2025_02_19_09am_Maulik_Catabolic Energy and Anabolic Selective Toxicity (L1)_22279621 notes

What are the key pathways used by bacteria to obtain energy from glucose and their differences?

1. Embden-Meyerhof-Parnas (Glycolytic Pathway):

   • Used by most bacteria.

   • Net result: 2 ATP and 2 pyruvate.

   • Similar to the glycolysis pathway in eukaryotes.

2. Entner-Doudoroff Pathway:

   • Common in aerobic bacteria (e.g., Azotobacter and Pseudomonas).

   • Lacks phosphofructokinase (PFK), bypassing the PFK step.

   • Net result: 1 ATP and 1 pyruvate.

3. Pentose Phosphate Cycle (HMP Shunt):

   • Provides nucleic acid precursors and NADPH+H+.

   • Used by cyanobacteria and other organisms.

   • Converts glucose into pentose sugars.

How do prokaryotes catabolize macromolecules and what are the primary catabolic pathways?

1. Macromolecule Hydrolysis:

   • Extracellular enzymes break down large macromolecules in the environment into smaller low-molecular-weight products.

2. Transport into the Cell:

   • These low-molecular-weight metabolites are transported across the cytoplasmic membrane into the protoplast (the cell's interior).

   • Active transport systems concentrate these metabolites.

3. Catabolic Pathways:

   • Once inside, the metabolites are processed via 3 catabolic pathways, all converging on the primary end product: pyruvate.

What happens to pyruvate under aerobic conditions in prokaryotes?

1. Complete Oxidation of Pyruvate:

   • Pyruvate is completely oxidized to CO2 and H2O.

   • This process involves the formation of acetyl-CoA and proceeds through the tricarboxylic acid cycle (TCA cycle) and oxidative phosphorylation.

2. Energy Generation:

   • Substrate-level phosphorylation and oxidative phosphorylation in the electron transport chain (ETC) result in the production of ATP.

3. Anabolic Precursors:

   • The process also generates anabolic precursors used for building cellular components.

How is ATP generated through substrate-level phosphorylation?

• Substrate-level phosphorylation is a process where phosphate is transferred from a high-energy organic phosphoryl intermediate to ADP, forming ATP.

• This process occurs independently of the electron transport chain and does not require oxygen.

What is the ultimate electron acceptor in anaerobic respiration in prokaryotes, and where does this process occur?

• In anaerobic respiration, the ultimate electron acceptor from the terminal electron transport chain can be NO₃²⁻ (nitrate), SO₄²⁻ (sulfate), or CO₂ (carbon dioxide).

• Anaerobic respiration occurs in the cell membrane, as prokaryotes lack mitochondria.

In E. coli, a facultative gram-negative bacterium, what is notable about the outer membrane, and what respiratory chain does it use?

• The outer membrane of E. coli is predominantly composed of lipopolysaccharide (LPS) rather than phospholipids.

• E. coli uses the aerobic respiratory chain for energy production when oxygen is available. This involves the transfer of electrons through various membrane-associated complexes, culminating in the reduction of oxygen to water in the electron transport chain.

Where is the electron transport chain located in eukaryotes and prokaryotes, and what is its function?

• In eukaryotes, the electron transport chain is located in the inner mitochondrial membrane.

• In prokaryotes, the electron transport chain is located in the plasma membrane.

• Electrons move through the electron transport chain from a higher to lower energy state, driving the synthesis of ATP via oxidative phosphorylation.

What happens to pyruvate under anaerobic conditions, and what are the functions of fermentative pathways?

• Under anaerobic conditions, pyruvate is catabolized by fermentation in the absence of a complete TCA cycle and aerobic electron transport.

• Fermentation is less efficient in ATP production, causing anaerobes and facultative anaerobes to grow slower as they produce fewer moles of ATP per mole of substrate oxidized.

Fermentative Pathways Function To:

1. Produce ATP through substrate-level phosphorylation (and anaerobic respiration in some anaerobes).

2. Regenerate oxidized cofactors like NAD+, NADP+, and FAD+.

3. Provide additional anabolic precursors for anabolism.

How do bacteria make ATP during fermentation and respiration?

• Fermentation: Bacteria make ATP by substrate-level phosphorylation.

• Respiration: Bacteria make ATP through a combination of substrate-level phosphorylation and oxidative phosphorylation.

How is fermentation of pyruvate used to distinguish different bacteria in clinical laboratories?

• Fermentation of pyruvate by different microorganisms results in different end products.

• Clinical laboratories use these fermentation pathways and their specific end products to distinguish between different bacterial species.

Why is fermentation considered inefficient, and how is the profile of fermentation products useful in clinical diagnostics?

