Living Systems & Thermodynamics

• Living systems require constant energy input and macromolecule exchange.
• Free energy is needed for homeostasis and cellular functions; lack of it increases entropy, leading to cellular dysfunction and death.

Thermodynamics

• Organisms that get less free energy than required lose homeostasis, cellular processes fail, and they may die.
• The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or transformed.
• The second law of thermodynamics states that energy transfers increase entropy, with some energy lost as heat.
• Cellular respiration is a process that releases energy.
• Released energy can be coupled to processes like active transport or protein synthesis.
• Earth gets constant free energy from the Sun, which plants convert to chemical energy.
• Heterotrophs get free energy by consuming and breaking down organic molecules in cellular respiration.

Photosynthesis Overview

• Photosynthesis has two stages: light-dependent reactions and the Calvin cycle.
• Light-dependent reactions (in the thylakoid membrane) use sunlight to split water, producing ATP, NADPH, and oxygen.
• The Calvin cycle (in the stroma) uses ATP and NADPH to convert CO2 into glucose.
• Organisms capture and store energy for biological processes.
• Photosynthesis captures solar energy and produces sugars.
• Light-dependent reactions involve pathways that capture light energy to yield ATP and NADPH, powering organic molecule production.

Photosynthesis Details

• Chlorophyll absorbs light energy, boosting electrons to a higher energy level in photosystems I and II.
• Photosystems I and II are in chloroplast internal membranes and connected by an electron transport chain (ETC).
• Electrons transferred between molecules in the ETC create a proton electrochemical gradient across the internal membrane.
• ATP synthase: enzyme that protons pass through
• The final electron acceptor is NADP+, which becomes NADPH.
• Electrons come from water, which splits in photolysis, releasing oxygen (O2).
• Light-independent reactions (Calvin cycle) occur in the stroma.
• The ultimate product of the light-independent reaction is glucose (C6H12O6).
• Carbon atoms come from atmospheric CO2, which enters the Calvin cycle.

Cellular Respiration Overview

• Fermentation and cellular respiration use energy from biological macromolecules to produce ATP.
• Cellular respiration in eukaryotes are enzyme-catalyzed reactions that capture energy from macromolecules.
• The formation of the proton gradient is linked to ATP synthesis from ADP and inorganic phosphate via ATP synthase.
• Energy captured in light reactions and transferred to ATP and NADPH powers carbohydrate production from carbon dioxide in the Calvin cycle (in the chloroplast stroma).
• Glycolysis releases energy in glucose to form ATP, NADH, and pyruvate.
• Pyruvate is transported to the mitochondrion for further oxidation.

Cellular Respiration Details

• In the Krebs cycle, organic intermediates release carbon dioxide, ATP synthesizes from ADP and inorganic phosphate, and electrons transfer to NADH and FADH2.
• NADH and FADH2 transfer electrons extracted in glycolysis and Krebs cycle reactions to the electron transport chain in the inner mitochondrial membrane.
• Electron transfer through the ETC establishes a proton electrochemical gradient across the inner mitochondrial membrane.
• Fermentation allows glycolysis without oxygen, producing organic waste molecules like alcohol and lactic acid.
• ATP-to-ADP conversion releases energy to power processes.
• The electron transport chain transfers energy from electrons in coupled reactions, establishing an electrochemical gradient.
• Electron transport chain reactions happen in chloroplasts, mitochondria, and prokaryotic plasma membranes.
• In cellular respiration, NADH and FADH deliver electrons, passing them to electron acceptors, moving toward the terminal electron acceptor, oxygen.
• Aerobic prokaryotes use oxygen as a terminal electron acceptor; anaerobic ones use other molecules.
• Proton transfer accompanies electron transfer forms a proton gradient across the inner mitochondrial membrane (or internal membrane of chloroplasts).
• Membrane(s) separate a high proton concentration region from a low proton concentration region.

Glycolysis and Fermentation

• Glycolysis begins with glucose, producing ATP, NADH, and pyruvate.
• If oxygen is available, pyruvate enters the mitochondria for aerobic respiration; otherwise, it undergoes fermentation.
• Glycolysis is “highly conserved” across life, suggesting its early evolution before complex organelles.
• Glycolysis in the cytoplasm supports this theory because it does not require membrane-bound organelles.
• The Krebs cycle's purpose is to produce energy carriers (NADH and FADH2) and ATP while releasing CO2.
• The Krebs cycle makes NADH, FADH2, and ATP; NADH and FADH2 go to the ETC, carrying high-energy electrons.
• Aerobic fermentation produces CO2
• During electron transport, protons pump into the intermembrane space, establishing an electrochemical gradient, making the space acidic
• Protons flow back across the membrane through ATP synthase in chemiosmosis, making ATP by joining ATP and inorganic phosphate in oxidative phosphorylation.

Additional Notes

• Phosphorylation: the addition of a phosphate group to a molecule, often to store or transfer energy.
• Some prokaryotes have Electron Transport Chains but don't have mitochondria or chloroplasts.
• During Fermentation, pyruvate (end product of Glycolysis is converted to Lactic Acid or Alcohol.
• Endotherms use heat from cellular respiration, especially from the ETC, to regulate their body temperature.
• Mitochondria needs O2 and Glucose; produces CO2
• Different chlorophylls provide the plant with a greater ability to use light for photosynthesis
• Plants have chlorophyll a (425nM & 675nM) and chlorophyll b (475nM & 625nM)
• Variation in chlorophyll types results in a greater ability to absorb energy, which in turn can lead to doing more photosynthesis.