Chapter 5 The Working Cell

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					Chapter 5: The Working Cell
   Energy and the Cell
   Energy
          o Capacity to perform work
          o Work performed when an object is moved against opposing force
          o Capacity to rearrange matter
   Kinetic energy
          o Energy of motion
          o Moving objects perform work by transferring motion to other matter
          o Heat
                  Thermal energy
                  Form of KE
                  Movement of molecules or atoms in a body of matter
   Potential Energy
          o Stored energy
          o Depends on location of structure
          o Electrons have PE because of position in electron shells
   Chemical energy
          o PE of molecules
          o Most important type of energy in living organisms
          o Can be released to power work of cell
   Thermodynamics
          o Study of energy transformations that occur in a collection of matter
   System
          o Matter under study
   Surroundings
          o Everything outside of the system
   Open system
          o Living organism
          o Exchanges energy and matter with surrounds
   First law of Thermodynamics
          o Law of conservation of energy
          o Energy can be transferred and transformed but can not be destroyed
   Second law of thermodynamics
          o Entropy
                  Amount of disorder in a system
          o Energy conversions reduce the order of the universe, thus increasing the
             entropy
   Endergonic reactions
          o Require a net input of energy
          o Yield product with a lot of PE
          o Reactants have low PE, products have high
   Exergonic reaction
          o Releases energy
          o Reactants have more energy in the covalent then do their products
        o Releases amount of energy equal to the difference in PE between reactants
           and products
   Cellular respiration
        o Uses oxygen to convert chemical energy stored in fuel molecules to
           chemical energy used to perform work
        o Takes several steps unlike burning
        o Some energy escapes as heat but most converted to chemical energy of
           ATP
   Cellular Metabolism
        o Sum of endergonic and exergonic reaction
   Energy coupling
        o Use of energy released from exergonic reactions to drive essential
           endergonic reactions
        o ATP is the key
   5.4: ATP shuttles chemical energy and drives cellular work
   ATP
        o Powers almost all forms of cellular work
        o Adenosine triphosphate
        o Like charges of phosphates are crowded together and mutual repulsion
           contributes to PE stored in ATP




        o Bonds in ATP are unstable and are thus easily broken
        o One phosphate leaves creating ADP, releasing energy
   Phosphorylation
        o Transferring a phosphate group from ATP to some other molecule making
           an endergonic reaction
        o Cellular work depends on ATP energizing molecules by phosphorylating
           them
   Cellular work
        o Chemical work
                Phosphorylation of reactant molecules drives the energonic
                   synthesis of product molecules
        o Mechanical work
        o Transport work
   How enzymes function
   5.5: Enzymes speed up the cell’s chemical rxns by lowering energy barriers
   Energy of activation (EA)
        o Energy barrier
        o Amount of energy that reactants must absorb to become activated to start a
           chemical reaction
   Enzyme
        o Protein molecule that functions as a biological catalyst
        o Increases the rate of a reaction without itself being changed into a different
            molecule
        o Speeds up reaction by lowering EA barrier
        o Does not add energy
   5.6: A specific enzyme catalyzes each cellular reaction
   Substrate
        o Specific reactant that an enzyme acts on is substrate of the enzyme
        o Fit into a region of enzyme called active site
                 Active site
                         Pocket or groove on surface of enzyme
                         Only fits one kind of substrate molecule so is specific
   Induced fit
        o Active site changes shape slightly so that it embraces substrate
        o May strain substrate bonds or place chemical groups of active site in
            position to catalyze reaction
   5.7: The cellular environment affects enzyme activity
   Affect of temperature on enzyme activity
        o Affects molecular motion
        o Enzyme’s optimal temperature produces the highest rate of contact
            between reactant molecules and the enzyme’s active site
        o higher temperatures denature the enzyme, destroying its function
   Salt concentration and pH
        o Few enzymes tolerate extremely salty solutions
        o Same for extra hydrogen ions at very low pH
        o Optimal pH for enzymes is 6-8
   Cofactors
        o Nonprotein helpers
        o Inorganic substances
   Coenzyme
        o Cofactor that is an organic molecule
   5.8: Enzyme inhibitors block enzyme action




