Considering your answers to Exercises 142 and 143, how can you justify the existence of proteins and nucleic acids in light of the second law of thermodynamics?

The second law of thermodynamics states that in any isolated system, the entropy (which represents disorder or randomness) always increases over time, or in reversible processes, remains constant. This law defines the natural tendency of processes in the universe to move towards states of higher disorder.

Proteins and nucleic acids are complex biological molecules that play essential roles in living organisms. Proteins are polymers of amino acids and are involved in various cellular functions such as catalysis, transport, and structural support. Nucleic acids, like DNA and RNA, are polymers of nucleotides and contain genetic information, regulating gene expression and protein synthesis.

Biological systems are not isolated systems. In fact, they constantly exchange energy and matter with their surroundings. For example, living organisms extract energy from food, which is converted into chemical energy within the cells. This chemical energy is used to perform various biological processes like the synthesis of proteins and nucleic acids.

Gibbs free energy is a thermodynamic quantity that represents the maximum reversible work that can be done by a system at constant temperature and pressure. In biological reactions, a decrease in Gibbs free energy ∆G indicates that a reaction is favorable and can occur spontaneously. The change in Gibbs free energy is given by: \(∆G = ∆H – T∆S\) Where: ∆G = Gibb's free energy change ∆H = enthalpy change T = temperature of the system ∆S = entropy change

When complex molecules like proteins and nucleic acids are synthesized, the overall Gibbs free energy change of the system must be negative for these reactions to occur spontaneously. This means that the decrease in entropy associated with the formation of these molecules is more than compensated by other factors like the release of energy in the form of heat or the absorption of energy by surrounding molecules. For instance, the energy released by breaking down ATP into ADP and inorganic phosphate during cellular processes might compensate for the decrease in entropy.

While the formation of complex molecules like proteins and nucleic acids might seem to contradict the second law of thermodynamics, it is crucial to consider the system as a whole. When energy is released as heat, it disperses throughout the environment, increasing the entropy of the surroundings. This increase in environmental entropy can be greater than the decrease in entropy associated with the formation of proteins and nucleic acids, thus satisfying the second law of thermodynamics. In conclusion, although the formation of proteins and nucleic acids seems to contradict the second law of thermodynamics, it is essential to consider the overall system, including the input of energy and increase of the environmental entropy. This way, the existence of these complex biological molecules can be justified in light of the second law of thermodynamics.