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Overview of Enzyme Characteristics and Cellular Respiration

Overview of Enzyme Characteristics

  • Enzymes are primarily composed of proteins.

  • Some enzymes require nonprotein cofactors for their activity.

  • Enzymes act as organic catalysts, speeding up the rate of cellular reactions.

  • Enzymes lower the activation energy needed for a chemical reaction to proceed.

Unique Features of Enzymes

  • Enzymes have specific characteristics, including shape, specificity, and function.

  • They provide an active site that binds to target molecules called substrates.

  • Enzymes are significantly larger than their substrates.

  • They associate closely with substrates but do not become part of the reaction products.

  • Enzymes are not consumed or permanently changed by the reactions they catalyze.

  • They can be recycled and used in extremely low concentrations.

  • Enzymes are highly sensitive to changes in temperature and pH.

  • Regulation of enzyme activity can occur through feedback mechanisms and genetic processes.

Enzyme Summary

  • Enzyme Characteristics:

    • Composed mostly of protein.

    • Lower "Energy of Activation" of chemical reactions.

    • Unchanged throughout the reaction.

  • Enzyme Locations:

    • Endoenzymes and Exoenzymes.

  • Factors Affecting Enzyme Activity:

    • Substrate Concentration: Higher substrate levels can enhance activity.

    • Sensitivity to Environmental Conditions: Temperature and pH can affect function.

    • Regulation Mechanisms:

    • 1. Direct (enzyme level):

      • Competitive Inhibition: A molecule competes for the substrate site.

      • Non-competitive Inhibition:

      • Allosteric Regulation: A molecule binds to a site other than the active site, which can activate or inhibit the enzyme.

      • Feedback Inhibition: Common in metabolic pathways

    • 2. Genetic Level:

      • Induced or repressed transcription regulates enzyme levels.

Cellular Respiration: Harvesting Chemical Energy

  • Chapter Focus:

    • The role of redox reactions in cellular respiration.

    • The three phases of cellular respiration, including input and output molecules of each stage and their locations in eukaryotic cells.

    • Flow of carbon atoms through cellular respiration phases.

    • Examples of energy coupling in all phases of respiration.

    • Energy use in synthesizing ATP through the electron transport chain.

Learning Objectives for Chapter 7

  • Role of redox reactions in cellular respiration.

  • Three phases of cellular respiration:

    • Inputs/outputs of each stage; location in eukaryotic cells.

    • Carbon atom flow in the first two phases.

    • Examples of energy coupling throughout.

    • Energy from electron transport for ATP synthesis.

  • Number of ATP produced in respiration based on energy carrier output.

  • Definition and purpose of fermentation in the absence of O2.

  • Metabolism of proteins and fats; entry points into cellular respiration.

  • Regulation of cellular respiration via allosteric activation and feedback inhibition.

Importance of Cellular Respiration

  • Critical for growth and survival of animals, plants, fungi, and most protists.

  • Mitochondrial disorders impact energy metabolism and are linked to various age-related issues, including Alzheimer’s disease.

Metabolism

  • Definition: All biochemical and physical processes within a cell.

  • Types of Chemical Reactions:

    • Catabolism: Energy-releasing reactions that break down molecules.

    • Anabolism: Energy-consuming reactions that build complex molecules.

Nutritional Types

  • Determinants of Nutritional Type:

    • Carbon Source:

    • Heterotrophs: Obtain organic compounds from other living organisms.

    • Autotrophs: Use inorganic carbon sources (CO2).

    • Energy Source:

    • Chemotrophs: Obtain energy from chemical compounds.

    • Phototrophs: Obtain energy from light via photosynthesis.

Classifications of Organisms

  • By Carbon Source:

    • Chemoautotrophs: Inorganic chemicals.

    • Chemoheterotrophs: Organic compounds (e.g., animals, fungi).

    • Photoautotrophs: Inorganic chemicals, utilizing light (e.g., plants, algae).

    • Photoheterotrophs: Organic compounds, utilizing light

Division of Cellular Respiration

  • Mitochondrial Function:

    • ATP forms in mitochondria as part of cellular respiration reactions.

Aerobic vs Anaerobic Respiration

  • Aerobic Respiration:

    • Requires oxygen.

    • Involves electron transport to oxygen as the final electron acceptor.

  • Anaerobic Respiration:

    • Involves alternative electron acceptors (NO3, SO4, etc.).

    • Fermentation is a pathway used when oxygen is scarce.

Overview of Catabolic Pathways

  • Aerobic Respiration Overview:

    • Glycolysis breaks glucose ($C6H{12}O_6$) into two pyruvate molecules, producing ATP and NADH.

  • Anaerobic Respiration Overview:

    • Similar glycolytic process, but with a different terminal electron acceptor.

  • Maximum ATP Production:

    • Aerobic Respiration Theoretical Maximum: 38 ATP. - Varies with microbe efficiency.

Relationship between Cellular Respiration and Photosynthesis

  • Cellular respiration and photosynthesis are integral to the carbon cycle.

  • Photosynthesis generates food and oxygen for cellular respiration, while respiration consumes them.

Redox Reactions

  • Oxidation: Removal of electrons; the electron donor is oxidized.

  • Reduction: Addition of electrons; the electron acceptor is reduced.

  • Mnemonic: OIL RIG (Oxidation Is Loss; Reduction Is Gain).

Electron Transport System (ETS)

  • Comprised of multiple protein complexes transferring electrons to ultimately produce ATP via oxidative phosphorylation.

  • H+ gradient created by pumping protons across the membrane, driving ATP synthesis.

ATP Production Mechanisms

  • Substrate-level Phosphorylation: Direct transfer of a phosphate group to ADP.

  • Oxidative Phosphorylation: Involves the electron transport chain and chemiosmosis.

  • Photophosphorylation: Formation of ATP utilizing sunlight energy.

Summary of ATP Production

  • Maximum Yield from Glucose is 38 ATP.

  • 32 ATP are typically produced by cellular respiration under optimal conditions; this is about 33-38% efficiency of glucose oxidation.

  • Energy from ATP hydrolysis: approximately $7.0 ext{ kcal/mol}$.

Fermentation and Anaerobic Respiration

  • Fermentation allows ATP production in the absence of oxygen.

  • Distinction lies in electron acceptors:

    • Fermentation uses organic molecules; oxygen isn’t the final electron acceptor.

    • Anaerobic respiration utilizes an electron transport chain with non-oxygen molecules.

Types of Fermentation

  • Lactic Acid Fermentation: Converts pyruvate into lactic acid. Occurs in certain bacteria and human muscle.

  • Alcoholic Fermentation: Converts pyruvate into ethanol and CO2, utilized by yeast and in alcoholic beverage production.

Metabolism of Other Molecules

  • Fats: Yield higher energy than carbohydrates and proteins.

  • Proteins: Enter oxidative pathways after deamination and are utilized as fuel.

Regulation of Metabolic Pathways

  • Metabolic pathways can be regulated by feedback inhibition to balance the production of ATP and preserve glucose.

  • Regulation can involve competitive inhibition or enzyme activity modulation based on substrate levels.

Integration of Cellular Metabolism

  • Cellular metabolic pathways exhibit interrelationships, allowing metabolites to be funneled into various biosynthetic pathways or redirected for energy production.