   Inhibitor
        o A chemical that interferes with an enzyme’s activity
   Competitive inhibitor
        o Resembles the enzyme’s normal substrate and competes with the substrate
            for the active site on the enzyme
        o Reduces the productivity of an enzyme by blocking the substrates from
            entering the active site
        o Can be overcome by increasing the concentration of substrate molecules,
            making it more likely that a substrate molecule will be nearby when an
            active site opens up
   Noncompetitive inhibitor
        o Does not enter the active site
        o Binds to enzyme somewhere else thus changing the shape of the enzyme
            so that the active site no longer fits the substrate
   Feedback inhibition
        o A metabolic reaction is blocked by its products
        o Important mechanism in regulated metabolism
   5.9: Many Poisons, pesticides, and drugs are enzymes inhibitors
   Cyanide
        o Poison that inhibits an enzyme involved with the production of ATP
            during cellular respiration
   Penicillin
        o Inhibits an enzyme that bacteria use in making cell walls
        o Because we lack enzyme, not affected by drug
   Membrane structure and function
   5.10: Membranes organize the chemical activities of cells
   Membranes
        o Provide structural basis for metabolic order
        o In eukaryotes, membranes form most of the cell’s organelles
        o Partition cell into functional compartments that contain specific enzymes
        o Boundary between living cell and surroundings
   Selective permeability
        o Allows some substances to cross more easily than others
        o Ex. Plasma membrane
   5.11: Membrane phospholipids form a bilayer




   Phospholipids
       o Main structural components of membranes
       o Phosphate group and two fatty acids
       o Head is hydrophilic
       o Tail is nonpolar, hydrophobic
       o Form two layer sheet, bilayer
       o Hydrophobic molecules pass through membranes (lipid soluble)
       o Hydrophilic depend on protein molecules in bilayer to determine whether
          pass through membrane
   5.12: The membrane is a fluid mosaic of phospholipids and proteins




   Fluid mosaic
        o Mosaic is surface made of small fragments
        o Diverse protein molecules embedded in framework of phospholipids
        o Most of individual proteins and phospholipid molecules drift in membrane
   Keeping the membrane fluid
        o Kink tails of phospholipids
        o Cholesterol
   5.13: Proteins make the membrane a mosaic of function
   Proteins
        o Perform most of the functions of a membrane
                 Attaching membrane to the cytoskeleton and external fibers
                 Providing identification tags
                 Forming junctions between adjacent cells
                 Transport things across membrane
                         Passive
                              o Going with diffusion
                              o No energy expense
                         Active
                              o Going against diffusion
                              o Uses ATP
   Receptors
        o Chemical messengers from other cells
        o Has shape that firs shape of specific messenger
   Signal transduction
        o Binding of messenger to receptor triggers chain reaction involving other
            proteins
                 Relay message to a molecule that performs specific activity in the
                   cell
   5.14: Passive transport is diffusion across a membrane
   Diffusion
        o Tendency for particles of any kind to spread out evenly in an available
            space
        o High concentrationLow concentration
        o Requires no work
        o Results from random motion of atoms and molecules
        o
   Concentration gradient
        o Both sides have equal concentration
        o Diffuses down concentration gradient until equilibrium is reached
        o Equilibrium
                 No net change in concentration on either side of the membrane
   Passive transport
        o Diffusion of a substance across biological membrane
        o Ex. O2 in, CO2 out in lungs, red blood cells
   5.15: Transport proteins may be facilitate diffusion across membranes
   Facilitated diffusion
        o One of the proteins makes it possible for a substance to move down its
            concentration gradient
        o Depends on the number of transport protein molecules for a particular
            substance present in the membrane

				
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