Enzymes and Metabolism

Types of Enzymes

Extracellular Enzymes

• Produced by: Rough ER-associated ribosomes
• Transport: Vesicles to Golgi, then exported out of the cell
• Examples: Pancreatic cells producing digestive enzymes, bacterial enzymes for external material breakdown

Intracellular Enzymes

• Produced by: Free-floating ribosomes in the cytoplasm
• Usage: Inside the cell
• Example: DNA polymerase (used in the nucleus during DNA replication)

Efficiency of Reactions

• Energy Transformation: Not 100% efficient. Heat energy is a byproduct and considered "lost" as it is not usable for other cellular processes
• Examples: Cell respiration is about 90% inefficient. Majority of energy lost as heat
• Usage of Heat: Warm-blooded animals use heat to control body temperature (e.g., shivering to generate ATP for heat)

Metabolic Pathways

Linear Pathways

• Example: Glycolysis

Cyclical Pathways

• Examples: Krebs cycle, Calvin cycle

Commonalities

• Chains of enzymes and intermediate products
• Sequential enzyme reactions converting substrate to final product

Enzyme Control and Inhibition

Non-competitive (Allosteric) Inhibition

• Mechanism: Substance binds to allosteric site, changing active site shape, making it non-functional
• Example: Isoleucine

Competitive Inhibition

• Mechanism: Molecule with similar shape competes for active site with the real substrate
• Example: Statins (inhibit enzyme producing cholesterol)

Feedback (End Product) Inhibition

• Mechanism: Final product of a chain inhibits the first enzyme by binding to allosteric site
• Example: Threonine to isoleucine pathway
• Type: Negative feedback loop, typically reversible

Permanent Inhibition

• Examples: Mercury, arsenic, penicillin (inhibits bacterial enzyme transpeptidase)
• Impact: Permanent inhibition causing systemic damage, beneficial in antibiotics targeting bacterial enzymes
• Human Application: Penicillium fungus-based penicillin inhibits bacterial cell wall synthesis without harming human cells