Basic Principles of Energy Conservation | Zoology Optional Notes for UPSC PDF Download

Microbial Energy Ledger: The Dance of Free Energy

In the microbial realm, energy is the currency of life, measured in the rhythmic beats of kilojoules (kJ), a unit that resonates with the heat energy released during chemical reactions. Within this energetic dance, microbiologists are particularly attuned to the strains of free energy (G), the maestro orchestrating cellular work.

1. Delta G: Harmonizing Energy Changes
The melodic notes of energy changes find expression in ∆G₀, where ∆ symbolizes "change in." The duet of "o" and "prime" signifies that this free energy value unfolds under "standard" conditions: a harmonious pH of 7, a temperature ballet at 25°C, and reactants and products twirling at an initial concentration of 1M.

• Exergonic Rhythms: If the ∆G₀ is a negative tune, the microbial ensemble proceeds with the release of free energy, a cadence that may be conserved in the treasury of adenosine triphosphate (ATP). These energy-yielding melodies are known as exergonic reactions.

• Endergonic Serenades: In contrast, if the ∆G₀ is a positive sonnet, the reaction seeks an infusion of energy, an endergonic duet that requires a musical offering of energy to proceed.

2. Free Energy of Formation: Crafting Molecular Melodies

In the orchestration of microbial symphonies, the free energy of formation (GOF) serenades the energy yielded or required for the creation of a molecule from its elemental constituents. Elements, in their pure essence, dance with a GOF of zero.

• Energetic Ballet: As compounds form exergonically, their GOF is cast in negative hues, reflecting the release of energy. Conversely, endergonic dances carry a positive GOF, signifying the energy investment.

3. Energetic Scores: Calculating the Harmonic Shifts
In the sheet music of microbial reactions, calculating the ∆G₀ involves subtracting the sum of the GOF of reactants from that of products. For a dance like A + B → C + D:

ΔG₀ of A + B → C + D = GOF[C + D] – GOF[A + B]

4. Energetic Ensemble: Harmonies and Anomalies
As we glance at Table 23.1, the GOF values for compounds weave a tapestry of energy dynamics. The majority sway with negative GOF, an ode to spontaneous formation. Yet, the positive GOF for nitrous oxide (N₂O; +104.2 kJ/mol) croons a different tune, signaling its reluctance to form spontaneously, preferring the path of decomposition to nitrogen and oxygen.

In the microbial theater of energy, the ledger is a testament to the dance of free energy, orchestrating reactions, shaping pathways, and crafting the symphony of life.

Microbial Orchestra: Redox Symphony

In the vibrant world of microbiology, the symphony of life is conducted through the captivating interplay of oxidation-reduction (redox) reactions. These rhythmic dances involve the graceful exchange of electrons, where a generous electron donor pirouettes with a willing electron acceptor.

1. The Dance Partners: Reductant and Oxidant

In this duet, the electron donor takes the spotlight as the reducing agent or reductant, offering its electrons. The electron acceptor, playing the role of the oxidising agent or oxidant, gracefully welcomes these electrons. The redox reaction is elegantly presented:

Oxidant + n^e− ⇌ Reductant

2. The Energetic Waltz: Electron Donors and Acceptors

The performance of redox reactions is a choreography where electrons released by the donor must find a worthy dance partner, the acceptor. A dance like the oxidation of hydrogen gas (H₂) unveils its first act:

H₂ → 2^e− + 2H⁺

This is but a prelude, awaiting the second act where an electron acceptor like O₂ engages in a reduction reaction:

1/2O₂ + 2^e− + 2H⁺ → H₂O

Together, these half reactions compose the harmonious composition:

H₂ + 1/2O₂ → H₂O

In this dance, H₂ is the electron donor (oxidised), and O₂ is the electron acceptor (reduced).

3. The Harmonic Scale: Reduction Potentials
The reduction potentials (E₀') are the musical notes expressing substances' inclination to be oxidised or reduced. These potentials, measured in volts or millivolts, narrate a substance's tendency. For example, hydrogen (H₂) at pH 7 boasts a reduction potential of -0.42 volts, marking its eagerness to donate electrons.

4. The Melodious Couples: Redox Pairs
In this ballet of electrons, molecules can switch roles, acting as either donors or acceptors. Redox couples, representing these dual identities, are elegantly composed. For example, in the redox couple 2H⁺ / H₂, H₂ tends to donate electrons, while in ½ O₂ / H₂O, O₂ craves to accept electrons.

5. The Electron Tower: Imaginary Symphony
Behold the electron tower, a grand metaphorical structure representing the range of reduction potentials. The highest point embodies the strongest electron donors, descending gracefully down to the eager electron acceptors at the bottom. O₂ reigns supreme at the base, coveted by organisms for its willingness to accept electrons.

In this grand electron orchestra, redox couples in the middle can sway between roles, acting as either donors or acceptors. The electron tower narrates the tales of energy released as electrons cascade down, creating a harmonious interplay of microbial life.

Electron Carriers

In the mesmerizing world of microbial choreography, the graceful transfer of electrons steals the spotlight in oxidation-reduction reactions. This dance unfolds through intermediaries known as electron carriers, leading the electrons from a primary donor to a terminal acceptor.

1. Dance Partners: Primary and Terminal
In this dance, the initial electron donor is the esteemed primary electron donor, setting the stage for the grand performance. The terminal electron acceptor, eagerly awaiting its role, concludes the dance with finesse.

2. Harmonizing Reduction Potentials

The elegance of the dance lies in the harmony of reduction potentials (E₀'). The net change in free energy (∆G₀) is dictated by the difference in E₀' between the primary electron donor and the terminal electron acceptor, composing a symphony of energy flow.

