Your cells contain two types of nucleic acids, ribonucleic acid and deoxyribonucleic acid, or RNA and DNA, respectively. They differ from the other macronutrients in that they are not a source of calories in your diet, and their role is strictly to direct the synthesis of new protein molecules.
The definition of a postgraduate is a student who is studying a subject beyond the college level when he already has a college degree. Someone attending medical school is an example of a postgraduate.
A doctorate degree, such as a Doctor of Philosophy (Ph.D), is considered the highest academic degree in a particular field of study in some countries, including the United States. These degrees are considered terminal because there is no higher degree that can be awarded.