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.
The Certificate of Postgraduate Study is a research course requiring one year full-time or five terms' part-time study in Cambridge. It is normally taken as the probationary year of a PhD. It is not usual for applicants to apply directly to this course.