Introduction to Bioenergetics

Introduction to Bioenergetics

• Bioenergetics is the flow of energy through living organisms
• Energy is required to overcome the second law of thermodynamics.
• The second law states that in a natural thermodynamic process, the sum of the entropies of the interacting thermodynamic systems increases.
• This means that if energy is not used to maintain an ordered state, the system will become more disorganized (increase in entropy).
• Organisms need energy, and cells need energy
• The form and structure of an organism is influenced by how it acquires energy.
• Plants have large surface areas for photosynthesis
• Carnivores tend to be fast-moving
• Herbivores have large stomachs for fermenting grass

What is Bioenergetics? (continued)

• Bioenergetics is the flow of energy through living organisms.
• Organisms need energy to maintain an ordered state, counteract the increase in disorder (entropy) within the universe.
• A simple example: an ice cube (ordered structure) turns into a puddle of water (less ordered).

Complex Systems

• Living systems become more ordered
• Living systems use energy to overcome the tendency to increase local entropy
• Entropy within the surrounding universe increases

Bioenergetics is Metabolism

• For organisms to grow, cells need energy, precursor metabolites, and reducing power (electrons).
• Metabolism is a series of enzymatic reactions
• Metabolism uses food to produce energy, building blocks, run cellular processes, and create larger molecules.

Catabolism and Anabolism

• Catabolism: breaking down foodstuff to release energy, simple compounds, reducing power.
• Anabolism: using energy and simple compounds from catabolism, reducing power to create complex molecules

Metabolism = Catabolism + Anabolism

• Catabolism: degradative, oxidative, energy-yielding, uses various starting materials, has well-defined products, uses NAD+ or NADP+.
• Anabolism: synthetic, reductive, energy-requiring, has well-defined starting materials, has a variety of products, uses NADPH.

Oxidation and Reduction (OILRIG)

• Oxidation is the loss of electrons
• Reduction is the gain of electrons

Thermodynamics = Energy Changes

• Internal Energy (E): total energy of the system
• Enthalpy (H): heat content
• Entropy (S): degree of disorder
• Gibbs Free Energy (G): energy available to do work
• Temperature (T): temperature of the system in Kelvin

Thermodynamics Refresher

• ΔG is a measure of energy potentially available to do work.
• ΔG = ΔH - TΔS

Free Energy

• Free energy is related to the total chemical energy of a system, and thus to its stability.
• High free energy indicates a potentially unstable system
• A system tends to a lower energy state (spontaneous change)
• A ΔG of 0 indicates a system at equilibrium

Exergonic and Endergonic Reactions

• Exergonic reactions release energy, ΔG is negative.
• Endergonic reactions require energy, ΔG is positive.

The ATP Cycle

• ATP couples exergonic and endergonic reactions.
• ATP releases energy when hydrolyzed, forming ADP and Pi, driving other reactions.

Standard State Conventions for Biochemists

• Standard Gibbs Free energy change (ΔG°) is calculated at pH 7.
• ΔG°' = -RTlnK_eq (where R is the gas constant, T is temperature in Kelvin, and K_eq is the equilibrium constant.)

Biochemistry, Metabolism, and Thermodynamics

• Living organisms maintain a steady state, not an equilibrium.
• Enzymes speed up reactions by lowering activation energy.

Molecules of Interest

• ATP: the key energy currency for cells (adenosine triphosphate).

Adenosine Triphosphate (ATP)

• Acts as an energy carrier
• When hydrolyzed, energy is released
• ΔG°′ = -30.5 kJ/mol

Why is energy released upon hydrolysis of ATP?

• Electrostatic repulsion: 4 adjacent negative charges in ATP repel each other
• Increase in entropy: hydrolysis releases more particles
• Resonance stabilization of products

Acyl Phosphates

• High energy release when bond hydrolysed
• Higher energy level than ATP.
• Used in substrate level phosphorylation
• Kinase enzymes pass phosphate groups directly to ADP, making ATP

Enol Phosphates

• High energy release when bond hydrolyzed
• Used in substrate level phosphorylation
• An example from glycolysis
• Enzyme: pyruvate kinase

Thioesters

• Thiols contain sulfur
• Thioesters are from the reaction between carboxylic acids and thiol groups
• High energy release when bond hydrolyzed.
• May have been an earlier high-energy compound before ATP

Coenzyme A (CoA)

• Common intermediate in many metabolic reactions
• CoA participates in the breakdown of carbohydrates and fats, converting pyruvate to acetyl-CoA and CO₂

Nicotinamide Adenine Dinucleotides (NAD+ and NADP+)

• NAD+ and NADP+ are oxidised forms
• They accept two electrons and a proton on the nicotinamide ring, becoming NADH (or NADPH) in a reducing reaction
• Act as electron carriers
• In the electron transport chain (ETC), NADH is oxidised, releasing energy used to produce ATP

Flavin Adenine Dinucleotide (FAD)

• FAD has similar functions to NAD+, acting as an electron carrier
• Has a flavin ring not a nicotinamide ring
• It can be reduced to its reduced form FADH₂ binding two electrons and two protons. Oxidization of FADH₂ in ETC releases energy for ATP synthesis

In Summary

• Cells need energy, precursor metabolites, and reducing power (electrons)
• Catabolism and anabolism are linked
• Gibbs free energy tells us how much useful work can be obtained.

Abbreviations

• A list of abbreviations for terms and molecules used in the lecture is provided

MCQ Quizzes

• Quizzes on the topics covered in the lecture will help aid understanding concepts.

This quiz explores the concept of bioenergetics, the flow of energy through living organisms, and its significance in maintaining order against entropy. Learn about how different organisms acquire energy and the structural adaptations that arise from their energy needs. Test your knowledge on these essential biological principles.