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ENZYMES Chemical Reactions Whether a chemical reaction will or won’t occur under particular conditions is determined by the laws of thermodynamics. If the overall amount of order is decreased by a reaction, the reaction is wanted. Keeping it simple - If the overall amount of order is increased by a reaction, the reaction is not wanted.
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ENZYMES Energy and Enzymes
Almost all energy for life is derived from the sun.
Life requires energy.
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?
ENZYMES Chemical Reactions
Whether a chemical reaction will or won’t occur under particular conditions is determined by the laws of thermodynamics.
If the overall amount of order is decreased by a reaction, the reaction is wanted.
Keeping it simple -
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.
ENZYMESLife Requires Lots of Unfavorable Reactions – How Is This Possible?
By coupling favorable, energy-releasing reactions to unfavorable, energy-requiring 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
ENZYMESATP - Life’s Energy CurrencyEnergy 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
ENZYMESEnzymes 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
The active site of an enzyme is where substrate is bound.
Many Enzymes Work by Altering the Shape of Their Substrates
ENZYMES
The synthesis of biological molecules often requires many enzyme-catalyzed steps.
The entire set of steps is a metabolic pathway.
Metabolic Pathways
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 anenzyme 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 anenzyme at certain places called active sites.
The enzyme bringssubstrates together and weakens their bonds.
The catalyzed reaction formsa product that is releasedfrom the enzyme.