The nucleic acids DNA and RNA are composed of smaller...

Name: Problem 82, Chapter 17: Chemistry
Uploaded: 2020-07-08T20:02:48-08:00
Duration: 2 min 43 s
Channel: Ronald Prasad
Description: The nucleic acids DNA and RNA are composed of smaller repeating units called nucleotides. The reaction to form a phosphate-ester linkage between two nucleotides can be approximated as follows: Would you predict the formation of a dinucleotide from two nucleotides to be a spontaneous process? How can you justify the existence of nucleic acids in light of the second law of thermodynamics?

The nucleic acids DNA and RNA are composed of smaller repeating units called nucleotides. The reaction to form a phosphate-ester linkage between two nucleotides can be approximated as follows: Would you predict the formation of a dinucleotide from two nucleotides to be a spontaneous process? How can you justify the existence of nucleic acids in light of the second law of thermodynamics?

The nucleic acids DNA and RNA are composed of smaller repeating units called nucleotides. The reaction to form a phosphate-ester linkage between two nucleotides can be approximated as follows:
Would you predict the formation of a dinucleotide from two nucleotides to be a spontaneous process? How can you justify the existence of nucleic acids in light of the second law of thermodynamics?

Key Concepts

Phosphate-Ester Bond Formation

Phosphate-ester bonds, which link nucleotides together in nucleic acids, are formed via phosphorylation reactions. The formation of these bonds is thermodynamically unfavorable on its own, but is made feasible in biological systems by coupling the reaction with the hydrolysis of energy-rich molecules (e.g., pyrophosphate), thereby making the overall process favorable.

Second Law of Thermodynamics

The second law of thermodynamics states that the entropy, or disorder, of an isolated system tends to increase over time. In biological systems, local decreases in entropy (such as the formation of ordered polymers like nucleic acids) are possible when they are offset by increases in the entropy of the surroundings, ensuring that the overall entropy of the universe increases.

Gibbs Free Energy

Gibbs free energy is the thermodynamic potential that determines whether a reaction can occur spontaneously. A negative free energy change (?G) signals that the process is thermodynamically favorable, while a positive ?G indicates that the reaction is non-spontaneous under standard conditions.

Energy Coupling

Energy coupling refers to the biological strategy of linking an endergonic (non-spontaneous) reaction to an exergonic (spontaneous) one. In many biochemical processes, including nucleic acid synthesis, unfavorable reactions are driven by coupling them to reactions that release sufficient energy to overcome overall energetic barriers.

Condensation Reactions

Condensation reactions involve the joining of two molecules with the simultaneous release of a small molecule, such as water or pyrophosphate. This type of reaction is characteristic of polymerization processes like the formation of nucleic acids and is generally endergonic, requiring energy input or coupling to an exergonic reaction.

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