzymes – ex. Penicillinase, lipase, proteasesEndoenzymes – ex. Metabolic pathway enzymes

Enzymes

ConstitutiveInduced

Synthesis & Hydrolysis Reactions

Bacterial cells are constantly in a frenzy of activity, constantly synthesizing proteins, DNA, and RNA.Anabolic Reactions – Condensation ReactionsRequire ATPCatabolic Reactions – Hydrolysis Reactions

Transfer Reactions by Enzymes

Addition or removal of a functional group are important to the overall economy of the cell.Oxidation – Reduction reactions

Important in metabolic pathwaysRole in molecular conversions

The Role of Microbial Enzymes in Disease

Exoenzymes which help bacteria avoid host defenses or promote their multiplication in tissues.Virulence factors or toxins: Streptococcus pyogenes (streptokinase, protease); Staphylococcus aureus (lipases); Pseudomonas aeruginosa (elastase, collangenase)

The Role of Microbial Enzymes in Disease

Clostridium perfringens (lecithinase C, lipase)

The Sensitivity of Enzymes to their Environment

Activity of an enzyme is influenced by the cell’s environment.Temperature, pH, osmotic pressureDenaturation – disruption causes distortion of the enzyme

Checklist

Act as organic catalysts to speed up the rate of cellular reactionsAre composed of protein and may require cofactorsHave unique characteristics such as shape, specificity, and functionEnable metabolic reactions to proceed at a speed compatible with life

Checklist

Provide a reactive site for target molecules called substratesAssociate closely with substrates but do not become integrated into the reaction productsAre not used up or permanently changed by the reaction

Checklist

Lower the activation energy required for a chemical reaction to proceedCan be recycled, thus function in extremely low concentrationsAre limited by particular conditions of temperature and pH

Metabolic Pathways and Carbon Flow

The enzymatically mediated metabolic reactions of a cell proceed via a series of small discrete steps that establish a metabolic pathway.CatabolicAnabolic

Metabolic Pathways

Rarely consist of a single action or step.Each step catalyzed by an enzyme.Pathways are interconnected and merge at different sites.Pacemakers – sets the rate of a pathway’s progression.Respond to various control signals

Direct Controls

Competitive InhibitionFeedback ControlNegative Feedback

Controls on Enzyme Synthesis

Enzyme RepressionEnzyme Induction

The Pursuit and Utilization of Energy

Biosynthesis, movement, transport, or growth could proceed without ENERGY

Nutritional Patterns Among Bacteria

Two criteria: Energy (E) source & Carbon (C ) SourcePrototrophs – light as primary E sourceChemotrophs – redox reactions for EAutotrophs – use CO2

Heterotrophs – require an organic C source

Classification

PhotoautotrophsPhotoheterotrophsChemoautotrophsChemoheterotrophs