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Life Sciences 2Lecture 4

Energy, Enzymes, and Metabolism

Energy, Enzymes, and Metabolism

In living organisms, thousands of enzyme catalyzed reactions occur

Catalysis occur due to the 3-D shape of theCatalysis occur due to the 3 D shape of the proteins involved

Metabolism is the combination of all of these reactions

Enzymes and Energetic

Energy and the Laws of Thermodynamics Chemical Reactions and Equilibrium Reaction Rates and the Energy Barrier Reaction Rates and the Energy Barrier Enzymes

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Energy and the Laws of Thermodynamics

Bioenergetics is the flow of energy in biochemical systems

Energy is defined as the capacity to do workEnergy is defined as the capacity to do work Forms of Energy: Heat, light, electrical, and

chemical

Energy and the Laws of Thermodynamics

Energy can be considered as one of two basic types:

Kinetic EnergyKinetic Energy Potential Energy

Energy and the Laws of Thermodynamics

Kinetic energy is the energy associated with motion

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Energy and the Laws of Thermodynamics

Potential energy is the energy of state gyor position

Energy and the Laws of Thermodynamics

Energy before and after transformation is equalequal

After energy transformation The amount of energy available to do work is less.

With repeated energy transformations usable energy decreases and unusable

Energy and the Laws of Thermodynamics

energy increases.

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With repeated energy transformations usable energy decreases and unusable

Energy and the Laws of Thermodynamics

energy increases. (Entropy) This occurs in a closed system.

Energy and the Laws of Thermodynamics

In a closed system, no energy or matters enters or leave

First law: within closed systems energy is neither destroyed nor created

No change in quantity

Energy and the Laws of Thermodynamics

No change in quantity

Not all energy can be used. The usable portion of energy is decreasing

Quality of energy changes

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Energy and the Laws of Thermodynamics

Open systems can be part of larger closed system

An open system can increase its order andAn open system can increase its order and complexity using free energy from the closed sytem

Where does living matter gets its energy from?

Definitions:

Usable energy

Unusable energy

G = H- TS

Enthalpy (H): Total Energy of the System

Entropy (S): Amount of disorder in the System

Free Energy (G): Amount of Useable Energy

Temperature(T): Amplifies entropy of the system

Applying the second law of thermodynamics:

Reactions spontaneously go from high levels of useful energy (G) to low level of useful energy

G tends to decrease S tends to increaseG tends to decrease. S tends to increase.H is constant, but the quality changes

All things tend towards disorder

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Diffusion

Less Entropy (S)Order

More EntropyDisorder

Chemical Reactions Release or Take Up Energy

Exergonic Reaction: release of energy

Endergonic Reaction: uptake of energy

Starch

Glucose

Chemical Reactions Release or Take Up Energy

Starch

Glucose

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Glucose

CO2

Chemical Reactions Release or Take Up Energy

Glucose

CO2

Exergonic Reaction:

Energy is released as the reaction proceeds to form products. G is negative

Ball has potential energy. When releases it rolls down the hill spontaneously. Its Energy decreases.

Exergonic Reaction:

Spontaneous reaction, that goes to completion over time without any energy input. It releases energy by breaking bonds.

G product < G reactant ==> G is negativeG product < G reactant ==> G is negativeGlucose +O2 -> 6 CO2 + H2O + energy

The energy produced can be used to form ATP, but some is lost as heat.Entropy increases, usually in the form of heat or light

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Endergonic Reaction:A reaction that requires input of free energy to proceed. It is NOT spontaneous.G reactant < G product ==> G is positiveADP + Pi -> ATPGlucose + Glocuse + -> Glycogen

Exergonic Reaction:

Chemical Equilibrium and Free Energy are related

All chemical reactions are reversible

A-->B (forward reaction) ( )A

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Gl 1 Ph h < > Gl 6 Ph hGlucose 1-Phospahe Glucose 6 Phospahe

When the reaction reaches equilibrium there will be 0.001 M G1-P and 0.019 M G6-P

Keq = 0.19/0.01= 19Keq= [Products]/[Reactants]

Equilibrium Constant:

Keq is the ratio of products and reactants at equilibrium.

