Cell Metabolism and Activities

  • Lesson 2: Cellular Activities

    • Focus on how substances are processed for cell consumption and how substances are excreted.

    ATP (Adenosine Triphosphate)

    • Structure: Composed of:

      • Nitrogenous base: Adenine

      • Sugar: Ribose

      • Chain of three phosphate groups.

    • Function: The phosphate tail serves as the power source of ATP. Energy is stored in the bonds of the phosphates and released during hydrolysis (addition of water).

      • Energy release: Typically involves removal of the outer phosphate to convert ATP to ADP (Adenosine Diphosphate).

    Observational Exercise

    • Materials: Cut an apple, banana, or eggplant; observe mesocarp color change after exposure to air.

    • Note: This exercise is to correlate observations with biochemical reactions.

    Browning of Apples

    • Caused by enzymatic browning due to:

      • Exposure to oxygen when cut, leading to a reaction involving polyphenol oxidase (PPO) and polyphenols.

      • Formation of o-quinones, which react with amino acids to produce brown melanin.

      • Varieties of apples brown at different rates based on enzyme and polyphenol content.

    Unit 1: Enzymes

    • Definition: Globular proteins that act as catalysts to speed up chemical reactions without being consumed.

    • Characteristics:

    1. Speed up reactions drastically, reaching equilibrium quickly (up to 10 million times).

    2. Soluble in water; operate under specific pH and temperature conditions.

    3. Highly specific for substrates; one enzyme works with one substrate (complementary shape).

    4. Efficient; only small amounts required for substantial reactions.

    5. Usually require coenzymes (often vitamins) for activity.

    6. Named with suffix -ase related to substrates or reactions (e.g., urease).

Factors Affecting Enzyme Activity

  1. Temperature: Ideal at 30-45°C; reduced activity or denaturation beyond 60-70°C.

  2. Presence of Water: Essential for the reaction medium; absence suppresses activity.

  3. pH Levels: Each enzyme has an optimal pH range.

  4. Substrate Concentration: Increased concentration raises activity until saturation.

  5. Enzyme Concentration: More enzyme generally increases reaction rate with ample substrate.

  6. End Product Accumulation: High levels of products slow further enzymatic reactions.

  7. Inhibitors: Compounds that reduce enzyme activity (competitive vs. allosteric).

  8. Activators: Molecules that enhance enzyme activity (prosthetic groups/co-factors).

  9. Effects of Light/Radiation: Certain enzymes may be photo-sensitive.

Enzyme Action Theories

  • Two predominant theories:

    • Lock and Key Theory: Specific substrate fits into the enzyme's active site precisely.

    • Induced-Fit Hypothesis: Active site changes shape to accommodate the substrate.

Types of Enzyme Inhibition

  • Competitive Inhibition: Compete for active site.

  • Allosteric Inhibition: Bind elsewhere and change enzyme shape.

  • True/False review included regarding enzyme inhibition.

Unit 2: Oxidation-Reduction Reactions

  • Definition: Reactions changing oxidation states of atoms; gain/loss of electrons.

  • Oxidation involves loss of electrons or hydrogen, or gain of oxygen.

  • Reduction involves gaining electrons or hydrogen, or loss of oxygen.

Example Reaction

  • Hydrogen + Fluorine: H₂ + F₂ → 2 HF.

  • Half-reactions demonstrate oxidation and reduction processes.

Importance of Redox Reactions

  • Essential for biological processes (e.g., cellular respiration).

  • Used in industrial applications (e.g., metal extraction, electrochemical cells).

Unit 3: Metabolism

  • Definition: Total of chemical reactions sustaining cell life, consisting of metabolic pathways.

  • Anabolic Pathways: Build larger molecules (e.g., glucose from carbon dioxide) using ATP.

  • Catabolic Pathways: Breakdown of larger molecules releasing energy (e.g., glucose breakdown).

Cellular Respiration Overview

  • Enzymatic breakdown of food to produce ATP.

  • Primary equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP.

  • Stages of respiration:

    1. Glycolysis: Breakdown of glucose to pyruvate in cytoplasm.

    2. Link Reaction: Conversion of pyruvate to acetate in mitochondria.

    3. Krebs Cycle: Oxidation of acetate to carbon dioxide, producing ATP.

    4. Oxidative Phosphorylation: ATP formation via electron transport chain in mitochondria.

Glycolysis Phases

  1. Phosphorylation: Converts glucose to fructose-1,6-bisphosphate using ATP.

  2. Splitting: Produces two triose phosphate molecules.

  3. Oxidation: Removes hydrogen from triose phosphate; produces ATP and reduced NAD.

  4. Conversion to Pyruvate: Transformation of triose phosphate to pyruvate, generating ATP.

Anaerobic Processes

  • Fermentation: Occurs when oxygen is limited, producing alcohol or lactic acid.

Link Reaction & Krebs Cycle

  • Link Reaction: Pyruvate is converted to acetyl CoA, releasing carbon dioxide and NADH.

  • Krebs Cycle: Further oxidizes acetyl CoA, produces ATP, NADH, and FADH₂.

Electron Transport Chain & Chemiosmosis

  • Electron Transport: Electrons flow through complexes, pumping protons across membranes, generating a gradient.

  • ATP Synthesis: Uses proton flow to drive ATP synthesis via ATP synthase.

Photosynthesis Overview

  • Converts light energy to chemical energy; occurs in chloroplasts of green plants.

  • Chemical Equation: Involves carbon dioxide and water producing glucose and oxygen.

  • Two main processes in photosynthesis:

    1. Light Reactions: Convert solar energy to ATP and NADPH.

    2. Calvin Cycle: Uses ATP and NADPH to synthesize glucose from CO₂.

Factors Affecting Photosynthesis

  • Light intensity, carbon dioxide concentration, temperature, water availability, and pollutants.