Chemical Reactions in Living Things

When making a nucleic acid like DNA or RNA, the phosphate group of one monomer binds covalently with the sugar group to make the polymer. The nitrogenous bases bind to each other loosely in hydrogen bonding to make the double helix seen in DNA. RNA is mostly single-stranded but can be double-stranded. In DNA, the adenine base binds with the thymine and the cytosine bonds with guanine, using hydrogen bonding to create the double strand. In RNA, the thymine is replaced with uracil.

Nucleic acids can also be messengers and energy-producing molecules. Adenosine triphosphate is an energy-producing molecule that has energy in the phosphate linkages so when ATP (adenosine triphosphate) becomes ADP (adenosine diphosphate) the phosphate link breakage releases energy that is used to drive reactions.

CHEMICAL REACTIONS IN LIVING THINGS

There are several types of reactions that can happen in biochemistry and cellular systems. One of these is a neutralization reaction. In this type of reaction, acids and bases react in order to form salt and water as a byproduct. The acids dissolve to make hydrogen or H+ ions. Bases dissolve in water to make hydroxyl or -OH ions. Neutralization reactions will control the pH of a solution by neutralizing the acidic and basic substances. Neutral pH in many systems is about 7 to 7.5, which is the pH that most enzymes react with the greatest intensity.

Condensation or dehydration reactions take two molecules or two parts of molecules, binding the molecules together and remove water from the equation. An example is when sugars make a glycosidic linkage, giving off water in the process.

Hydrolysis reactions are actually the reverse of condensation or dehydration reactions. Water is added to a system in order to divide or split two molecules or parts of molecules. Soap can be made by the hydrolysis of fats and corn syrup is made from the hydrolysis of corn starch.

An oxidation-reduction reaction or redox reaction, there is a change in the oxidation state of an atom. Oxidation means the atom has lost some electrons and reduction happens when the atom has gained some electrons. The reason that this is called a redox reaction is because they happen together. Oxidation always happens with reduction.

The reducing agent loses electrons and is oxidized, while the oxidizing agent gains electrons, becoming reduced itself. Applications of redox reactions include the reactions that happen in cellular respiration and photosynthesis. The production of free radicals can happen in these reactions. Free radicals can damage cellular structures.

The reactions that take place with enzymes will be discussed in a later chapter. Suffice it to say that enzymes reduce the energy of activation of a reaction so that the reaction can occur more easily. The beginning and ending energies of the reaction are the same with and without the enzyme. The enzyme just acts as a catalyst to facilitate the reaction. Without an enzyme, the reaction would occur too slowly.

Enzymes act like a lock and key, making the enzyme specific for a given substrate. The enzyme can change the orientation of a molecule in order to have a bond form, can change the placement of electrons to enhance the reactivity of the substrate, or can induce physical stress in order to cleave a molecule more easily. Enzyme activity can be affected by the concentration of the substrate and enzyme, by the pH, by pressure, and by temperature occurring at the time of the reaction. There can be competitive inhibition, whereby a substance or enzyme is blocked from reacting.