ENZYMES
Energy and Enzymes
Life requires energy.
Almost all energy for life is derived from the
sun.
A “factoid” The sun’s energy that strikes Earth each day
is equivalent to one million Hiroshima-sized
atomic bombs.
Photosynthesis harnesses about 1% of that
energy – 10,000 “atomic bomb equivalents”
per day.
ENZYMES
Chemistry and Life
One unromantic yet productive way of
viewing life is to see it as a set of
coordinated chemical reactions.
This leads to an obvious question – What
determines what chemical reactions are
possible?
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Chemical Reactions
Whether a chemical reaction will or won’t occur under particular
conditions is determined by the laws of thermodynamics.
Keeping it simple If the overall amount of order is decreased by a reaction, the
reaction is wanted.
If the overall amount of order is increased by a reaction, the
reaction is not wanted.
ENZYMESThe Direction of Spontaneous Reactions (and what
it takes to go the other way)
Going this way is possible, but it requires the input of energy.
ENZYMES
Life Requires Lots of Unfavorable Reactions – How Is This Possible?
By coupling
favorable, energyreleasing reactions to
unfavorable, energyrequiring reactions.
favorable
reactions
unfavorable
reactions
ENZYMES
The “Nature of Life” – Coupling Favorable, Energy Yielding Reactions to Unfavorable, Energy-Requiring
Reactions
ENZYMES
Even When Cells Build Complex Molecules and Structures, the Second
Law of Thermodynamics (Entropy or the “kids bedroom principle”)
Isn’t Violated
ENZYMES
ATP - Life’s
Energy
Currency
Energy is released
when ATP is
hydrolyzed (broken
down) to ADP.
ATP is restored
from ADP and an
input of energy.
ATP’s energy is
used to drive
endergonic
(energy-requiring)
reactions.
ENZYMES
The Way ATP Often
Works
ENZYMES
Enzymes Speed Biochemical Reactions
Enzymes are biological catalysts – substances that speed a reaction
without being altered in the reaction.
Most enzymes are proteins, some are RNA.
Enzymes are essential for life.
Model of the surface of an enzyme.
ENZYMES
Enzymes
Lower a
Reaction’s
Activation
Energy
ENZYMES
Enzyme Action
ENZYMES
The Fit Between
Enzyme and
Substrate is Critical
and Precise
Hexokinase,
an enzyme
(blue),
binding its
substrate,
glucose
(yellow).
ENZYMES
Many
Enzymes
Work by
Altering the
Shape of
Their
Substrates
The active site
of an enzyme is
where substrate
is bound.
ENZYMES
Metabolic Pathways
The synthesis of biological molecules often requires many enzymecatalyzed steps.
The entire set of steps is a metabolic pathway.
ENZYMES
Enzyme Activity is Often
Regulated
Feedback inhibition - a
common form of enzyme
regulation in which the
product inhibits the enzyme .
ENZYMES
Enzymes allow chemical reactions to occur under tightly
controlled conditions.
• Enzymes are catalysts in living things.
– Enzymes are needed for almost all processes.
– Most enzymes are proteins.
ENZYMES
• Proteins
– Enzymes as Biological
Catalysts
- Increase reaction rates
by over 1,000,000-fold
- Two fundamental
properties
· Increase the reaction
rate with no alteration
of the enzyme
· Increase the reaction
rate without altering
the equilibrium
- Reduce the activation
energy
ENZYMES
• Disruptions in homeostasis can prevent enzymes from
functioning.
– Enzymes function best in a small range of conditions.
– Changes in temperature and pH can break hydrogen
bonds.
– An enzyme’s function depends on its structure.
ENZYMES
• An enzyme’s structure allows only certain reactants to
bind to the enzyme.
– substrates
– active site
substrates
(reactants)
enzyme
Substrates bind to an
enzyme at certain places
called active sites.
ENZYMES
• Proteins
– Enzymes as Biological
Catalysts
- Two popular models
provide an aid to
understanding the
mechanisms of enzyme
action:
· Lock-and-key
· Induced fit
ENZYMES
• The lock-and-key model helps illustrate how enzymes
function.
– substrates brought together
– bonds in substrates weakened
Substrates bind to an
enzyme at certain
places called active
sites.
The enzyme brings
substrates together
and weakens their
bonds.
The catalyzed reaction forms
a product that is released
from the enzyme.