• Fermentation is inefficient because it produces large amounts of organic acids and alcohols.

• The compounds produced during fermentation depend on the specific pathway used by the species.

• The profile of fermentation products serves as a diagnostic aid in the clinical laboratory to differentiate bacterial species.

What is industrial-scale fermentation, and how is it applied in biotechnology, such as in the production of recombinant insulin?

• Industrial-scale fermentation is the large-scale cultivation of microorganisms to produce bioproducts through fermentation processes.

• It is used in biotechnology for applications like the production of recombinant insulin.

• In this process, microorganisms (often bacteria or yeast) are genetically engineered to produce recombinant proteins (like insulin) by inserting the human insulin gene into their genome.

• The microorganisms ferment and produce the desired protein, which is then purified and used as a treatment in medicine.

How do prokaryotes biosynthesize components of biomass?

• Prokaryotes use similar anabolic pathways as eukaryotes to biosynthesize components of biomass.

What are some examples of unique macromolecules in prokaryotes?

Examples include peptidoglycan, lipopolysaccharide, and teichoic acids.

How do antibiotics work to target bacteria?

Antibiotics like penicillin inhibit bacterial cell wall synthesis by targeting peptidoglycan transpeptidase, a key enzyme in bacterial cell wall formation.

What is selective toxicity in terms of antibiotics?

• Selective toxicity refers to the ability of antibiotics to target mechanisms unique to prokaryotes, such as cell wall biosynthesis and 70S ribosomes, without affecting eukaryotic cells, which have 80S ribosomes.

What are polysomes in bacteria?

• Polysomes are formed when multiple ribosomes translate the same mRNA molecule simultaneously, increasing protein synthesis efficiency in bacteria.

What are the five main antibacterial drug targets in bacteria?

The five main antibacterial drug targets in bacteria are cell-wall synthesis, DNA gyrase, metabolic enzymes, DNA-directed RNA polymerase, and protein synthesis.

How do drugs targeting cell-wall synthesis work?

Drugs targeting cell-wall synthesis inhibit the formation of the bacterial cell wall, which is crucial for bacterial integrity and survival (e.g., penicillin targeting peptidoglycan synthesis).

What role does DNA gyrase play in bacterial cells, and how do antibiotics target it?

DNA gyrase is involved in DNA supercoiling. Antibiotics such as fluoroquinolones inhibit DNA gyrase, preventing DNA replication.

What are some examples of drugs targeting metabolic enzymes in bacteria?

Drugs targeting metabolic enzymes inhibit key biochemical pathways. For example, sulfonamides inhibit folic acid synthesis in bacteria.

How do antibiotics that target DNA-directed RNA polymerase function?

Antibiotics like rifampicin bind to DNA-directed RNA polymerase, preventing transcription and thereby halting bacterial protein synthesis.

What is the mechanism of antibiotics targeting protein synthesis?

• Antibiotics such as tetracyclines and macrolides target bacterial ribosomes, inhibiting protein synthesis and bacterial growth.

What is the main mechanism of action of the biocide triclosan?

Triclosan inhibits type 2 (bacterial) fatty acid synthesis, which is an essential lipid anabolic pathway in bacteria.

Which enzyme does triclosan interact with to exert its effect?

• Triclosan interacts directly with enoyl acyl carrier protein reductase (FabI), an enzyme involved in bacterial fatty acid biosynthesis.

How does triclosan inhibit enzyme catalysis?

• Triclosan forms a stable ternary complex between FabI, NAD+, and triclosan, thereby inhibiting enzyme catalysis.

Why is inhibition of fatty acid synthesis important in bacterial cells?

• Fatty acid synthesis is crucial for forming bacterial membranes. Inhibition of this pathway disrupts membrane integrity and bacterial growth.

What is the mechanism of action for chloramphenicol, macrolides, and lincosamides in bacterial cells?

• Chloramphenicol, macrolides, and lincosamides bind to the 50S ribosomal subunit in bacteria, preventing the formation of peptide bonds and inhibiting protein synthesis.

How do aminoglycosides disrupt bacterial protein synthesis?

Aminoglycosides bind to the 30S ribosomal subunit, impairing the proofreading ability of the ribosome, leading to the production of faulty proteins.

What is the primary action of tetracycline in bacterial protein synthesis?

Tetracycline binds to the 30S ribosomal subunit, blocking the attachment of tRNAs and inhibiting protein synthesis.

Why do these antibiotics selectively target bacterial cells without harming eukaryotic cells?

These antibiotics selectively target bacterial ribosomes (which differ structurally from eukaryotic ribosomes), thus inhibiting bacterial protein synthesis while having minimal effects on eukaryotic cells.