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Questions and Answers
What happens to free energy when a chemical reaction proceeds towards equilibrium?
What happens to free energy when a chemical reaction proceeds towards equilibrium?
Which of the following statements about enthalpy is accurate?
Which of the following statements about enthalpy is accurate?
What does the formula DG = DH - TDS represent?
What does the formula DG = DH - TDS represent?
In the context of the equilibrium constant, what happens to the standard free-energy change when a reaction reaches equilibrium?
In the context of the equilibrium constant, what happens to the standard free-energy change when a reaction reaches equilibrium?
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Which of the following best describes nucleophiles?
Which of the following best describes nucleophiles?
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What is the primary role of phosphagens in animal muscle?
What is the primary role of phosphagens in animal muscle?
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Which of the following correctly defines the relationship between equilibrium constants and standard free-energy changes?
Which of the following correctly defines the relationship between equilibrium constants and standard free-energy changes?
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Which of the following options represents a correct characterization of entropy?
Which of the following options represents a correct characterization of entropy?
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What does the first law of thermodynamics state regarding energy?
What does the first law of thermodynamics state regarding energy?
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What does the second law of thermodynamics imply about physical chemical changes?
What does the second law of thermodynamics imply about physical chemical changes?
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What equation represents the relationship between enthalpy, free energy, and entropy?
What equation represents the relationship between enthalpy, free energy, and entropy?
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Which statement is true regarding an exergonic reaction?
Which statement is true regarding an exergonic reaction?
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What happens when Keq is greater than 1?
What happens when Keq is greater than 1?
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In biological reactions, what is primarily observed when calculating ΔH?
In biological reactions, what is primarily observed when calculating ΔH?
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Which of the following best characterizes a favorable reaction?
Which of the following best characterizes a favorable reaction?
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What does ΔG measure in the context of a reaction?
What does ΔG measure in the context of a reaction?
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Which compound has a higher group-transfer potential than ATP?
Which compound has a higher group-transfer potential than ATP?
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What reaction is used to replenish ATP from phosphocreatine in muscle?
What reaction is used to replenish ATP from phosphocreatine in muscle?
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In phosphoryl-group transfer, what characterizes high-energy compounds?
In phosphoryl-group transfer, what characterizes high-energy compounds?
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What is the molecular structure that characterizes thioesters?
What is the molecular structure that characterizes thioesters?
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Which molecule is a soluble electron carrier used by dehydrogenases?
Which molecule is a soluble electron carrier used by dehydrogenases?
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What is the energy change associated with the hydrolysis of ATP?
What is the energy change associated with the hydrolysis of ATP?
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What is a consequence of niacin deficiency?
What is a consequence of niacin deficiency?
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How does ATP mainly provide energy for cellular processes?
How does ATP mainly provide energy for cellular processes?
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What is the primary outcome of the oxidative decarboxylation of luciferin in the presence of O2 and luciferase?
What is the primary outcome of the oxidative decarboxylation of luciferin in the presence of O2 and luciferase?
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In the equation for ΔG', what do the variables [C], [D], [A], and [B] represent?
In the equation for ΔG', what do the variables [C], [D], [A], and [B] represent?
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Which of the following enzymes is responsible for oxidation-reduction reactions?
Which of the following enzymes is responsible for oxidation-reduction reactions?
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What is the actual free energy change for the hydrolysis of ATP typically associated with?
What is the actual free energy change for the hydrolysis of ATP typically associated with?
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Which of the following describes the role of charge repulsion in ATP's energy release?
Which of the following describes the role of charge repulsion in ATP's energy release?
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What drives the need for energy in biological systems?
What drives the need for energy in biological systems?
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What occurs during the tautomerization of pyruvate?
What occurs during the tautomerization of pyruvate?
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Which reaction is NOT typically a type of reaction involving enzymes in living cells?
Which reaction is NOT typically a type of reaction involving enzymes in living cells?
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Study Notes
Bioenergetics
- The study of energy transformations in living cells
- A branch of biochemistry that focuses on the transformation of energy and the use of enzymes by living systems
Electron Flow Provides Energy
- Autotrophs use energy from the sun to convert inorganic compounds into organic molecules
- Heterotrophs obtain energy by consuming organic molecules produced by autotrophs
- Electron flow in these reactions is crucial for energy generation and involves oxidation-reduction reactions.
Laws of Thermodynamics
- System: the area under investigation
- Heat: the transfer of thermal energy
- Work: the force applied over a distance
First Law of Thermodynamics (Law of Conservation of Energy)
- Energy cannot be created or destroyed, only transformed from one form to another.
- Total energy leaving the system = Total energy entering the system - Stored internal energy
- In biological reactions within a cell, we are interested in enthalpy (H)
- ΔH = H (products) - H (reactants)
- Exothermic reactions release heat (ΔH negative)
- Endothermic reactions absorb heat (ΔH positive)
Second Law of Thermodynamics (Law of Thermodynamic Spontaneity)
- Physical and chemical changes result in irreversible degradation of useful energy into a random form called entropy.
- The total amount of energy in the universe decreases with time.
- Enthalpy (H): total energy of a system
- Free Energy (G): usable energy
- Entropy (S): unusable energy
- ΔG = ΔH - TΔS
- Exergonic reactions release energy (ΔG negative)
- Endergonic reactions require energy (ΔG positive)
- A highly negative ΔH and a highly positive ΔS indicate a favorable reaction.
