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Chapter 8 - Coggle Diagram
Chapter 8
Enzymes speed up metabolic
reactions
The Activation Energy Barrier
A molecule must be contorted into a highly
unstable state before bonds can break to start the
reaction
activation energy (EA) - initial energy needed to break the bonds of the reactants
The activation energy provides a barrier that
determines the rate of spontaneous reactions
Catalyst - a chemical agent that speeds up a
reaction without being consumed by the reaction
Enzyme - a macromolecule (typically protein)
that acts as a catalyst to speed up a specific
reaction
How Enzymes Speed Up Reactions
An enzyme cannot change ΔG; it only speeds up a
reaction that would eventually occur anyway
organisms carry out catalysis, the process
by which a catalyst selectively speeds up a reaction
without itself being consumed
Substrate Specificity of Enzymes
active site is the region on the enzyme, often
a pocket or groove, that binds to the substrate
Enzyme-substrate complex - enzyme binds to its substrate
Substrate - reactant that an enzyme acts on
induced fit results from interactions between
chemical groups on the substrate and the active
site
Catalysis in the Enzyme’s Active Site
The conversion of substrate to product happens
rapidly, and product is released from the active site
Cofactors
coenzymes - Organic cofactors
Cofactors - nonprotein helpers that bind to the
enzyme permanently, or reversibly with the
substrate
Enzyme Inhibitors
Many inhibitors bind to the enzyme by weak
interactions, resulting in reversible inhibition
Competitive inhibitors closely resemble the
substrate, and can bind to the enzyme’s active site
Noncompetitive inhibitors bind to another part of
the enzyme, away from the active site
The Evolution of Enzymes
Changes in genes (mutations) lead to changes
in the amino acid composition of the enzyme
Enzymes are proteins encoded by genes
Introduction to Metabolism
Catabolic pathways - release energy by breaking
down complex molecules into simpler compounds
Anabolic pathways - consume energy to build
complex molecules from simpler ones
An organism's metabolism
metabolic pathway - specific molecule is
altered in a series of steps to produce a product
Metabolism - the totality of an organism’s
chemical reactions
EX: Living things use energy released from the downhill
reactions of catabolic pathways to power the uphill
reactions of anabolic pathways
EX: Catabolic = downhill / Anabolic = uphill
Forms of Energy
Energy - the capacity to cause change, can be used
to do work move matter against opposing forces,
such as gravity and friction
Kinetic energy - energy associated with motion
Thermal energy - transfer from one object to
another is called heat
Potential energy - energy that matter possesses
because of its location or structure
Chemical energy - potential energy available for
release in a chemical reaction
The Laws of Energy Transformation
Thermodynamics - the study of energy
transformations in a collection of matter
First Law -Energy can be transferred and transformed, but it
cannot be created or destroyed
Second Law - Every energy transfer or transformation increases
the entropy of the universe and measures of molecular disorder, or randomness
Spontaneous processes - occur without energy
input; they can happen quickly or slowly
The free-energy change of a
reaction
Free Energy, Stability, and Equilibrium
Equilibrium, the point at which forward and reverse
reactions occur at the same rate Systems never spontaneously move away from equilibrium
ΔG represents the difference between free energy
of the final state and free energy of the initial state
Free energy can be thought of as a measure of a
systems stability; unstable systems (higher G) tend
to become more stable (lower G)
Exergonic and Endergonic Reactions in
Metabolism
Exergonic reaction (“energy outward”) - proceeds
with a net release of free energy to the surroundings
Endergonic reaction (“energy inward”) - absorbs
free energy from the surroundings
exergonic reactions the products store less free
energy than the reactants, because ΔG is negative, exergonic reactions occur spontaneously
endergonic reactions, the products store more
free energy than the reactants Because ΔG is positive, endergonic reactions are nonspontaneous
Free-Energy Change, G
The ΔG for a process can be used to determine
whether it is spontaneous or not
Gibbs free energy, G, can be simplified and
referred to as free energy
Free energy - the portion of a system’s energy
that can do work when temperature and pressure are uniform throughout a system of living cells
ΔG is negative for all spontaneous processes
ΔG is zero or positive for nonspontaneous processes
Equilibrium and Metabolism
cells allow
materials to flow in and out
the flow of materials prevents metabolic
equilibrium, enabling cells to continue doing work
he chemical reactions of metabolism are
reversible, but never reach equilibrium in a living cell
ATP powers cellular work
The Structure and Hydrolysis of ATP
ATP (adenosine triphosphate) is composed of
ribose (a sugar), adenine (a nitrogenous base), and
three phosphate groups
ATP functions as
one of the nucleoside triphosphates used to make RNA
How ATP Provides Energy That Performs Work
Cellular work (mechanical, transport, and chemical)
is powered by ATP hydrolysis
ATP hydrolysis causes a change in protein shape
and binding ability
phosphorylated intermediate, is more reactive (less stable, with
more free energy) that the original molecule
cell does three main kinds of work
Transport work—pumping substances across
membranes against the direction of spontaneous
movement
Mechanical work—such as beating cilia or
contracting muscle cells
Chemical work—pushing endergonic reactions
energy coupling - Cells manage energy resources to do work and use of an exergonic process to drive an endergonic one through ATP
The Regeneration of ATP
Free energy needed to phosphorylate ADP comes
from exergonic breakdown reactions (catabolism)
ATP is regenerated by addition of a phosphate
group to adenosine diphosphate (ADP)
Regulation of enzyme activity
Allosteric Activation and Inhibition
Cooperativity - substrate binding to one active
site triggers a shape change in the enzyme that
stabilizes the active form for all other sites
allosterically regulated enzymes are made
from polypeptide subunits, each with its own active site
Feedback Inhibition
feedback inhibition, the end product of a
metabolic pathway shuts down the pathway
prevents a cell from wasting
chemical resources by synthesizing more product than is needed
Allosteric Regulation of Enzymes
Allosteric regulation occurs when a regulatory
molecule bindsto a protein at one site and affects
the protein’s function at another site
May either inhibit or stimulate enzyme activity
Localization of Enzymes Within the Cell
Compartmentalization of the cell helps to bring
order to metabolic pathways
Some enzymes have fixed locations and act as
structural components of particular membranes