METABOLISM Chapter 8

Energy of Life  Metabolism is the combination of all the chemical reactions in an organism  Arises from interactions of molecules within an orderly cell  Facilitated by metabolic pathways which are altered series of steps that create new products  Often catalyzed by enzymes  Balances supply and demand of the cell (think traffic lights)

Types of Metabolic Pathways  Catabolic (C A + B)  Release energy by breaking down complex molecules into simpler ones; degradation  E.g cellular respiration: fuels and O 2 to energy, H 2 0, and CO 2  Anabolic (A + B C)  Use energy to make more complex molecules by consuming simpler ones; biosynthetic  E.g amino acids to form proteins  Energy from catabolic (downhill) reactions can be stored to drive anabolic (uphill) ones

A Review of Energy  The capacity to cause change or rearrange matter; to do work  KE is energy of movement or objects in motion Thermal energy (heat) is KE from random movement of atoms or molecules  PE is stored energy; energy due to structure or location Chemical energy is the PE available for release in a chemical reaction  Necessary for all metabolic processes  Organisms are energy transformers  Energy forms include: heat, light, and sound

Energy Moves Around  Energy enters the world (light E)  Sunlight is the ultimate source of all energy  Harnessed or captured by plants (converts to chemical E)  Photosynthesis produces sugars stored in plants  Energy transfer between organisms (converts to kinetic E)  Organisms that consume plants can use for metabolism Some lost as heat  Energy transfer again  Organisms that eat what ate plants

Thermodynamics  1st Law of Thermodynamics  Energy can not be created or destroyed, it is transferred or transformed  2 nd Law of Thermodynamics  During conversion of energy from one form to another, some is lost as heat Makes universe more disorderly An input of energy is needed to maintain order

Order vs. Disorder  Living systems create ordered structures from less ordered starting materials  Amino acids ordered into polypeptide chains  Living organisms are organized and complex  Take in ordered forms of matter and energy and replace them with less ordered forms  Consume food to catabolize into CO 2 and H 2 0  Organisms’ orderly state converted to disorder upon death

Classifying Reactions  Net release of energy  Magnitude is max work that can be done  Are spontaneous, no energy needed  Absorbs free energy  Magnitude is energy needed to drive reaction  Stores free energy, nonspontaneous Exergonic: ‘energy outward’Endergonic: ‘energy inward’

Metabolic Equilibrium  Matter that doesn’t interact with environment will reach equilibrium and stop reacting  Cell at metabolic equilibrium is dead (can’t work)  Cells maintain constant flow of materials in and out of cell  Keeps metabolic pathways from reaching equilibrium  Continues if product don’t accumulate C 6 H 12 O 6 and O 2 available and ways to excrete waste ≠ equilibrium

Energy Coupling  Use exergonic processes to drive endergonic  ATP mediates most processes  Immediate source of energy to power cellular work  3 main types of cellular work  Chemical: endergonic reactions, synthesizing polymers  Transport: pumping substances across membrane against [gradient]  Mechanical: beating of cilia or contraction of muscle cells

Adenosine Triphosphate (ATP)  Nucleotide consisting of sugar ribose, nitrogenous base adenine, and 3 phosphate groups  Bonds can be hydrolyzed  ATP ADP + P i + E Exergonic: -7.3 kcal/mol  Phosphate groups have (-) charge grouped together  Repulsion like a spring

Hydrolysis of ATP  Can heat cells when sole reaction  Shivering to generate heat from muscle contraction = inefficent  Proteins actually harness E to perform cellular work  Use exergonic to drive endergonic reactions  Involves transfer of P i from ATP to another molecule, called phosphorylation Molecule becomes more reactive  Can change protein shape and binding

Activation Energy (E A )  Amount of energy needed to ‘push’ reactants toward products  Barrier that determines the rate of a reaction  Enzymes, proteins that act as catalysts, act to lower E A so reactions occur faster Often end in ‘-ase’ Reaction specific  Reactants absorb E until unstable, allowing bonds to break

Enzyme Activity * Specific to a substrate, based on 3D shape

Enzyme Function Effects  Temperature: increase rate b/c molecules move faster  To a point, above will denature  pH: optimal 6-8, but exceptions exist (pepsin and trypsin)  Cofactors/coenzymes: inorganic or organic helpers  i.e. vitamins  Inhibitors: weak bonds = reversible, covalent bonds aren’t  Competitive inhibitors: prevents substrate from binding to active site b/c binds first or stronger (CO vs O 2 )  Counter by increasing substrate  Non-competitive inhibitors: binds to an alternate spot and changes active site so intended substrate can’t bind  i.e. sarin gas and DDT