enzymes&energy

Chapter 4

Enzymes and Energy

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Enzymes

Biological catalysts. Increase rate of chemical

reactions. Most enzymes are proteins

with diverse structure.


Biological Catalyst Chemical that:

Increases the rate of a reaction. Is not changed at the end of the

reaction. Does not change the nature of the

reaction or final result. Lowers the activation energy required.

Activation energy: Amount of energy required for a

reaction to proceed.


Activation Energy


Mechanism of Enzyme Action

Each type of enzyme has has a characteristic 3-dimensional shape (conformation).

Has ridges, grooves, pockets lined with specific amino acids.

Pockets active in catalyzing a reaction are called the active sites of the enzyme.


Mechanism of Enzyme Action

Lock-and-key model of enzyme activity:

Reactant molecules (substrates) have specific shapes to fit into the active sites. Substrate fits into active sites in

enzyme. Enzyme-substrate complex dissociates. Products of reaction formed and free

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Naming of Enzymes

Enzyme name ends with ase. Classes of enzymes named

according to activity. Enzymes that have the same

activity in different organs may make different models called isoenzymes.


Control of Enzyme Activity

Rate of enzyme-catalyzed reactions measured by the rate substrates are converted to products.


Control of Enzyme Activity

Factors influencing rate: Temperature pH [cofactors and coenzyme] [enzyme and substrate] Stimulatory and inhibitory

effects of products


Effect of Temperature

Increase in temperature increases rate of reaction.

At body temperature, plateaus.

Denature at high temperatures.


pH

Each enzyme exhibits peak activity at narrow pH range (pH optimum).

Optimum pH reflects the pH of the body fluid in which the enzyme is found.


Cofactors and Coenzymes

Cofactor: Attachment of cofactor causes a

conformational change in enzyme. Participate in temporary bonds

between enzyme and substrate. Coenzymes:

Cofactors that are organic molecules derived from niacin, riboflavin and other H20 soluble vitamins.


Substrate Concentration

Rate of product formation will increase as the [substrate].

Plateau of maximum velocity occurs when enzyme is saturated.


Reversible Reactions

H20 + C02 H2C03

Direction of reversible reaction depends on the concentration of molecules to the left and right of the arrows.

ca


Sequence of enzymatic reactions that begins with initial substrate, progresses through intermediates and end with a final product.


An intermediate can serve as substrate for 2 different enzymes, producing 2 different products.


Negative feedback inhibition. One of the finalproducts inhibits the activity of the branch enzyme.Prevents final product accumulation.


Inborn Errors of Metabolism

Inherited defect in a gene. Quantity of intermediates

formed prior to the defect increases.

Final product decreases, producing a deficiency.


Cannot produce tyrosine, PKU results.Cannot produce melanin, albinism results.


Bioenergetics

Flow of energy in living systems. 1st law of thermodynamics:

Energy can be transformed, but it cannot be created or destroyed.

2nd law of thermodynamics: Energy transformations increase

entropy. Free energy can be used to do work.


Endergonic Reactions

Chemical reactions that require an input of energy.

Products must contain more free energy than reactants.


Exergonic Reactions

Convert molecules with more free energy to molecules with less.

Release energy in the form of heat. Heat is measured in calories. Calorie:

Amount of heat to raise the temperature of one cubic centimeter of H20 one degree Celsius.


Coupled Reactions: ATP

Cells cannot use heat for energy.

Require energy released in exergonic reactions (ATP) to be directly transferred to chemical-bond energy in the products of endergonic reactions.


Universal energy carrier of the cell.www.freelivedoctor.com

Oxidation-Reduction

Reduced: Molecule/atom gains electrons.

Reducing agent: Molecule/atom that donates electrons.

Oxidized: Molecule/atom loses electrons.

Oxidizing agent: Molecule/atom that accepts electrons.

May involve the transfer of H+ rather than free electrons.


Reduced form.


Oxidized form.


enzymes&energy

Documents

free enzyme

free energy

coenzyme enzyme

type of enzyme

branch enzyme

activation energy

enzymesubstrate complex

naming of enzymes enzyme