Atomic and Molecular structure
An atom is made up of protons, neutrons and electrons. Protons are positively charged and they denote the atomic number. Neutrons have no electrical charge. Protons and neutrons are present in the nucleus. Electrons are negatively charged and present in the orbits surrounding the nucleus. Isotopes have same number of protons but different number of neutrons. Loss or gain of electrons is seen in ions. Sharing electrons form covalent bond in molecules. Hydrogen bond is a type of intermolecular attraction among polar molecules such as water.
Types of organic molecules
Organic molecules are those derived from living organisms and they all contain carbon backbones. There are 7 major classes of organic molecules categorized by their functional groups: alcohols, aldehydes, ketones, carboxylic acids, amines, organic phosphates and thiols. Four major groups of macromolecules in cells are polysaccharides, proteins, nucleic acids and lipids. Each of these macromolecules is built up on smaller molecules.
Acids, basis and buffers
Acids are electrolytes that release hydrogen ions in water. Bases are electrolytes that release hydroxyl ions in water that can combine with hydrogen ions to form water. pH represents the concentration of hydrogen ions [H+] in solution (pH = -log [H+]). Buffer solutions are solutions which resist change in pH upon addition of small amounts of acid or base. Buffers provide a relatively stable environment for biochemical reactions to take place.
Like all other chemical reactions, biochemical reactions also favor DG negative reactions. Some reactions are DG positive and they can be coupled to other DG negative reactions in order to make the total DG of the coupled reaction to be negative. Nearly all biochemical reactions are catalyzed by enzymes, which decrease the activation energy but do not change the DG value of the reaction. Six major types of biochemical reactions are: oxidation-reduction, group transferring, hydrolysis, elimination or addition, isomerization and ligation of various groups. These reactions are catalyzed by corresponding enzymes: oxidoreductase, transferase, hydrolase, lyase, isomerase and ligase.