Cellular Energetics Summary

Enzymes have an active site that interacts with substrate molecules (ENE-1.D).
The shape and charge of the substrate must be compatible with the active site for a reaction to occur.

Enzymes are biological catalysts that lower activation energy, facilitating chemical reactions (ENE-1.E).

Changes to enzyme structure can alter its function or efficiency (ENE-1.F).
Denaturation disrupts protein structure, eliminating the ability to catalyze reactions.
Non-optimal environmental temperatures and pH can alter enzyme structure and efficiency.
Enzyme denaturation can be reversible in some cases.
Environmental pH affects enzyme activity, possibly disrupting hydrogen bonds (ENE-1.G).
$pH = -log[H+]$ (understanding concepts is important, calculations are not).
Substrate and product concentrations affect enzymatic reaction efficiency.
Higher temperatures increase molecular movement and collision frequency, increasing reaction rate.
Competitive inhibitors can bind reversibly to the active site.
Noncompetitive inhibitors bind to allosteric sites, changing enzyme activity.

Living systems require constant energy input (ENE-1.H).
Life requires a highly ordered system and adheres to the second law of thermodynamics.
Energy input must exceed energy loss to maintain order and power cellular processes.
Energy-releasing processes can be coupled with energy-requiring processes.
Loss of order or energy flow results in death.
Energy-related pathways are sequential for controlled and efficient energy transfer.
A product of one reaction becomes the reactant for the next in a metabolic pathway.

Organisms capture and store energy through photosynthesis (ENE-1.I).
Photosynthesis uses sunlight to produces sugars.
Prokaryotic photosynthesis oxygenated the atmosphere.
Prokaryotic pathways were the foundation for eukaryotic photosynthesis.
Light-dependent reactions yield ATP and NADPH (ENE-1.J).
Chlorophyll absorbs light energy, boosting electrons in photosystems I and II.
Electron transport chain (ETC) connects photosystems I and II.
Electron transfer through the ETC establishes a proton gradient across the internal membrane.
ATP is synthesized from ADP and inorganic phosphate via ATP synthase.
ATP and NADPH power carbohydrate production from carbon dioxide in the Calvin cycle.

Fermentation and cellular respiration use energy from biological macromolecules to produce ATP (ENE-1.K).
Cellular respiration involves enzyme-catalyzed reactions that capture energy.
The electron transport chain transfers energy, establishing an electrochemical gradient.
ETC reactions occur in chloroplasts, mitochondria, and prokaryotic plasma membranes.
Electrons from NADH and FADH2 are passed to electron acceptors, with oxygen as the terminal acceptor in cellular respiration.
A proton gradient forms across the inner mitochondrial membrane or chloroplast membrane.
Chemiosmosis drives ATP formation via ATP synthase (oxidative phosphorylation in cellular respiration, photophosphorylation in photosynthesis).
Oxidative phosphorylation generates heat, used by endotherms to regulate body temperature.
Glycolysis releases energy from glucose, forming ATP, NADH, and pyruvate (ENE-1.L).
Pyruvate is transported to the mitochondrion for further oxidation.
The Krebs cycle releases carbon dioxide, synthesizes ATP, and transfers electrons to NADH and FADH2.
Electrons from glycolysis and the Krebs cycle are transferred to the electron transport chain.
An electrochemical gradient of protons is established across the inner mitochondrial membrane.
Fermentation allows glycolysis to proceed without oxygen, producing organic molecules (e.g., alcohol, lactic acid).
ATP to ADP conversion releases energy for metabolic processes.

Molecular variation enables organisms to respond to environmental stimuli (SYI-3.A).
Variation in the number and types of molecules increases the ability to survive and reproduce.