Cellular Energy and Thermodynamics

Introduction to Cellular Energy

• Energy isn't matter but influences it.
• Work, scientifically, is moving an object across a distance.

Sources of Usable Energy

• The sun is the primary usable energy source.
• Plants use photosynthesis to turn solar energy into chemical energy.
• Animals get energy from eating plants or other animals.

Laws of Thermodynamics

• Energy cannot be created or destroyed, only transformed or transferred.
• Living things exchange energy and matter with their environment.
• Energy used by organisms transforms into unusable forms.
• Entropy, or disorder, always increases in the universe.
• Chemical reactions raise entropy by breaking bonds and rearranging molecules.
• A balance between order and chaos is essential for life.

Chemical Reactions and Energy

• Exergonic reactions release energy and are spontaneous.
• Endergonic reactions need energy and require work.
• Both reaction types need activation energy to start.
• Enzymes accelerate reactions by lowering activation energy.
• They bind to reactants and aid reactions without being altered.
• Enzymes are vital for many life functions and metabolic pathways.

ATP: The Energy Currency

• ATP (adenosine triphosphate) stores and transfers energy.
• ATP has three negatively charged phosphate groups that repel.
• Breaking bonds between phosphate groups releases energy.
• Hydrolysis, using water, splits ATP into ADP and a phosphate group.
• This process releases energy for cell activities.
• Cells use this energy for building molecules and moving substances.

Metabolic Pathways and Cellular Respiration

• Metabolic pathways are a chain of enzyme-catalyzed reactions.
• These pathways build or break down molecules for life.
• Understanding these pathways helps treat diseases like cancer and diabetes.
• Cellular respiration turns glucose into ATP.
• This process involves many steps and enzymes to efficiently produce energy.
• Cellular respiration will be explored further.

Conclusion: Importance of Energy

• Energy powers all cell activities and body functions.
• Understanding energy and metabolism is key to understanding life.
• Future lessons will explore metabolic processes and their importance.

Introduction to Photosynthesis

• Photosynthesis converts light energy into chemical energy using water and carbon dioxide, releasing oxygen.
• Plants, algae, and some bacteria perform photosynthesis.
• It provides the main energy source for life on Earth.
• Photosynthesis also produces oxygen, vital for aerobic organisms.
• Plants use the carbohydrates produced for growth and energy.
• Photosynthesis nourishes almost all life on Earth.

Process of Photosynthesis

• Light energy is converted into chemical energy through a series of reactions.
• Electrons move from donor to acceptor molecules during the process.
• Water is the initial electron donor, carbon dioxide is the final acceptor.
• Carbon dioxide combines with molecules to form carbohydrates like G3P (three-carbon sugar).
• These carbohydrates create other organic molecules plants require for growth and energy.

Structure of a Leaf

• Leaves contain mesophyll cells, epidermal cells, and vascular bundles.
• Mesophyll cells, in the leaf's middle, have many chloroplasts.
• Chloroplasts are the organelles housing photosynthesis.
• They contain pigments that capture light energy.
• Chloroplast pigments make the cells green.

Mechanism of Photosynthesis

• Light reactions occur in thylakoid membranes within chloroplasts.
• Light energy forms ATP and NADPH from ADP and NADP+.
  • Light excites electrons in chlorophyll.
  • Electrons move through an electron transport chain.
  • A proton gradient is created across the thylakoid membrane.
  • ATP synthase produces ATP from ADP and inorganic phosphate.
  • Electrons reduce NADP+ to form NADPH.
  • ATP and NADPH are used in the Calvin cycle to synthesize carbohydrates.
• Water molecules split, releasing oxygen into the atmosphere.
• The Calvin cycle happens in the stroma of the chloroplasts.
• It uses ATP and NADPH to combine carbon dioxide with organic molecules, forming new molecules like G3P.
• ADP and NADP+ are recycled for light reactions.
• The Calvin cycle uses ATP and NADPH generated from light reactions.
  • Carbon dioxide combines with RuBP, catalyzed by rubisco.
  • The reaction yields two 3-PGA molecules.
  • ATP provides energy, while NADPH converts 3-PGA into G3P.
  • G3P regenerates RuBP and forms carbohydrates.

Detailed Steps of Light Reactions

• Photosystems I and II are protein-pigment complexes that absorb light and excite electrons.
• Excited electrons create a proton gradient as they move through the electron transport chain.
• ATP synthase uses the proton gradient to synthesize ATP from ADP and inorganic phosphate.
• Electrons interact with NADP+ to form NADPH, storing light energy.

Detailed Steps of the Calvin Cycle

• Phase 1: Carbon Fixation
  • Carbon dioxide reacts with ribulose bisphosphate (RuBP), incorporating it into organic molecules.
  • Rubisco catalyzes this reaction, producing 3-PGA molecules.
• Phase 2: Reduction
  • ATP and NADPH convert 3-PGA molecules into G3P.
  • One G3P molecule exits the cycle for organic molecule formation.
• Phase 3: Regeneration
  • The remaining G3P molecules regenerate RuBP, allowing the cycle to continue, requiring additional ATP.

Significance of Photosynthesis

• Photosynthesis produces around 150 billion metric tons of carbohydrates annually.
• It generates atmospheric oxygen, vital for life on Earth.
• Photosynthesis fuels plant growth by providing organic molecules.
• Leaf cells produce sucrose and starch, transported for energy storage and use.

Conclusion: Summary of Photosynthesis

• Photosynthesis converts solar energy into chemical energy, involving light reactions and the Calvin cycle.
• It produces carbohydrates and oxygen.
• This process sustains life by providing energy and oxygen.