High value means that reaction goes to g gcompletion

Rate of a reaction:

Is equal to the product of the rate constant and the concentration of the reactant

A->B

Rate of reaction is Kf x [A]

Each molecule of A is converted to B at rate Kf. This rate is specific to the reaction

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Equilibrium in a reaction exists when the rate of the forward reaction equals the rate of the reverse reaction

Kf A->B = Kr B->A

G and Equilibrium:Keq >1 more products than reactants. This is an exergonic reaction with a negative G Keq

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Reaction Rates and the Energy Barrier

Thermodynamics: relates to G. This determines the direction but not the speed of the reaction

Kinetics: describes the rate of the reaction

Glucose +O2 -> 6 CO2 + H2O + energyG = -686 kcal/mole

Sugar + Oxygen = Sugar + Oxygen

No reaction will happen.

Sugar + Oxygen = Heat + CO2

+ Spark (Activation Energy Ea)

Activation Energy

Even though some chemical reactions have a negative G, they can not proceed without an aid

G determines the direction of a reaction but not its rate

To initiate a reaction, Ea is needed

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Activation Energy

Reaction Rates are affected by motion of molecules to go from reactant to product

Activation Energy is the amount of energyActivation Energy is the amount of energy required to push the reactant to proceed and overcome the energy barrier

Rate constant (Kf or Kr) is related to the activation energy barrier

The rate of the reaction depends on the activation energy. How can we increase the reaction rate?

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Add heat: This will increase the motion of the motion of the molecules.

Increase the concentration of the reactants.

Lower the activation energy: Biological systems use protein catalysts (enzymes) to lower activation energy and speed the reaction rate (this does not change G).

What is a catalyst?

When oxygen and sulfur dioxide are mixed in the presence of a filament of platinum, they from sulfurous acid. This combination takes

l l if th l ti i tplace only if the platinum is present; nevertheless the newly formed acid contains no trace of platinum and the platinum itself is unaffected and unchanged

Enzymes:

Cells can control the speed of reactions by using protein catalysts called enzymes.

E h th d f bi h i lEnzymes enhance the speed of biochemical reactions

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Substrate fits precisely into the active site

Enzymes is a protein with a binding site capable of binding one or substrate molecules

Nonsubstrate does not

Enzymes:

The enzymes are not changed

They alter the rate of the reaction

They do not change GThey lower the activation energy of the reaction

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Enzymes have different ways of causing their substrate to enter the transition state

Specificity of the enzyme for the substrate is determined by the proteins tertiary structure

Hexokinase

An enzyme binds to a substrate at the active site to form enzyme-substrate complex

The fit of a substrate to the enzyme is highly specific based on shape, H-bonds, hydrophobic interactions

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Which substrate-enzyme binding mechanism is this?

Enzymes catalyze reactions at very specific conditions:

Enzymes catalyze reactions at very specific conditions:

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Reaction rate levels off when enzymes are saturated

Have you seen this before?

is reached when all carriers are saturated

How are enzymes regulated?

Cofactors: Copper or zinc are essential for enzyme functioning

Coenzymes: organic molecules required for the action of certain enzymes (NAD, FAD)

Prosthetic groups: Permanently bound to enzymes (heme groups)

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How are enzymes regulated?

Inhibitors

Feedbackloops

Allosteric regulation

Enzymes can be inhibitedReversible inhibition

Enzymes can be inhibitedReversible inhibition

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Enzymes can be inhibitedReversible inhibition

Enzymes can be inhibitedReversible inhibition

Enzymes can be inhibited by feedback control:A-->B-->C-->DD the final product inhibits the enzyme that catalyzes the reaction A-->B

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Enzymes can be inhibited byAllosteric Control:

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