Cells and Energy Flow

Cells and Energy Flow

• Energy is the capacity to perform work or cause alterations.
• Kinetic energy is energy of motion, like water moving over a waterfall.
• Potential energy is stored energy, such as chemical energy found in food.
• Energy flows, it doesn't cycle.

Laws of Thermodynamics

• Energy Law of Conservation: Energy can change form but cannot be created or destroyed, such as in photosynthesis.
• The Law of Entropy: Energy transformation is never 100% efficient, and usable energy is lost.
• Energy transformation makes the universe less organized, with disorder increasing.
• Producers use energy to generate organized structures in biological molecules.
• Organisms depend on solar energy for survival.

Cells and Entropy

• Cellular processes transform energy and increase entropy in the universe.
• Increased entropy reduces available energy for work.
• Glucose tends to degrade into carbon dioxide and water.
• Glucose is more organized but less stable than its breakdown products.
• Energy from photosynthesis (sun) is used to create glucose from carbon dioxide and water.

Metabolism and Energy Transformations

• Metabolism is the compilation of chemical reactions that occur in a cell.
• Free energy (delta G) is the amount of energy remaining to execute work post-chemical reaction.
• Exergonic Reactions have a negative delta G (< 0), are spontaneous, release energy, and have less free energy in the products than reactants.
• Endergonic Reactions have a positive delta G (> 0), are non-spontaneous, require energy, and have more free energy in the products than reactants.

ATP: Energy Currency

• ATP is an unstable molecule with high potential energy.
• ATP is a nucleotide composed of adenine, ribose sugar (adenosine), and three phosphate groups.
• ATP supplies energy for:
  • Chemical work: synthesizing macromolecules
  • Transport work: pumping substances across membranes
  • Mechanical work: muscle contraction, movement of cilia and flagella.
• ATP is not stored in cells.
• ATP captures energy from exergonic reactions.
• ATP acts as a chemical energy carrier for endergonic reactions.
• Cells can couple ATP hydrolysis to energy-requiring reactions in two ways:
  • ATP energizes a reactant.
  • ATP changes the shape of a reactant.
• The hydrolysis of ATP releases stored energy, which allows changes in the amount of free energy to complete work.
• Hydrolysis of ATP has negative delta G.
• Examples of ATP hydrolysis: protein synthesis, nerve conduction, and muscle contraction

Metabolic Pathways and Enzymes

• Reactions typically occur in a sequence.
• A Metabolic pathway is a series of linked reactions.
• A metabolic pathway
  • Begins with a specific reactant, proceeds through intermediates, and ends with a specific end product.
  • A = Initial Reactant/Substrate
  • B, C, D, E, and F = Intermediates
  • G = End Product.
• Enzymes are protein catalysts.
• Substrates are reactants in an enzymatically catalyzed reaction.
• Each enzyme accelerates a specific reaction.
• Each reaction in a metabolic pathway needs a unique, specific enzyme.
• The end product will not form unless all pathway enzymes are present and functional.
• Active site is the part of an enzyme that is complexes with substrate.
• An active site causes enzymes to change shapes.
• In the Induced fit Model, the enzyme changes shape slightly to fit the substrate.
• After the reaction is complete, the product is released and the enzyme returns to its original shape.
• Energy of Activation is the added energy needed for molecules to react together.
• EA prevents spontaneous molecule degradation within the cell.
• Enzymes lower the energy of activation by bringing the substrates into contact, speeding up reactions.

Factors Affecting Enzymatic Rate

• Substrate Concentration: Increased substrate concentration increases enzyme activity due to frequent collisions between substrate molecules and the enzyme.
• Temperature:
  • Increased temperature increases enzyme activity.
  • Warmer temperatures cause more effective collisions between enzyme and substrate.
  • High temperatures can denature and destroy enzymes.
• pH:
  • Enzymes have an optimal pH for reaction rate.
  • pH changes alter enzyme shapes and reduce enzymatic speed.
  • Extreme pHs denature enzymes.
• Enzyme Cofactors are molecules required to activate enzymes.
  • FAD, NAD⁺, and NADP⁺ are cofactors involved in cellular respiration and photosynthesis.
  • Coenzymes are nonprotein organic molecules.
• Vitamins are organic compounds for coenzyme synthesis.
• Enzyme Inhibition: Inhibitors decrease enzyme activity.
  • Competitive inhibition involves the substrate and inhibitor competing for the active site.
  • Noncompetitive inhibition involves the inhibitor binding to an allosteric site, not the active site.

Oxidation-Reduction (Redox) Reactions

• Electrons transfer from one molecule to another.
• Oxidation – loss of an electron
• Reduction – gain of an electron
• Oxidation and reduction occur simultaneously.
• One molecule (or atom) accepts the electron given up by the other.
• Example: Sodium is oxidized and chlorine is reduced to produce NaCl.
• OILRIG = oxidation is loss, reduction is gain.

Photosynthesis and Cellular Respiration

• Photosynthesis: 6CO₂ + 6H₂O + energy → C₆H₁₂O₆ + 6O₂. Carbon dioxide is reduced and water is oxidized.
• Cellular Respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy. Glucose is oxidized, and oxygen is reduced.
• Chloroplasts capture solar energy to convert water and carbon dioxide into carbohydrates.
• Hydrogen atoms are transferred from water to carbon dioxide as glucose forms.
• The reduction of carbon dioxide to form glucose stores 686 kilocalories of energy.
• Photosynthesis involves the coenzyme NADP⁺: NADP⁺ + 2e⁻ + H⁺ → NADPH.
• Mitochondria oxidize carbohydrates and use the released energy to build ATP.
• Cellular respiration consumes oxygen and produces carbon dioxide.
• Glucose is oxidized, and oxygen is reduced in cellular respiration.
• When oxygen gains hydrogen atoms, water is created.
• Cells oxidize glucose stepwise, and create energy.
• Cellular respiration involves the coenzyme NAD⁺: NAD⁺ + 2e⁻ + H⁺ → NADH.