Equilibrium Constant (Keq)
- A measure of the directionality of a reaction.
- Keq > 1: ΔG is negative, reaction proceeds spontaneously to the right (forward)
- Keq < 1: ΔG is positive, reaction proceeds spontaneously to the left (reverse)
- Reactions proceed towards equilibrium:
- Entropy increases (ΔS positive)
- Free energy decreases (ΔG negative)
- Enthalpy can be negative (system releases heat) or positive (system absorbs heat).
Types of Energy
- Useful energy: free energy that can perform work at constant pressure and temperature
- Useless energy: heat energy that can only do work at constant pressure and varying temperature; this is not possible in living organisms.
Entropy
- A measure of randomness and disorder
- Examples:
- Tea kettle: heat causes water molecules to move faster and become more disordered.
- Glucose oxidation: ordered glucose molecule is broken down into carbon dioxide and water, increasing disorder.
Nucleophiles and Electrophiles
- Nucleophiles: electron-rich groups that donate electrons
- Electrophiles: electron-deficient groups that seek electrons
- Electronegativity: a measure of an atom's ability to attract electrons
- The order of electronegativity from highest to lowest is: F > O > N > C = S > P = H
Cleavage of C-C or C-H Bonds
- These bonds are broken during chemical reactions.
Equilibrium Constant and Standard Free-Energy Change
- ΔG’reaction = ΔGo’reaction + RT ln ([C]c[D]d/[A]a[B]b)
- At equilibrium: Keq = [C]c[D]d/[A]a[B]b and ΔG’reaction = 0, therefore:
- ΔGo’reaction = -RT ln Keq
- The standard free-energy change is directly related to the equilibrium constant.
Standard Free-Energy Changes
- Standard free-energy changes are additive.
Equilibrium Constants
- Equilibrium constants are multiplicative.
Phosphagens
- Energy-rich storage molecules in animal muscle
- Examples: phosphocreatine (PC) and phosphoarginine (PA)
- Phosphoamides with higher group-transfer potentials than ATP
- Produced during times of ample ATP
- Replenish ATP when needed using creatine kinase or arginine kinase reactions.
Fireflies
- Use the energy from ATP hydrolysis to emit light
- Pyrophosphate cleavage of ATP forms luciferyl adenylate
- In the presence of oxygen and luciferase, luciferin undergoes oxidative decarboxylation to oxyluciferin and emits light.
Actual Free Energy of ATP Hydrolysis
- ΔG’ = ΔGo’ + RT ln ([C]c[D]d/[A]a[B]b)
- It is a function of reactant and product concentrations and temperature.
- The actual free energy of ATP hydrolysis is very different from the standard free energy change.
Phosphorylation Potential
- A measure of the ability of a compound to transfer a phosphoryl group.
Reaction Coupling
- Energy from an exergonic reaction is used to drive an endergonic reaction.
Common Biochemical Reactions
- Cells perform thousands of specific enzyme-catalyzed reactions.
- Reactions occur on the active sites of enzymes.
- Examples:
- Oxidation-reduction reactions (dehydrogenases)
- Group transfer reactions (kinases)
- Hydrolysis reactions (hydrolases)
- Formation of double bonds (lyases)
- Isomerization reactions (isomerases)
- Formation and breaking of C-C bonds (ligases)
Cellular Energy Requirements
- Cells require energy for:
- Maintaining their structure (biosynthesis)
- Generating motion (mechanical work)
- Active transport
- Generating heat and light.
ATP as an Energy Carrier
- ATP is the primary energy currency of cells.
- Energy from the oxidation of metabolic fuels is largely recovered in the form of ATP.
- Highly-energetic phosphoanhydride bonds provide energy.
- The high energy of ATP is attributed to:
- Charge repulsion between the phosphate groups
- Resonance stabilization of the products of hydrolysis
- High entropy of the products compared to ATP.
Hydrolysis of Phosphoenolpyruvate (PEP)
- Catalyzed by pyruvate kinase
- The reaction is followed by spontaneous tautomerization of the product pyruvate, which contributes to the large negative free energy change.
- PEP cannot tautomerize, so the products of hydrolysis are more stable than the reactants.
Phosphoryl-Group Transfer Potential
- The ability of a compound to transfer its phosphoryl group.
- Energy-rich compounds have group transfer potentials equal to or greater than that of ATP.
- Low-energy compounds have group transfer potentials less than that of ATP.
Thioesters
- Thioesters contain a sulfur atom in the position occupied by an oxygen atom in oxygen esters.
- The hydrolysis of acetyl-CoA, a thioester, provides a large negative free energy change.
NADH and NADPH
- Soluble electron carriers
- Nicotinamide derived from vitamin niacin (B3).
- NADH absorbs at 340 nm.
- Most dehydrogenases that utilize NAD or NADP bind the cofactor to a conserved protein domain.
Effects of Niacin Deficiency
- Pellagra: characterized by dermatitis, diarrhea, and dementia.
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Description
Explore the principles of bioenergetics and thermodynamics in this quiz. Understand energy transformations, the role of electron flow in living organisms, and the laws governing energy conservation. Test your knowledge on how energy is utilized by autotrophs and heterotrophs.
