Chapter 5

• Cells control their chemical environment using energy, enzymes, and the plasma membrane
• Energy


  The capacity to cause change or the ability to do work
• Kinetic energy


  The energy of motion
• Potential energy


  Stored energy, energy that an object has because of its location or structure
• Chemical energy


  Stored in molecules based on the arrangement of atoms, can be released by a chemical reaction
• Cellular respiration


  The energy-releasing chemical breakdown of fuel molecules, the storage of that energy in a form the cell can use to perform work
• ATP


  Acts like an energy shuttle, stores energy obtained from food, releases it later as needed
• ATP (adenosine triphosphate)


  Consists of an organic molecule called adenosine plus a tail of three phosphate groups, is broken down to ADP and a phosphate group releasing energy
• The ATP-ADP cycle


  Cellular work spends ATP continuously, ATP is recycled from ADP and a phosphate group through cellular respiration
• A working muscle cell spends and recycles up to 10 million ATP molecules per second
• Phosphate transfer


  ATP energizes other molecules by transferring phosphate groups, this energy helps cells perform mechanical work, transport work, and chemical work
• Metabolism


  The total of all chemical reactions in an organism
• Enzymes


  Proteins that speed up chemical reactions
• All living cells contain thousands of different enzymes, each promoting a different chemical reaction
• Enzymes


  Reduce the amount of activation energy required to break bonds of reactant molecules
• Induced fit


  The interaction where the entry of the substrate induces the enzyme to change shape slightly
• Enzyme inhibitors


  Can prevent metabolic reactions by binding to the active site or near the active site, resulting in changes to the enzyme's shape so that the active site no longer accepts the substrate
• Feedback regulation


  When products of a reaction may inhibit the enzyme required for its production, preventing the cell from wasting resources
• Passive transport


  The diffusion of a substance across a membrane without the input of energy
• Concentration gradient


  A region in which the substance's density changes
• Simple diffusion


  The diffusion of substances that are small and nonpolar
• Facilitated diffusion


  The passage of a substance that can't diffuse on its own with the help of a protein
• Osmosis


  The diffusion of water across a selectively permeable membrane
• Hypertonic solution


  A solution with a higher concentration of solute
• Hypotonic solution


  A solution with a lower concentration of solute
• Isotonic solution


  A solution with an equal concentration of solute
• Active transport


  Requires that a cell use energy to move molecules across a membrane
• Exocytosis


  The secretion of large molecules within transport vesicles
• Endocytosis


  Takes material in via vesicles that bud inward from the plasma membrane