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Biology Notes on Metabolism.
Citation preview
10/13/2014
1
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:
Off On