In: Biology
Early in the course we spent time talking about carbohydrates, proteins, nucleic acids and lipids. All of these are synthesized through condensation reactions.
A. What is a condensation reaction?
B. Why do condensation reactions require energy? Use concepts such as potential energy and entropy in your answer.
C. Describe the link between spontaneous/nonspontaneous reactions and energy.
A) A condensation reaction is a class of organic addition reaction, in which a complex molecule is formed from its simpler subunits and water is released as a byproduct. Because of release of water this reaction got its name, it is also known as dehydration reaction. Synthesiz of major biological macro-molecules such as carbohydrates, proteins, fatty acids and nucleic acids are the result of condensation reactions. All these macro molecules are synthesized from single subunits called their monomer (for example, amino acids for proteins, nucleotides for nucleic acids etc). The monomers combine together using covalent bonds to form larger molecules called polymers by releasing water molecules. This joining of one monomer to the other occurs by combining the hydrogen of one monomer (-H) with the hydroxyl group (-OH) of another monomer, releases one molecule of water (H2O).
B) Entropy is the measure of degree of randomness or disorder of a system. Entropy of a well organized system is low and entropy of a disorganized system is high. When speaking in terms of chemical reactions, entropy increases when a substance is broken up into multiple parts. So condensation reaction is arranging single monomers into a polymer. Hence its entropy is decreasing as a result of condensation. Also during condensation reactions, new covalent bonds are forming between monomers. Hence it requires energy. It is because the potential energy of atoms decreases when they are bonded to other atoms than when they are separated.
C) Reactions are favourable when the enthalpy of the system is low and entropy of the system is high. When both of these conditions are met, a reaction occurs naturally and it is called a spontaneous reaction. Whereas a non-spontaneous reaction is a reaction that does not favour the formation of products under the given set of conditions. Many chemical reactions release energy which can be used to do other processes (coupling of reactions). A spontaneous reaction releases free energy. Where as a non-spontaneous (endergonic) reaction is a chemical reaction in which the standard change in free energy is positive and energy is absorbed.