Bioenergetics and Thermodynamics

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Questions and Answers

What happens to free energy when a chemical reaction proceeds towards equilibrium?

Free energy increases

Free energy remains constant

Free energy decreases (correct)

Free energy fluctuates unpredictably

Which of the following statements about enthalpy is accurate?

Enthalpy measures the internal energy and the work done due to volume changes (correct)

Enthalpy only applies to gases

Enthalpy is unrelated to heat content

Enthalpy is always negative

What does the formula DG = DH - TDS represent?

The change in total energy

The standard free energy at equilibrium

The relationship between free energy, enthalpy, and entropy (correct)

The rate of a chemical reaction

In the context of the equilibrium constant, what happens to the standard free-energy change when a reaction reaches equilibrium?

It is equal to zero Signup and view all the answers

Which of the following best describes nucleophiles?

Functional groups rich in electrons capable of donating them Signup and view all the answers

What is the primary role of phosphagens in animal muscle?

To serve as energy-rich storage molecules Signup and view all the answers

Which of the following correctly defines the relationship between equilibrium constants and standard free-energy changes?

Equilibrium constants relate to free energy inversely Signup and view all the answers

Which of the following options represents a correct characterization of entropy?

It relates to the degree of randomness and disorder Signup and view all the answers

What does the first law of thermodynamics state regarding energy?

Energy can neither be created nor destroyed, only transformed. Signup and view all the answers

What does the second law of thermodynamics imply about physical chemical changes?

They undergo irreversible degradation into a random form known as entropy. Signup and view all the answers

What equation represents the relationship between enthalpy, free energy, and entropy?

ΔG = ΔH – TΔS Signup and view all the answers

Which statement is true regarding an exergonic reaction?

It occurs spontaneously and releases free energy. Signup and view all the answers

What happens when Keq is greater than 1?

ΔG has a negative value and the reaction proceeds spontaneously to the right. Signup and view all the answers

In biological reactions, what is primarily observed when calculating ΔH?

The difference in energy states between products and reactants. Signup and view all the answers

Which of the following best characterizes a favorable reaction?

It has a highly negative ΔH and highly positive ΔS. Signup and view all the answers

What does ΔG measure in the context of a reaction?

How far from equilibrium a reaction lies and the energy released to reach it. Signup and view all the answers

Which compound has a higher group-transfer potential than ATP?

Phosphocreatine (PC) Signup and view all the answers

What reaction is used to replenish ATP from phosphocreatine in muscle?

Creatine and arginine kinase reaction Signup and view all the answers

In phosphoryl-group transfer, what characterizes high-energy compounds?

They have group transfer potentials equal to or greater than ATP. Signup and view all the answers

What is the molecular structure that characterizes thioesters?

They have a sulfur atom in place of an oxygen atom. Signup and view all the answers

Which molecule is a soluble electron carrier used by dehydrogenases?

NADH Signup and view all the answers

What is the energy change associated with the hydrolysis of ATP?

It produces a large free energy change. Signup and view all the answers

What is a consequence of niacin deficiency?

Disruption in electron transport chain functioning Signup and view all the answers

How does ATP mainly provide energy for cellular processes?

Via the transfer of its phosphoryl group Signup and view all the answers

What is the primary outcome of the oxidative decarboxylation of luciferin in the presence of O2 and luciferase?

Conversion to oxyluciferin and light emission Signup and view all the answers

In the equation for ΔG', what do the variables [C], [D], [A], and [B] represent?

Concentrations of products and reactants Signup and view all the answers

Which of the following enzymes is responsible for oxidation-reduction reactions?

Dehydrogenases Signup and view all the answers

What is the actual free energy change for the hydrolysis of ATP typically associated with?

Negative free energy change Signup and view all the answers

Which of the following describes the role of charge repulsion in ATP's energy release?

It enhances the hydrolysis reaction. Signup and view all the answers

What drives the need for energy in biological systems?

Generating motion and maintaining gradients Signup and view all the answers

What occurs during the tautomerization of pyruvate?

It stabilizes the product of hydrolysis Signup and view all the answers

Which reaction is NOT typically a type of reaction involving enzymes in living cells?

Phase transition Signup and view all the answers

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.