Microbiology: Cellular Respiration and Glycolysis

• Microbiology encompasses the study of microorganisms, including bacteria, archaea, fungi, protists, and viruses.
• These organisms are central to various biological processes, including cellular respiration, fermentation, and photosynthesis.

Cellular Respiration

• Cellular respiration is a metabolic process that converts biochemical energy from nutrients into adenosine triphosphate (ATP).
• ATP is the energy currency of the cell, providing power for various cellular activities.
• The process involves a series of metabolic pathways where glucose is oxidized to carbon dioxide and water.
• Aerobic respiration requires oxygen and yields a significantly higher amount of ATP compared to anaerobic processes.
• The general equation for aerobic respiration is: C6H12O6 + 6O2 → 6CO2 + 6H2O + energy (ATP).

Glycolysis

• Glycolysis is the initial stage of cellular respiration, occurring in the cytoplasm.
• It involves the breakdown of glucose into two molecules of pyruvate.
• Glycolysis produces a small amount of ATP and NADH (a reduced form of nicotinamide adenine dinucleotide).
• It does not require oxygen and can occur under both aerobic and anaerobic conditions.

Krebs Cycle (Citric Acid Cycle)

• The Krebs cycle takes place in the mitochondrial matrix in eukaryotes and the cytoplasm in prokaryotes.
• Pyruvate is converted into acetyl-CoA, which enters the cycle.
• The cycle oxidizes acetyl-CoA, releasing carbon dioxide and producing ATP, NADH, and FADH2 (flavin adenine dinucleotide).

Electron Transport Chain (ETC)

• The electron transport chain is located in the inner mitochondrial membrane in eukaryotes and the cytoplasmic membrane in prokaryotes.
• NADH and FADH2 donate electrons, which are passed through a series of protein complexes.
• This process generates a proton gradient across the membrane, which is used to synthesize ATP through oxidative phosphorylation.
• Oxygen acts as the final electron acceptor, forming water.

ATP Production

• ATP is produced through substrate-level phosphorylation and oxidative phosphorylation.
• Substrate-level phosphorylation involves the direct transfer of a phosphate group from a substrate molecule to ADP.
• Oxidative phosphorylation uses the energy from the electron transport chain to create a proton gradient, driving ATP synthase to produce ATP.
• Aerobic respiration can generate approximately 32 ATP molecules per glucose molecule.

Anaerobic vs. Aerobic Processes

• Aerobic processes require oxygen, while anaerobic processes do not.
• Aerobic respiration yields significantly more ATP compared to anaerobic respiration or fermentation.
• Anaerobic respiration uses electron acceptors other than oxygen, such as sulfate or nitrate.
• Fermentation is an anaerobic process that regenerates NAD+ from NADH, allowing glycolysis to continue.

Fermentation

• Fermentation is a metabolic process that extracts energy from carbohydrates in the absence of oxygen.
• It is used by various microorganisms and in muscle cells during intense exercise when oxygen supply is limited.
• Fermentation regenerates NAD+ by passing electrons from NADH to an organic molecule.
• Common fermentation products include lactic acid and ethanol.

Microbial Fermentation Types

• Lactic acid fermentation involves the conversion of pyruvate to lactic acid.
• Ethanol fermentation converts pyruvate to ethanol and carbon dioxide.
• Various other fermentation types produce different organic acids, alcohols, and gases.
• Fermentation is used in the production of foods such as yogurt, cheese, beer, and wine.

Photosynthesis

• Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy.
• It uses carbon dioxide and water to produce glucose and oxygen.
• The general equation for photosynthesis is: 6CO2 + 6H2O + light energy → C6H12O6 + 6O2.
• Photosynthesis occurs in chloroplasts in eukaryotes and in the cytoplasm of photosynthetic bacteria.

Light-Dependent Reactions

• Light-dependent reactions occur in the thylakoid membranes of chloroplasts and involve the capture of light energy by chlorophyll.
• This energy is used to split water molecules, releasing oxygen, protons, and electrons.
• ATP and NADPH are produced during these reactions.

Light-Independent Reactions (Calvin Cycle)

• Light-independent reactions (Calvin cycle) occur in the stroma of chloroplasts.
• Carbon dioxide is fixed and converted into glucose using ATP and NADPH generated during the light-dependent reactions.

Photosynthetic Organisms

• Plants, algae, and cyanobacteria are the primary photosynthetic organisms.
• These organisms play a crucial role in the Earth's ecosystem by producing oxygen and converting carbon dioxide into organic compounds.
• Photosynthetic bacteria, such as cyanobacteria, were among the first organisms to perform oxygenic photosynthesis.

Metabolic Pathways

• Metabolic pathways are a series of interconnected biochemical reactions that convert specific molecules into other molecules.
• These pathways can be catabolic (breaking down molecules) or anabolic (building molecules).
• Cellular respiration, fermentation, and photosynthesis involve multiple interconnected metabolic pathways.

Catabolic Pathways

• Catabolic pathways break down complex molecules into simpler ones, releasing energy (e.g., cellular respiration).
• These pathways often involve the oxidation of molecules, releasing electrons that are captured by electron carriers such as NADH and FADH2.

Anabolic Pathways

• Anabolic pathways use energy to build complex molecules from simpler ones (e.g., photosynthesis).
• These pathways often involve the reduction of molecules, requiring electrons from electron carriers such as NADPH.