Glucose Metabolism and Energy Production

Energy Sources and Electron Carriers

• Triphosphate is a compound that is oxidized to release energy and is also called an electron donor.
• Electron carriers carry electrons that are removed during the oxidation of energy sources.

Glucose Breakdown

• Glucose is a key energy-storing molecule that is metabolized by almost all cells for energy.
• Glucose metabolism is relatively simple, and other organic molecules are converted to glucose for energy harvesting.
• Glycolysis is the breakdown of glucose to pyruvate, yielding two molecules of ATP per molecule of glucose.
• If oxygen is absent, fermentation occurs, and pyruvate is converted into lactate or ethanol and CO2.
• If oxygen is present, cellular respiration occurs.

Alternative Pathways to Glycolysis

• Pentose Phosphate Pathway (Hexose Monophosphate Shunt) occurs simultaneously with glycolysis and breaks down pentose sugars and glucose.
• Intermediate pentoses are used for nucleic acid synthesis and amino acid synthesis.
• This pathway is an important producer of reduced coenzyme NADPH used for biosynthetic reactions.
• Entner-Doudoroff Pathway uses 6-phosphogluconate dehydratase and 2-keto-3-deoxyphosphogluconate aldolase to create pyruvate from glucose.
• This pathway produces 1 molecule of NADH, 1 molecule of NADPH, and 1 molecule of ATP.

Glucose Breakdown Overview

• Cellular respiration breaks down pyruvate into carbon dioxide and water.
• This process requires oxygen and generates ATP from reduced substrates.

Electron Transport Chain

• The electron transport chain is the last phase of respiration, generating ATP from reduced substrates.
• It consists of a sequence of carrier molecules through which electrons pass.
• The electron transport chain occurs in the plasma membrane and is different in different bacteria.

Factors Affecting Bacterial Growth

• Water: 80% of bacterial cells consist of water, and dehydration is detrimental to most bacteria.
• Oxygen: Most life forms depend on oxygen for survival and growth.
• Carbon dioxide: Autotrophic organisms use CO2 as a source of carbon, while heterotrophic bacteria require some CO2 from exogenous sources.
• Temperature: Psychrophiles grow below 20°C, mesophiles grow between 20-40°C, and thermophiles grow at higher temperatures.
• Hydrogen Ion Concentration: Most bacteria have an average pH requirement of 7.2-7.6.
• Light: Most bacteria prefer darkness for growth, while some require sunlight.
• Osmotic Pressure: Bacteria have a wide range of osmotic tolerance, and 0.5% NaCl is added to culture media to provide suitable osmolarity.

Microbial Growth Requirements

• Physical growth factors include gaseous and humidity requirements.
• Based on O2 requirements, microbes can be divided into microaerophilic, aerophilic, and anaerobic categories.

Bacterial Growth Curve

• The bacterial growth curve represents the number of live cells in a population over time.
• There are four distinct phases: lag phase, exponential (log) phase, stationary phase, and death phase.

Bacterial Growth Curve Phases

Lag Phase

• Characterized by cell activity but no growth.
• Bacteria adjust to the new environment, synthesizing proteins, enzymes, RNA, and other molecules necessary for multiplication.

Log (Exponential) Phase

• Time of rapid cell doubling, with cells dividing regularly by binary fission.
• Metabolic activity is high, generating DNA, RNA, cell wall components, and other substances necessary for growth.
• Antibiotics and disinfectants are most effective during this phase.

Energy Sources

• Triphosphate is an energy source compound that is oxidized to release energy, also known as an electron donor.
• Electron carriers carry electrons that are removed during oxidation of the energy source.

Glucose Breakdown

• Glucose is a key energy-storing molecule that is metabolized by nearly all cells for energy.
• Glucose metabolism is fairly simple, and other organic molecules are converted to glucose for energy harvesting.
• Glycolysis breaks down glucose to pyruvate, yielding two molecules of ATP per molecule of glucose, and occurs in the cytosol without requiring O2.
• If oxygen is absent, fermentation occurs, and pyruvate is converted into either lactate or ethanol and CO2.
• If O2 is present, cellular respiration occurs.

Alternative Pathways to Glycolysis

• Some bacteria have alternative pathways for glucose degradation, such as the Pentose Phosphate Pathway and the Entner-Doudoroff Pathway.
• The Pentose Phosphate Pathway occurs simultaneously with glycolysis, providing breakdown of both pentose sugar and glucose.
• The Entner-Doudoroff Pathway uses 6-phosphogluconate dehydratase and 2-keto-3-deoxyphosphogluconate aldolase to create pyruvate from glucose, producing 1 molecule NADH, 1 molecule NADPH, and 1 molecule of ATP.

Glucose Breakdown Overview

• Cellular respiration breaks down pyruvate into carbon dioxide and water, requiring oxygen.
• Fermentation occurs in the absence of oxygen.

Electron Transport Chain

• The electron transport chain is the last phase of respiration, generating ATP from reduced substrates.
• It consists of a sequence of carrier molecules through which electrons pass.
• The electron transport chain occurs in the plasma membrane and is different in different bacteria.

Factors Affecting Bacterial Growth

• Water is essential for bacterial growth, making up 80% of the bacterial cell.
• Oxygen is required for most bacteria as a terminal electron acceptor in their respiratory chain.
• Carbon dioxide is provided by cellular metabolism and the environment, and is required for autotrophic and heterotrophic bacteria.
• Temperature, hydrogen ion concentration, light, osmotic pressure, and symbiosis and antagonism also affect bacterial growth.

Aseptic Techniques and Health and Safety

• Ensuring a contamination-free environment is crucial in a microbiology laboratory.
• Sterilized equipment should be easily accessible, and working beside a Bunsen burner creates an upward flow of air through convection.
• Test tubes containing sensitive biological samples should be flamed around the cap and neck, and agar plates should be opened facing away from the user.

Microbiology/Immunology Lab

• Streak plating is a technique used in microbiology laboratories.

Independent Study

• Bacteria can be classified into two broad categories: gram positive and gram negative.
• Each category has different growth requirements and type of culture media.

Bacterial Growth Factors

• Water, oxygen, carbon dioxide, temperature, hydrogen ion concentration, light, osmotic pressure, and symbiosis and antagonism are factors that affect bacterial growth.