3. Distinguished Carriers: Freely Diffusible and Membrane-Associated

The carriers emerge in two groups, each contributing its unique rhythm to the dance:

(a) Freely Diffusible Carriers

• NAD⁺ and NADP⁺: Coenzymes that navigate freely, the nicotinamide ring of NAD⁺ and NADP⁺ becomes the canvas for a captivating electron-painting. Accepting two electrons and one proton from a donor, they release a second proton, orchestrating a dance of redox potential at -0.32 volts.

(b) Membrane-Associated Carriers

• NADH Dehydrogenases, Flavoproteins, Cytochromes, and Quinones: These carriers, firmly attached to enzymes in the cytoplasmic membrane, wear the costumes of flavin mononucleotide (FMN), flavin-adenine dinucleotide (FAD), cytochromes, nonheme iron-sulphur (Fe/S) proteins, and quinones. Their choreography spans the membrane, creating an electrifying performance.

4. NAD⁺ vs. NADP⁺: A Tale of Roles

While both NAD⁺ and NADP⁺ boast the same reduction potentials, their roles in the cellular drama differ. NAD⁺/NADH takes center stage in energy-generating (catabolic) reactions, captivating the audience with its prowess. On the other hand, NADP⁺/NADPH plays a crucial role in the backstage of biosynthetic (anabolic) reactions, crafting the cellular narrative.

In this microbial ballet of electron carriers, each participant plays a pivotal role, ensuring the flow of energy orchestrates the symphony of life.

Nonheme Iron-Sulphur and Quinones

In the electrifying performance of microbial electron transport, two distinguished dancers, Nonheme Iron-Sulphur (Fe/S) Proteins and Quinones, take the center stage, adding complexity to the choreography.

1. Nonheme Iron-Sulphur (Fe/S) Proteins: Masters of Arrangement
These electron-carrying proteins, devoid of a heme group, earn the title of Nonheme Iron-Sulphur (Fe/S) Proteins. The dance floor witnesses various arrangements, with Fe₂S₂ and Fe₄S₄ clusters emerging as the stars. Iron atoms, partners in this rhythmic ensemble, form bonds with free sulfur and the protein itself, creating a captivating dance of electrons and cysteine residues.

• Ferredoxin, a prominent member of this group with an Fe₂S₂ configuration, entrances the audience in photosynthetic electron transport and other electron transport processes. The wide range of reduction potentials exhibited by these proteins allows them to perform at different points in the electron transport process, complementing the diversity of the microbial dance.

2. Quinones: Hydrophobic Maestros
Meet the hydrophobic virtuosos known as Quinones, non-protein entities seamlessly integrated into the dance of electrons. These membrane-associated molecules boast high hydrophobicity and serve as both electron donors and proton acceptors. Among them, Coenzyme Q (CoQ) or ubiquinone stands out, orchestrating the movement of electrons and protons in respiratory electron transport processes.

In bacterial realms, some quinones share kinship with vitamin K, a growth factor for higher animals, adding a touch of intrigue to their role in the microbial saga.

3. Conservation of Energy: The Grand Finale
As the dance reaches its climax, the energy released during these electrifying oxidation-reduction reactions finds its sanctuary in high-energy phosphate bonds. The grand finale features high-energy compounds such as phosphoenolpyruvate, 1,3-bisphosphoglycerate, ATP, ADP, and the illustrious thio-ester bonds of coenzyme A (CoA) derivatives like acetyl-CoA.

In the microbial dance of elements, these performers, Nonheme Iron-Sulphur Proteins and Quinones, exemplify the intricate interplay of chemistry and biology, unveiling the captivating symphony of energy flow.

ATP and CoA: Guardians of Cellular Energy

In the bustling city of cellular life, two guardians stand at the forefront, wielding the power of high-energy compounds to drive the dynamic processes within.

1. Adenosine Triphosphate (ATP): The Energy Maestro
At the heart of cellular energy management lies Adenosine Triphosphate (ATP), a molecular masterpiece. Comprising adenosine and a trio of phosphate partners, ATP orchestrates the symphony of life. Notably, two of its three phosphate bonds are anhydride bonds, brimming with high free energies of hydrolysis. As ATP gracefully transforms into Adenosine Diphosphate (ADP) and orthrophosphate (Pi), it releases a surge of free energy. This energy, akin to a cellular currency, fuels biosynthetic reactions and propels the intricate dance of cellular functions.

2. Coenzyme A (CoA) Derivatives: Sustaining the Energetic Flow
Enter the Coenzyme A (CoA) derivatives, exemplified by the illustrious Acetyl-CoA. These compounds boast thio-ester bonds, distinct from the phosphoanhydride bonds found in ATP. In the grand interplay of energy conservation, CoA derivatives contribute significantly. Hydrolysis of these thio-ester bonds releases a torrent of energy, driving the synthesis of high-energy phosphate bonds, especially in the realm of anaerobic microorganisms engaged in fermentation.

• Acetyl-CoA, a notable CoA derivative, takes the spotlight as a versatile participant in energy metabolism and the synthesis of fatty acids. Its structure, adorned with a thio-ester bond, epitomizes the potential for energy conservation in the microscopic world.

3. Options for Energy Conservation: Catabolism and Anabolism
In the grand theater of metabolism, two captivating acts unfold: catabolism and anabolism. Catabolism steals the spotlight, portraying the breakdown of complex molecules into simpler forms, a process liberating energy for cellular use. Like a controlled cascade, this energy finds its way into the cellular coffers, becoming a valuable resource.
On the flip side, anabolism takes center stage, crafting intricate molecules from simpler components. In this upward surge of synthesis, energy is invested to weave the tapestry of cellular complexity.
Together, ATP and CoA derivatives emerge as essential guardians, navigating the ebb and flow of energy within the cellular domain, ensuring the vitality of life's grand performance.