Notes on Enzymes, Metabolic Diversity, and Microbial Growth

Introduction to Enzymes and Enzyme Structure

  • Enzymes: Biological catalysts that speed up reactions by lowering activation energy of the reaction.

    • Without enzymes, cellular reactions take too long, risking cell viability.

Structure of Enzymes

  • Enzymes are primarily proteins.

    • Inactive protein portion: Apoenzyme.

    • Active enzyme form: Holoenzyme, formed when an apoenzyme combines with necessary coenzymes and cofactors.

    • Coenzymes: Organic molecules, e.g., vitamins.

    • Cofactors: Inorganic molecules, e.g., calcium, iron.

Enzyme Mechanism

  • Substrate binding at the active site, analogous to a lock and key.

    • Catabolic reactions: Breaking down substrates into smaller products.

    • Anabolic reactions: Combining smaller substrates to form larger products.

Feedback Loops in Homeostasis

  • Positive Feedback Loop:

    • Accelerates processes until a defined goal is reached (e.g., childbirth with oxytocin stimulating contractions).

  • Negative Feedback Loop:

    • Regulates processes to maintain equilibrium (e.g., thermostat system).

Inhibition of Enzyme Activity

  • Types of Inhibition:

    • Competitive Inhibition:

    • Inhibitors bind to active site, blocking substrate binding (analogy: person blocking a desk).

    • Noncompetitive Inhibition:

    • Inhibitors bind to the allosteric site, changing active site shape (analogy: a changed lock that no longer accepts the key).

Metabolic Diversity

Definitions

  • Autotrophs: Organisms that produce their own food using inorganic sources, e.g., carbon dioxide.

  • Heterotrophs: Organisms that rely on existing organic sources for nutrients, e.g., glucose.

Energy Sources

  • Phototrophs: Convert light energy into ATP (via photosynthesis).

  • Chemotrophs: Obtain energy by breaking down chemicals.

    • Divided into:

    • Chemolithotrophs: Use inorganic chemicals.

    • Chemoorganotrophs: Use organic chemicals.

Groups Based on Metabolism

  • Photoautotrophs: Light for energy and inorganic sources for carbon.

  • Photoheterotrophs: Light for energy and organic sources for carbon.

  • Chemolithoautotrophs: Inorganic sources for energy and carbon.

  • Chemoorganoheterotrophs: Organic sources for energy and carbon.

Microbial Growth

Overview

  • Focus on prokaryotic growth (bacteria, archaea).

  • Bacteria reproduce by binary fission (one cell splits into two).

Key Terms

  • Generation Time: Time needed for one reproductive cycle (short for microbes, often minutes).

  • Doubling Time: Time needed for population to double.

Population Calculation

  • Formula: n<em>t=n</em>o×2nn<em>t = n</em>o \times 2^n

    • $n_t$: population at a given time.

    • $n_o$: original population.

    • $n$: number of generations (time passed / generation time).

Environmental Influences on Growth

Temperature

  • Temperature ranges:

    • Survival Range: Range organisms can survive but not grow.

    • Growth Range: Range where organisms actively grow.

    • Optimal Growth Range: Ideal temperature for maximum efficiency.

  • Groups Based on Temperature Preferences:

    • Psychrophiles:

    • Growth range: -5ºC to 15ºC (cold environments).

    • Psychrotrophs:

    • Growth range: 20ºC to 30ºC (cooler temperatures).

    • Mesophiles:

    • Growth range: 25ºC to 45ºC (includes human pathogens).

    • Thermophiles:

    • Growth range: 45ºC to 70ºC (hot springs).

    • Hyperthermophiles:

    • Growth range: 70ºC to 110ºC (extreme environments like thermal vents).

Oxygen Requirements

  • Types of organisms based on oxygen usage:

    • Obligate Aerobes: Require oxygen.

    • Obligate Anaerobes: Require absence of oxygen.

    • Facultative Anaerobes: Can grow with or without oxygen.

    • Microaerophiles: Require low oxygen concentrations.

    • Aerotolerant Anaerobes: Tolerate oxygen, but don’t use it for growth.

pH Tolerance

  • Neutrophiles: Prefer near neutral pH (around 7).

  • Acidophiles: Prefer acidic environments (pH < 5.5).

  • Alkaliphiles: Prefer alkaline environments (pH > 8.5).

Water Requirements

  • All living things require water; halophiles can survive in high salt environments but must avoid plasmolysis (loss of water due to external high solute concentrations).

Chemical and Nutritional Requirements

Major Elements

  • Essential in high quantities: Carbon, hydrogen, oxygen, nitrogen, sulfur, phosphorus, potassium, calcium, and trace elements.

Growth Factors

  • Substances needed by cells that they cannot synthesize and must obtain from the environment.

  • Implications for microbial growth control.

Nutritional Concerns and More

  • Atmospheric Requirements: Influence microbial growth. Examples include capnophiles (high CO2 environments) and methanogens (methane producers).

Growth Curves in Cultures

Types of Cultures

  • Continuous Culture: Continuous supply of nutrients, population growth seen as exponential.

  • Batch Culture: Limited nutrients, population phases:

    • Lag Phase: Initial adjustment period.

    • Log Phase: Exponential growth phase.

    • Stationary Phase: Balance between growth and death rates.

    • Death Phase: Decline of population over time (prolonged decline may return resources).

Controlling Microbial Growth

  • Sidle vs. Static:

    • Sidle: Kills microbes (e.g., bactericide).

    • Static: Prevents growth (e.g., bacteriostatic).

Considerations for Control Methods

  • Type of microbe, microbial population size, environmental factors, risk of infection.

  • Control methods: Physical (heat, filtration) and chemical (antiseptics, disinfectants).

Methods of Action

  • Alteration of Membrane Permeability: Disruption of cell membranes prevents nutrient uptake.

  • Damage to Proteins and Nucleic Acids: Inhibition of essential cellular processes leads to cell death.

Physical Control Methods

Heat

  • Moist Heat: Denaturation of proteins.

  • Dry Heat: Oxidation of cellular components.

  • Thermal Death Point/Time: Evaluative temperatures and times needed for organism sterilization.

Filtration

  • Physical removal of microbes.

Cold and Desiccation

  • Primarily static methods; inhibit growth.

Radiation

  • Ionizing and non-ionizing radiation as killers.

Chemical Control Methods

Phenols and Derivatives

  • Disrupt cell membranes and denature proteins.

Quaternary Ammonium Compounds

  • Membrane disruption, effective against gram-positive bacteria.

Antibiotics and Antimicrobial Drugs

Antibiotic Definition

  • Antimicrobial substances produced by living organisms, effective primarily against bacteria.

Spectrum of Activity

  • Narrow-spectrum vs. broad-spectrum antibiotics.

  • Examples of antibiotics based on effectiveness against different groups (tetracycline vs. penicillin).

Modes of Action

  • Five primary actions including inhibition of cell wall synthesis and protein synthesis, nucleic acid synthesis injury, plasma membrane injury, and central metabolite synthesis inhibition.

Mechanisms of Resistance

  • Genetic mutation, plasmid transfer, population shift, and four main resistance mechanisms (blocking entry, inactivation, alteration of target molecule, and efflux).

Safety Considerations

  • Allergic reactions, drug interactions, potential damage to host cells, and importance of maintaining normal flora.

Conclusion

  • Summary of key concepts related to enzymes, microbial growth, and control methods.

  • Next week will discuss antibiotics and their effects on microbial life.