Microbial Metabolism and Enzyme Function: Study Notes

Microbial Metabolism and Enzyme Function

Metabolism, Catabolism, and Anabolism

Metabolism refers to all chemical reactions occurring within a cell or organism, encompassing both energy-releasing and energy-consuming processes.

• Catabolism: The breakdown of complex molecules into simpler ones, releasing energy. Example: Glycolysis.

• Anabolism: The synthesis of complex molecules from simpler ones, requiring energy input. Example: Protein synthesis.

Example: During cellular respiration, glucose is catabolized to produce ATP, while amino acids are anabolized to form proteins.

ATP Formation in Prokaryotes and Eukaryotes

ATP (adenosine triphosphate) is the universal energy currency required by both prokaryotic and eukaryotic cells to drive cellular processes such as biosynthesis, transport, and motility.

• Both cell types use glycolysis, the Krebs cycle, and oxidative phosphorylation to generate ATP.

• ATP is essential for maintaining cellular structure and function.

Proteome and Genome

The proteome is the entire set of proteins expressed by a genome, cell, tissue, or organism at a certain time. The genome contains all the genetic information required to produce the proteome.

• The proteome reflects the functional output of the genome under specific conditions.

Factors Affecting Enzyme Activity

Enzyme activity is influenced by several factors:

• Temperature: Each enzyme has an optimal temperature for activity.

• pH: Enzymes function best at specific pH ranges.

• Substrate concentration: Increased substrate can increase activity up to a saturation point.

Enzyme Inhibitors: Competitive and Noncompetitive

Enzyme inhibitors reduce or prevent enzyme activity.

• Competitive inhibitors: Bind to the active site, blocking substrate access.

• Noncompetitive inhibitors: Bind to a different site, altering enzyme shape and function.

Example: Sulfanilamide is a competitive inhibitor of the enzyme involved in folic acid synthesis in bacteria.

Mechanism of Action of Sulfanilamide Drugs

Sulfanilamide drugs inhibit bacterial growth by competitively inhibiting the enzyme dihydropteroate synthase, which is essential for folic acid synthesis. This prevents bacteria from synthesizing DNA, RNA, and proteins.

Enzyme Quantity vs. Quality

Enzyme quantity refers to the amount of enzyme present, while enzyme quality refers to the enzyme's functional efficiency or activity.

• High quantity does not always mean high activity if the enzyme is not functional.

Protein Denaturation

Protein denaturation is the loss of a protein's native structure, resulting in loss of function. Methods to denature proteins include:

• Heat

• Extreme pH

• Chemical agents (e.g., urea, detergents)

ATP Generation from ADP

ATP is generated from ADP (adenosine diphosphate) by the addition of a phosphate group, a process called phosphorylation. This occurs during cellular respiration and photosynthesis.

• Equation: $\text{ADP} + \text{P}_i + \text{energy} \rightarrow \text{ATP}$

Substrate-Level Phosphorylation vs. Oxidative Phosphorylation

Type	Description	Example
Substrate-level phosphorylation	Direct transfer of a phosphate group to ADP from a phosphorylated intermediate	Glycolysis
Oxidative phosphorylation	ATP synthesis using energy from electron transport chain and chemiosmosis	Electron transport chain in mitochondria

Classification of Microbes by Energy and Carbon Source

Type	Energy Source	Carbon Source
Photoautotroph	Light	CO2
Photoheterotroph	Light	Organic compounds
Chemoautotroph	Inorganic chemicals	CO2
Chemoheterotroph	Organic chemicals	Organic compounds

Outcomes of Glycolysis, Aerobic Respiration, Anaerobic Respiration, and Fermentation

• Glycolysis: Converts glucose to pyruvate, producing 2 ATP and 2 NADH.

• Aerobic respiration: Complete oxidation of glucose to CO2 and H2O, yielding up to 38 ATP.

• Anaerobic respiration: Uses alternative electron acceptors (not O2), less ATP than aerobic.

• Fermentation: Incomplete oxidation, regenerates NAD+, produces organic end products and 2 ATP.

Catabolism of Nutrient Classes

Cells catabolize carbohydrates, lipids, and proteins to produce energy. Carbohydrates are typically the primary energy source, but lipids and proteins can be used when necessary.

Aerobic vs. Anaerobic Respiration vs. Fermentation

Process	Oxygen Required?	Final Electron Acceptor	ATP Yield
Aerobic Respiration	Yes	O2	~38
Anaerobic Respiration	No	Inorganic molecules (e.g., NO3-)	Varies, less than aerobic
Fermentation	No	Organic molecules	2

ATP Production During Glycolysis, Krebs Cycle, and Electron Transport Chain

• Glycolysis: 2 ATP (net) via substrate-level phosphorylation

• Krebs cycle: 2 ATP (per glucose) via substrate-level phosphorylation

• Electron transport chain (ETC): Up to 34 ATP via oxidative phosphorylation

Electron Transport Chain Location

• Prokaryotes: Plasma membrane

• Eukaryotes: Inner mitochondrial membrane

Final Electron Receptor Molecules in Anaerobic Organisms

Organism	Final Electron Acceptor
Bacillus	Nitrate (NO3-)
Pseudomonads	Sulfate (SO42-)
Desulfovibrio	Sulfate (SO42-)
Enterics	Nitrate (NO3-)

Characteristics of Fermentation

• Occurs in absence of oxygen

• Regenerates NAD+ for glycolysis

• Produces organic end products (e.g., lactic acid, ethanol)

• Yields 2 ATP per glucose

How Fermentation Generates Energy

Fermentation allows glycolysis to continue by regenerating NAD+ from NADH, enabling the cell to produce ATP in the absence of oxygen.

Chemical End Products of Fermentation

• Lactic acid

• Ethanol

• CO2

• Acetic acid

Microbial Enzyme Release: Lipases, Proteases, Peptidases

Microbes produce and release these enzymes to break down complex macromolecules in their environment for nutrient acquisition.

• Lipases: Hydrolyze lipids into fatty acids and glycerol.

• Proteases: Hydrolyze proteins into peptides and amino acids.

• Peptidases: Further break down peptides into amino acids.