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Isoleucine and Feedback Inhibition

• Isoleucine: An amino acid that can inhibit the pathway of its own synthesis.

  • Used by cells to regulate metabolic pathways.

  • Important for maintaining homeostasis.

• Active Site Available: Indicates enzyme activity is ready to process initial substrates.

• Initial Substrate: Threonine is the starting molecule for the pathway.

  • Enzyme 1: Threonine deaminase.

• Feedback Inhibition:

  • Definition: The end product of a metabolic pathway inhibits an upstream process to maintain balance within the pathway.

  • Mechanism: Isoleucine binds to the allosteric site of an enzyme, halting the pathway.

  • Intermediate A through D: Products at different stages before reaching isoleucine as the end product.

  • Implications for Cells: Helps to prevent overproduction of isoleucine, thus conserving resources.

Localization of Enzymes Within the Cell

• Cellular Structure: Different locations within cells where enzymes are found.

  • Mitochondrion: A critical organelle for energy production.

  • Matrix contains enzymes essential for the second stage of cellular respiration.

  • Inner membrane houses enzymes for the third stage of cellular respiration.

Photosynthesis and Cellular Respiration

• Chemical Energy in Food: Fundamental concept linking photosynthesis and cellular respiration.

Big Ideas to Understand

• Photosynthesis:

  • Light-dependent reactions: Utilize sunlight to generate energy.

  • Calvin Cycle: Uses products of light-dependent reactions to synthesize sugars.

• Cellular Respiration:

  • Glycolysis: Initial glucose breakdown.

  • Citric Acid Cycle: Further degradation of glucose.

  • Oxidative Phosphorylation: Final energy extraction processes, including electron transport.

Autotrophic and Heterotrophic Nutrition

• Autotrophs: Organisms that produce their own food

  • Examples: Plants, cyanobacteria, multicellular alga, unicellular protists, purple sulfur bacteria.

• Heterotrophs: Organisms that depend on others for food; referred to as "other feeders."

• Significance: The source of carbon for all biological life comes predominantly from carbon dioxide, underscoring the interconnectedness of life forms through food chains.

ATP Production and Utilization

• ATP Formation: Occurs via photosynthesis and cellular respiration.

• Key Concept: Both processes involved in creating ATP, which powers most cellular activity.

Photosynthesis Detailed

• Definition: An anabolic process converting solar energy into stored chemical energy within carbohydrates.

• Overall Equation:

  • $6 CO<em>2 + 12 H</em>2O + ext{Light energy} → C<em>6H</em>{12}O<em>6 + 6 O</em>2 + 6 H_2O$

Two Stages of Photosynthesis

• Light Reactions:

  • Process: Splitting of water ($H_2O$) provides electrons and protons ($H^+$).

  • Outputs: Oxygen ($O_2$) is released as a by-product.

  • Electron Transport: Reduces NADP+ to NADPH and generates ATP from ADP.

• Calvin Cycle:

  • Utilizes ATP and NADPH produced in light reactions to synthesize sugars from carbon dioxide ($CO_2$).

  • Carbon fixation: critical starting phase for sugar synthesis.

The Calvin Cycle Overview

• Phases:

  1. Carbon fixation

  2. Reduction

  3. Regeneration of CO2 acceptor

• Key Biochemical Steps:

  • Three ATPs and NADPH utilized for sugar production.

  • Outputs include G3P which can be converted into glucose.

  • $3 ext{CO}_2$ enter and produce $1 ext{G3P}$.

Cellular Respiration Overview

• Definition: A catabolic process that releases energy via the breakdown of complex molecules.

• Overall Equation:

  • $C<em>6H</em>{12}O<em>6 + 6 O</em>2 → 6 CO<em>2 + 6 H</em>2O + ext{Energy (ATP + heat)}$

Stages of Cellular Respiration

1. Glycolysis: Splitting glucose into two pyruvate molecules.

   • Occurs aerobically and anaerobically.

2. Formation of Acetyl CoA: Link between glycolysis and citric acid cycle.

3. Citric Acid Cycle: Completes glucose breakdown, generating NADH and FADH2.

4. Oxidative Phosphorylation: Two processes:

   • Electron transport chain: Creating a proton gradient.

   • Chemiosmosis: ATP synthase uses the gradient to produce ATP.

Energy Efficiency of Cellular Respiration

• Maximum ATP Yield:

  • About 30 to 32 ATP can be generated per glucose molecule.

  • Plants also utilize cellular respiration to convert glucose into ATP.

Anaerobic Processes: Glycolysis and Fermentation

• Ability to function without oxygen:

  • Glycolysis can occur without oxygen,

  • Fermentation Types:

  • Alcohol Fermentation

  • Lactic Acid Fermentation

Energy Flow and Chemical Cycling

• Energy Flow:

  • Light energy sourced from the sun; subsequently converted into chemical energy.

  • Energy is lost as heat during these transformations.

• Chemical Cycling:

  • Chemicals cycle through ecosystems involving producers (plants) and decomposers (fungi and bacteria).

  • Chemicals are returned to the soil for use by plants again, completing the cycle.