POB6--How Cells Use Energy

CH 5: HOW CELLS USE ENERGY

The Flow of Energy in Living Cells

• Energy is the ability to do work.

• Two states of energy:

  • Kinetic Energy: Energy of motion.

  • Potential Energy: Stored energy for future use.

• Living organisms transform potential energy into kinetic energy for work.

The Flow of Energy in Living Things

• Various forms of energy can be converted to heat energy, a measurable form.

• Thermodynamics: Study of energy heat changes.

The Laws of Thermodynamics

• 1st Law: Energy in the universe is constant; it can change forms but not be created/destroyed. Some energy is lost as heat.

• 2nd Law: Entropy (disorder) in the universe increases; thus energy transforms from potential to heat energy.

Theme – Flow of Energy in Living Things

• Organisms (e.g., plants) capture solar energy to build molecules, which store potential energy.

• Higher-level organisms metabolize these food molecules for energy.

• Chemical reactions involve making and breaking of chemical bonds.

Chemical Reactions

• Reactants/Substrates: Starting molecules in a chemical reaction.

• Products: Molecules resulting from the reaction.

• Types of Reactions:

  • Endergonic: Products have more energy (non-spontaneous).

  • Exergonic: Products have less energy (spontaneous).

• Activation Energy: Initial energy needed to start a reaction. Catalysts lower activation energy and speed up reactions.

How Enzymes Work

• Enzymes: Catalysts in cells that lower activation energy by stressing bonds in substrates.

• Active Site: Location on enzyme where substrate binds; binding causes shape change leading to an "induced fit", forming an enzyme-substrate complex.

• Enzymes can be reused after a reaction.

Enzyme Activity Regulation

• Enzyme shape can be altered for regulation:

  • Allosteric Enzymes

    • Activators: Change shape for active site opening.

    • Repressors: Bind and inhibit the enzyme.

• Feedback Inhibition: Product acts as a repressor; can be competitive (blocks active site) or non-competitive (affects allosteric site).

ATP—The “Batteries” of the Cell

• ATP (Adenosine Triphosphate): Energy currency of the cell.

• Structure: Sugar, adenine nucleotide, three phosphate groups.

• Energy released when ATP breaks down to ADP + Pi.

• Coupled Reactions: Exergonic reactions provide energy for endergonic reactions, often through ATP breakdown.

• ATP is recycled in photosynthesis and cellular respiration.

Other Ways to Transfer Energy: Electrons

• Redox Reactions: Involve transfer of electrons.

  • Oxidation: Loss of electrons.

  • Reduction: Gain of electrons.

• These reactions involve energy transfer with reduced forms having higher energy.

Inquiry & Analysis

• Key questions: Is there a saturation effect? Do enzymes physically bind to substrates?