chapter 6

  • metabolism is the totality of an organism’s chemical reactions

  • a metabolic pathway begins with a specific molecule and ends with a product

    • the steps of a metabolic pathway are catalyzed by specific enzymes

    • catabolic pathways break down

    • anabolic pathways build up

  • kinetic, thermal, potential, and chemical energy

    • energy can be converted from one form to another

  • organisms are open systems

    • open systems are systems in which energy and matter can be transferred between the system and its surroundings

  • laws of thermodynamics:

    • 1st - energy can be transferred and transformed, but it can never be created or destroyed

    • 2nd - every energy transfer or transformation increases the entropy of the universe

  • spontaneous processes must increase entropy of the universe

    • if a process decreases the entropy of the universe (unfavorable), it is nonspontaneous and can only occur if energy is provided to the system

  • free energy is energy that can do work when temperature and pressure are uniform

    • ΔG = ΔH - TΔS

      • ΔH: change in enthalpy

      • T: temperature in kelvins

      • ΔS: change in entropy

    • if ΔG is negative, the process is spontaneous

    • ΔG positive or zero, the process is nonspontaneous

    • the lower ΔG is, the more stable the system is

  • equilibrium = max stability

    • a process is spontaneous and can perform work only if it is moving toward equilibrium

  • exergonic reaction: proceeds with a net release of free energy & is spontaneous

  • endergonic reaction: absorbs free energy from its surroundings & is non spontaneous

  • all reactions in a closed system eventually reach equilibrium

    • cells are open systems, never to be in equilibrium

  • ATP is broken by hydrolysis to release energy

  • cells do three types of work: chemical, transport, and mechanical. all are powered by ATP hydrolysis

  • energy coupling: the use of an exergonic process to drive an endergonic one

    • ATP hydrolysis is exergonic, so that process drives an endergonic process

    • ATP hydrolysis leads to a change in protein shape and binding ability

  • phosphorylation is transferring a phosphate group from ATP to another molecule to create a phosphorylated intermediate

  • activation energy is the energy needed to start a chemical reaction

    • usually absorbed in the form of thermal energy

  • enzymes speed up reactions by lowering activation energy

    • enzymes lower activation energy by:

      • orienting substrates correctly

      • straining substrate bonds

      • providing a favorable microenvironment

      • covalently bonding to the substrate

    • they do not affect free energy, since they only speed up reactions that would occur

  • induced fit of a substrate brings chemical groups of the active site into positions that enhance their ability to catalyze the reaction

  • another way to increase the rate of an enzyme-catalyzed reaction can be to increase substrate concentration until saturation is reached

    • when all enzyme molecules are occupied, the enzyme is saturated

    • after saturation, the only way to increase the reaction rate is to add more enzyme

  • enzyme rates are affected by temperature, pH, chemicals, etc

    • optimal temperatures and pH are favorable

  • cofactors: nonprotein enzyme helpers

    • inorganic (metal/ionic)

    • organic (coenzymes)

      • coenzymes like vitamins

  • inhibitors:

    • competitive inhibitors bind to the active site to compete with the substrate

    • noncompetitive inhibitors bind to another part of the enzyme to force the enzyme to change shape

  • regulation of enzyme activity:

    • allosteric regulation

      • NON COMPETITIVE INHIBITORS

      • either inhibits or stimulates an enzymes activity

      • occurs when a regulatory molecule binds to a protein at one site and affects the protein’s function at another site

      • every enzyme complex has active and inactive forms

        • the binding of an activator stabilizes the active form of the enzyme

        • the binding of an inhibitor stabilizes the inactive form of the enzyme

      • cooperativity is a form of allosteric regulation that can amplify enzyme activity

    • feedback inhibition

      • when the end product of a metabolic pathway shuts it down

      • prevents a cell from wasting more resources by synthesizing more product than needed

  • POSITIVE/NEGATIVE DELTA G CAN ONLY INDICATE IF THE REACTION IS EXERGONIC/ENDERGONIC, NOT EXOTHERMIC/ENDOTHERMIC

  • rna is most similar to atp by structure