Microbial Metabolism, Growth, and Control: Study Notes for Exam II

Chapter 5: Microbial Metabolism

Metabolism: Anabolism and Catabolism

Metabolism refers to all the chemical reactions that occur within a living cell. These reactions are divided into two main categories:

• Anabolism: The synthesis of complex molecules from simpler ones, requiring energy input. Anabolic reactions are essential for cell growth and repair.

• Catabolism: The breakdown of complex molecules into simpler ones, releasing energy. Catabolic reactions provide the energy needed for cellular processes.

Example: The breakdown of glucose during glycolysis is a catabolic process, while the synthesis of proteins from amino acids is anabolic.

Role of ATP in Metabolism

Adenosine triphosphate (ATP) is the primary energy carrier in cells. It stores energy released from catabolic reactions and supplies it for anabolic reactions.

• ATP is generated by the phosphorylation of ADP (adenosine diphosphate).

• Energy is released when ATP is hydrolyzed to ADP and inorganic phosphate.

Equation:

$\mathrm{ATP} + \mathrm{H}_2\mathrm{O} \rightarrow \mathrm{ADP} + \mathrm{P}_i + \text{energy}$

Enzymes: Components and Function

Enzymes are biological catalysts that speed up chemical reactions without being consumed. Key components include:

• Substrate: The molecule upon which the enzyme acts.

• Active Site: The region on the enzyme where the substrate binds.

• Enzyme: The protein that facilitates the reaction.

Example: The enzyme hexokinase catalyzes the phosphorylation of glucose in glycolysis.

Factors Influencing Enzymatic Activity

• Temperature: Each enzyme has an optimal temperature; extreme temperatures can denature enzymes.

• pH: Enzymes function best at specific pH ranges.

• Substrate concentration: Increased substrate increases reaction rate up to a saturation point.

• Inhibitors: Chemicals that decrease enzyme activity (competitive and noncompetitive inhibitors).

Oxidation and Reduction (Redox Reactions)

Redox reactions involve the transfer of electrons between molecules:

• Oxidation: Loss of electrons.

• Reduction: Gain of electrons.

These reactions are essential for energy production in cells.

Electron Transport Chain (ETC) and Chemiosmosis

The ETC is a series of protein complexes in the cell membrane (prokaryotes) or mitochondria (eukaryotes) that transfer electrons and pump protons to generate a proton gradient.

• Chemiosmosis: The movement of protons back across the membrane through ATP synthase, driving ATP production.

Equation:

$\mathrm{NADH} + \mathrm{H}^+ + 1/2\,\mathrm{O}_2 \rightarrow \mathrm{NAD}^+ + \mathrm{H}_2\mathrm{O}$

Glycolysis

Glycolysis is the metabolic pathway that converts glucose into pyruvate, producing ATP and NADH.

• Occurs in the cytoplasm.

• Net gain: 2 ATP and 2 NADH per glucose molecule.

Aerobic and Anaerobic Respiration

• Aerobic respiration: Uses oxygen as the final electron acceptor; produces the most ATP.

• Anaerobic respiration: Uses other inorganic molecules (e.g., nitrate, sulfate) as final electron acceptors; yields less ATP.

Fermentation

Fermentation is an anaerobic process that allows ATP production without an electron transport chain.

• End products include lactic acid, ethanol, and other compounds.

• Regenerates NAD+ for glycolysis.

Krebs Cycle (Citric Acid Cycle)

The Krebs cycle completes the oxidation of glucose derivatives, generating NADH, FADH2, and ATP.

• Occurs in the cytoplasm (prokaryotes) or mitochondria (eukaryotes).

• Produces CO2 as a waste product.

Chapter 6: Microbial Growth

Classification of Microbes by Temperature Preference

Microbes are classified based on their optimal temperature ranges:

Group	Temperature Range (°C)	Example
Psychrophiles	−5 to 15	Deep ocean bacteria
Mesophiles	20 to 45	Most human pathogens
Thermophiles	55 to 80	Hot spring bacteria
Additional info: Hyperthermophiles	Above 80	Archaea in hydrothermal vents

pH Control in Culture Media

The pH of culture media is controlled to maintain optimal growth conditions for microbes. Buffers are often added to prevent drastic pH changes caused by microbial metabolism.

Biofilms: Formation and Infection Potential

Biofilms are communities of microorganisms attached to surfaces and embedded in a self-produced matrix.

• Form on medical devices, teeth, and water pipes.

• Increase resistance to antibiotics and immune responses.

• Can cause persistent infections.

Chemically Defined vs. Complex Media

• Chemically defined media: Exact chemical composition is known.

• Complex media: Contains extracts (e.g., peptones, yeast extract); composition varies.

Colony Definition

A colony is a visible mass of microbial cells arising from a single cell or group of cells on solid media.

Binary Fission

Binary fission is the primary method of reproduction in prokaryotes, where one cell divides into two identical daughter cells.

Phases of Microbial Growth and Generation Time

Microbial growth in batch culture follows distinct phases:

Phase	Description
Lag	Cells adapt to new environment; little division
Log (Exponential)	Rapid cell division; population doubles at constant rate
Stationary	Growth rate slows; nutrients deplete, waste accumulates
Death	Cells die faster than they divide

Generation time is the time required for a cell to divide (or for a population to double).

Chapter 7: The Control of Microbial Growth

Definitions of Key Terms

• Sterilization: Destruction or removal of all forms of microbial life, including endospores.

• Disinfection: Destruction of vegetative pathogens on inanimate objects.

• Antisepsis: Destruction of vegetative pathogens on living tissue.

• Degerming: Mechanical removal of microbes from a limited area.

• Sanitization: Lowering microbial counts to safe public health levels.

• Biocide/Germicide: Agents that kill microbes.

• Bacteriostasis: Inhibition of bacterial growth without killing.

• Asepsis: Absence of significant contamination.

Effects of Microbial Control Agents on Cellular Structures

• Damage to cell membranes (loss of selective permeability).

• Denaturation of proteins and enzymes.

• Damage to nucleic acids (DNA/RNA).

Comparison of Physical Methods: Autoclaving, Boiling, Pasteurization, Dry Heat

Method	Conditions	Effectiveness
Autoclaving	121°C, 15 psi, 15 min	Sterilizes; kills endospores
Boiling	100°C, 10 min	Kills most pathogens; not endospores
Pasteurization	63°C for 30 min or 72°C for 15 sec	Reduces pathogens; does not sterilize
Dry Heat	170°C, 2 hr	Sterilizes; slower than moist heat

Factors Contributing to Effective Disinfection

• Concentration of disinfectant

• Presence of organic matter

• pH

• Contact time

• Type of microbe present

Chemical Sterilizers

• Examples: Ethylene oxide, glutaraldehyde, peracetic acid

• Used for heat-sensitive materials

Microbial Type and Control Effectiveness

The susceptibility of microbes to control methods varies:

• Endospores are highly resistant.

• Gram-negative bacteria are generally more resistant than Gram-positive.

• Mycobacteria, protozoan cysts, and some viruses are also resistant to many agents.

Additional info: For exam preparation, review all definitions, processes, and comparisons. Practice applying concepts to clinical and laboratory scenarios.