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Enzymes

Enzymes are biological catalysts

Proteins

Catalyst Lower activation energy Increases the rate of the reaction Affects nothing other than the reaction rate Does NOT affect the free energy of the reaction

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Bonds break, new bonds are formed releasing energyEnergy that is

absorbed in order to reach transition state

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Enzyme Activity is affected by…

Concentration of substrate

Concentration of enzyme

If enzyme is saturated, then rate is determined by enzyme’s rate for converting substrate to product

Cofactors / Coenzymes presence

Presence of Inhibitors

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Enzymatic Regulation

Enzymes = proteins Proteins have 3D

structure Affected by pH and

Temperature Structure & function

relationship

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Enzyme Assistants

Cofactors Nonprotein molecules that enzymes require

for catalytic activity Typically, inorganic

Such as zinc, iron, and copper

Coenzymes Organic cofactor (what does organic mean?) Vitamins

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Competitive Inhibition

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Questions

1. How does competitive inhibition differ from noncompetitive inhibition?

2. How does a cofactor differ from a coenzyme?

3. Name 3 things that affect enzyme activity?

4. What does an enzyme do?

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Pathway Regulation

2 main ways to regulate metabolic pathways: 1. Switching on/off genes 2. Regulating enzyme activity

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Allosteric Regulation

Allosteric – specific binding site NOT the active site!! Can be inhibition or activation

Allosteric molecule binds to a site other than the active site

Allosteric molecule binding enzyme shape change Change in enzyme shape active site shape change Structural change = Functional change

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Allosteric Regulation

Enzyme units oscillate between two conformational sites One is catalytically active, the other is

inactive

Regulatory site Called allosteric site Activator or inhibitor binds and stabilizes the

conformational form Usually an activator or inhibitor affects all

active sites

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Cooperativity

When a substrate molecule causes an induced fit in one active site triggers the same change in all subunits of the enzyme

Amplifies the response of enzymes to substrates Primes the enzyme to accept more substrate

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Feedback Inhibition

A metabolic pathway is switched off by the inhibitory binding of its end product to an enzyme that acts early in the pathway

An example of allosteric inhibition

Increases efficiency of a pathway Pathway is turned off when product

accumulates

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Final Questions

1. What happens to an enzyme in a chm rxn?

2. How does allosteric inhibition differ from noncompetitive inhibition?

3. What is the allosteric site?

4. How does cooperativity differ from allosteric activation?

5. What is the most effective method of pathway regulation?