The Metabolism of Microbes
- Metabolism: general term for all chemical reactions and physical workings of the cell.
- Anabolism (or biosynthesis): process that results in synthesis of cell molecules and structures.
- Catabolism: opposite or compliment of anabolism, they break bonds and often produce energy.
- Metabolites: compounds given off by the complex networks of metabolism.
- Enzymes: Catalyzing the Chemical Reactions of Life
- Enzymes are catalysts, increase the rate of chemical reaction with being part of the reaction.
- Energy of activation: amount of energy required to initiate bonds to bond or break.
- Substrate: reactant molecules.
- Enzyme is larger than the substrate.
- Enzyme structure
- Simple enzymes: consist of just protein.
- Conjugate enzymes: consist of protein and non-protein.
- Also referred to as haloenzyme.
- The protein is called the apoenzyme and non-protein molecules are called cofactors.
- Cofactors: organic molecules, also known as coenzymes.
- Help perform alterations to active site.
- Apoenzymes: Specificity and the Active Site
- Active site (or catalytic site): location the substrate binds.
- Induced fit: enzyme slightly adjusting shape to better fit the substrate.
- Cofactors: Supporting the Work of Enzymes
- Metallic cofactors: metals that participate in precise functions between the enzyme and its substrate.
- Metals help bring the substrate and the active site closer together.
- Participate directly in chemical reactions with enzyme-substrate complex.
- General function of coenzyme is to remove functional group from one substrate and add it to another.
- One of the the most important components of coenzymes are vitamins.
Classification of the Enzyme Functions
- Location and Regularity of Enzyme Action
- Exoenzymes: enzymes that are transported extracellularly.
- Endoenzymes: enzymes that are retained intracellularly and function there.
- Constitutive enzymes: enzymes always present and in relatively constant amounts regardless of the amount of substrate.
- Ex: proteins involved in utilizing glucose.
- Induced enzyme: enzyme not constantly present and is produced only when its substrate is present.
- Synthesis and Hydrolysis Reactions
- Condensation reactions: anabolic reactions that require enzymes to form covalent bonds between smaller substrate molecules.
- Usually require ATP and release one water molecule.
- Hydrolysis reaction: breaking of bonds that requires water to be an input.
- Transfer Reactions by Enzymes
- Oxidation and Reduction
- Oxidation: loss of electrons.
- Reduction: gain of electrons.
- Some enzymes add or remove functional groups from substrates to substrates.
- The Role of Microbial Enzymes in Disease
- Some microbes use enzymes to avoid host defenses or promote their multiplication in tissues.
- Some use enzymes to cause tissue damage.
- Sensitivity of Enzymes to Their Environment
- In general enzymes operate in natural temperature, pH, and osmotic pressure of an organisms habitat.
- Labile: chemically unstable.
- Low temperature: catalysis.
- High temp: denaturation.
Regulation of Enzymatic Activity and Metabolic Pathways
- Pathways are often a linear path where one product is a reactant (substrate) for another.
- Direct Controls on the Actions of Enzymes
- Competitive Inhibition
- Molecules with similar structures as normal substrates can occupy the active site.
- Molecular blocks further activity of the enzyme.
- Feedback Control
- Negative feedback: product fed back to system and cancels an enzyme's activity.
- Allosteric enyzmes have an additional regulatory site for other molecules besides the substrate which causes a shift of the active site to be distorted and no longer bind to its substrate.
- Feedback inhibition: allosteric inhibitors that can temporarily stop the action of the enzyme.
- When at some point the end product is used up and more of it is needed, the enzyme will be released from inhibition and resume catalysis.
- Controls of Enzyme Synthesis
- Enzyme repression: means to to stop further synthesis of an enzyme somewhere along its pathway.
- Excess products can cause the genetic apparatus responsible for the enzyme to automatically be suppressed.
- Enzyme induction: enzymes appear only when suitable substrates are present; synthesis of enzyme is enzyme is induced by its substrate.
The Pursuit and Utilization of Energy
- Energy: capacity to do work or cause change.
- Exergonic: release of energy as it goes forward.
- Endogonic: addition of energy drives a reaction forward.
- Redox reactions: reaction of electron donors and receptors.
- Phosphorylate: add an inorganic phosphate to ADP or other compound.
- Dehydrogenation: removal of hydrogens.
Two Types of Metabolism
- Metabolism: sum total of all chemical reactions & physical working occurring in a cell.
- Catabolism of Other Substances
- Polysaccharides (CHO) --> [hydrolysis] --> Monosaccharides --> [glycolysis]
- Lipids --> [hydrolysis] --> Glycerol + Fatty Acids (hydrocarbons; lots of energy)
- Glycerol --> [glycolysis]
- Fatty Acids --> [Boxidation] -->Two Carbon Fragments (Acetyle CoA) --> [Kreb's Cycle]
- Protein --> [hydrolysis] --> Amino Acids (contain amino group, NH3) --> [Deanimation] --> Carboxylic Acid --> [Kreb's Cycle]
- Anabolism
- Photosynthesis
- 6CO2 + 6H2O + Energy --> C6H12O6 + 6O2