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

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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.

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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.

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Enzymes Lower a Reaction’s Activation Energy

ENZYMES Enzyme Action

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The Fit Between Enzyme and Substrate is Critical and Precise

Hexokinase, an enzyme (blue), binding its substrate, glucose (yellow).

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The active site of an enzyme is where substrate is bound.

Many Enzymes Work by Altering the Shape of Their Substrates

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The synthesis of biological molecules often requires many enzyme-catalyzed steps.

The entire set of steps is a metabolic pathway.

Metabolic Pathways

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Enzyme Activity is Often Regulated

Feedback inhibition - a common form of enzyme regulation in which the product inhibits the enzyme .

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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.

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• 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

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• 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.

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• 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.

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• Proteins– Enzymes as Biological

Catalysts- Two popular models

provide an aid to understanding the mechanisms of enzyme action:

· Lock-and-key· Induced fit

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• 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.