Chemical Reactions
• First Law of Thermodynamics
Enzymes and Metabolism
Chapter 4
– Matter and energy cannot be created or
destroyed, but can be converted from one form
to another
• Second Law of Thermodynamics
– As energy is transformed from one form to
another, the universe becomes increasingly
disorganized
Chemical Reactions
• Order = Free Energy
• All chemical reactions must involve a loss
in free energy
• Change in free energy during a chemical
reaction depends upon…
1. Particular energetic properties of the
reactant(s) vs. that of the product(s)
2. The concentration of the reactants(s) relative
to that of the product(s)
Reversible vs. Irreversible Reactions
• Reversible reaction
– Intrinsic energetic properties of
the reaction differ little between
converting reactants into
products and converting
products into reactants
– Relative ratio of products vs.
reactants determines net
tendency for the reaction to go
one way vs. another.
– Equilibrium – point where rate
of reaction proceeding in one
direction is equal to the rate the
reaction
[Reactant]
Reversible vs. Irreversible Reactions
[Product]
Enzymes Protein Catalysts
• Irreversible reaction
– Intrinsic energetic
properties of the
reaction greatly favor
conversion of reactants
into products
– Reactants converted to
product even if there is
very little reactant and
lots of product.
Enzymes = Protein Catalysts
• speed up the rate of chemical reactions
• are not permanently altered in the reactions
• do not change the nature of the reaction
– Change in free energy and equilibrium point
will be the same
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How do enzymes speed up
reactions?
• Lower the activation
energy for a reaction
• Have Complex 3-D structures
– amt of energy needed to get
the reaction going
• Pockets act as active sites
– bind specific substrates
– catalyze specific chemical reaction
– produce specific products
• Enzymes bind reagents
(substrates)
E + S ↔ E-S Complex ↔ E + P
– orient them so that less
energy is needed to get the
reaction going
• Names of enzymes typically indicate
function:
• Concentration of Enzyme
– lactate dehydrogenase – removes hydrogen
from lactate
– phosphatase – removes phosphate groups from
different organic compounds
• Some do not have descriptive names
– chymotrypsin - hydrolyzes peptide bonds
– ptyalin – hydrolyzes glycosidic bonds
• Inorganic ions
• Coenzymes - organic
cofactors (vitamins)
– Inhibitors – substances
that bind to enzyme and
reduce its catalytic activity
Reaction rate
– Cofactors - additional
substances needed to
catalyze reactions
Reaction rate
Factors Affecting Enzyme
Activity
– ↑ Enzyme, ↑ Rate
• Concentration of Substrate
– ↑ Substrate, ↑ Rate
– ↑ in rate limited by amount
of enzyme
Reaction Rate
Factors Affecting Enzyme
Activity
Enzyme Names
• Concentration of
Cofactors/Inhibitors
Enzymes catalyze specific
reactions
[E]
• may saturate the enzyme
Factors Affecting Enzyme
Activity
• Temperature
[cofactor]
– ↑ Temp, ↑ kinetic energy,
↑ reaction rate
– high Temp changes
structure of enzymes
• ↓’s enzyme function
[inhibitor]
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Factors Affecting Enzyme
Activity
Metabolism
• Metabolism
– 3D structure of enzymes
changes at different pH
– optimal enzyme function at
specific pH
– ↓ function at higher or
lower pH’s
Metabolism
• Metabolic Pathways
• Enzymes facilitate and control metabolism
How Does a Cell Maintain Order?
• Enzymes facilitate reactions, but
cannot drive energetically
unfavorable reactions
– Unfavorable – would gain free
energy as a result of the reaction
• To drive an energetically
unfavorable reaction, it must be
coupled to an energetically
favorable one
• Cells require a supply of free
energy (fuel) to drive biochemical
reactions
Reaction B:
Lose free energy
– long series of enzyme-catalyzed reactions
– allow high degree of control + regulation
– energetic sum of all chemical reactions
occurring in a living organism
– break down of some substances (catabolism)
– build up of other substances (anabolism)
Reaction A:
Gain free energy
• pH
Reaction A + Reaction B =
OVERALL LOSS OF FREE ENERGY!
Adenosine Triphosphate
• Energy carrier molecule
ATP → ADP + Pi + energy
• Energy used to drive
biochemical reactions
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