UNIT III: CELLULAR ENERGETICS
A.Bioenergetics
➢ Glucose, starch, and fat all energy-rich, but the bonds must be broken in order for the energy to
be released
➢ First Law of Thermodynamics: Energy cannot be created or destroyed. The sum of energy in
the universe is constant.
➢ Second Law of Thermodynamics: Energy transfer leads to less and less organization. The
universe tends toward entropy
➢ Types of Reactions
○ Exergonic
■ Products have less energy than the reactants
■ Energy is given off during the reaction
■ Ex. oxidation of molecules in mitochondria
○ Endergonic
■ Require an input of energy
■ Products have more energy than reactants
■ Ex. plants’ use of CO2 and water to form sugars
, B. Gibbs Free Energy
➢ ΔG=ΔH-TΔS
○ T=temperature
○ H=enthalpy (measure of energy in a thermodynamic system)
○ S=entropy
○ Change in the Gibbs free energy of a reaction determines whether the reaction in
favorable (spontaneous, negative) or unfavorable (nonspontaneous, positive)
○ Used to figure out if, without adding energy, the reactants will stay as they re or be
converted to products
➢ Spontaneous Reactions
○ Occur without a net addition of energy
○ ΔG<0=exergonic
○ ΔG>0=endergonic
■ Only occur if energy is added
➢ Activation Energy
○ Even though exergonic reactions release energy, the reaction still needs energy to start off
with
■ Reactants must first go into transition state before turning into products
■ Activation energy is the energy needed to achieve the transition state
■ Bonds must be broken before new bonds can form
C. Enzymes
➢ Biological catalysts that speed up reactions
○ Accomplished by lowering activation energy and helping transition state form
➢ Lowers activation energy by:
○ Orienting substrate correctly
○ Straining substrate bonds
○ Providing favorable microenvironment
○ Bonding to substrate
➢ Do NOT change the energy of the starting point or the ending point of the reaction. Only lower
activation energy
➢ Enzyme Specificity
○ Each enzyme catalyzes only one kind of reactions
○ Enzymes are usually named after the molecules they target
■ Replace suffix of substrate with -ase
○ Substrates are the targeted molecules (reactant)
■ attach to the enzyme
○ Speed up reaction by lowering activation energy with an enzyme
■ Need to collide with right orientation and energy
■ reduces randomness=> more efficient
○ Enzyme substrate complex
■ Enzyme brings about transition state by helping the substrate(s) get into position
■ Accomplished through active site
■ Once the reaction has occurred, the enzyme is released from the complex and
restored to its original state
A.Bioenergetics
➢ Glucose, starch, and fat all energy-rich, but the bonds must be broken in order for the energy to
be released
➢ First Law of Thermodynamics: Energy cannot be created or destroyed. The sum of energy in
the universe is constant.
➢ Second Law of Thermodynamics: Energy transfer leads to less and less organization. The
universe tends toward entropy
➢ Types of Reactions
○ Exergonic
■ Products have less energy than the reactants
■ Energy is given off during the reaction
■ Ex. oxidation of molecules in mitochondria
○ Endergonic
■ Require an input of energy
■ Products have more energy than reactants
■ Ex. plants’ use of CO2 and water to form sugars
, B. Gibbs Free Energy
➢ ΔG=ΔH-TΔS
○ T=temperature
○ H=enthalpy (measure of energy in a thermodynamic system)
○ S=entropy
○ Change in the Gibbs free energy of a reaction determines whether the reaction in
favorable (spontaneous, negative) or unfavorable (nonspontaneous, positive)
○ Used to figure out if, without adding energy, the reactants will stay as they re or be
converted to products
➢ Spontaneous Reactions
○ Occur without a net addition of energy
○ ΔG<0=exergonic
○ ΔG>0=endergonic
■ Only occur if energy is added
➢ Activation Energy
○ Even though exergonic reactions release energy, the reaction still needs energy to start off
with
■ Reactants must first go into transition state before turning into products
■ Activation energy is the energy needed to achieve the transition state
■ Bonds must be broken before new bonds can form
C. Enzymes
➢ Biological catalysts that speed up reactions
○ Accomplished by lowering activation energy and helping transition state form
➢ Lowers activation energy by:
○ Orienting substrate correctly
○ Straining substrate bonds
○ Providing favorable microenvironment
○ Bonding to substrate
➢ Do NOT change the energy of the starting point or the ending point of the reaction. Only lower
activation energy
➢ Enzyme Specificity
○ Each enzyme catalyzes only one kind of reactions
○ Enzymes are usually named after the molecules they target
■ Replace suffix of substrate with -ase
○ Substrates are the targeted molecules (reactant)
■ attach to the enzyme
○ Speed up reaction by lowering activation energy with an enzyme
■ Need to collide with right orientation and energy
■ reduces randomness=> more efficient
○ Enzyme substrate complex
■ Enzyme brings about transition state by helping the substrate(s) get into position
■ Accomplished through active site
■ Once the reaction has occurred, the enzyme is released from the complex and
restored to its original state
