Proteins are probably the most versatile of all the organic molecules, making up many structures and executing various functions within organisms. Building blocks called amino acids make up proteins. About 20 different amino acids combine to form all of the various types of proteins on Earth. These amino acids all have almost the exact same composition; the only difference is the R group, which differs in each of the amino acids and gives them their uniqueness.
duration - the period of time during which something continues. continuance. period, period of time, time period - an amount of time; a time period of 30 years; hastened the period of time of his recovery; Picasso's blue period. clocking - the time taken to traverse a measured course; it was a world record clocking.
a period of unusually warm weather in the autumn. the period of time that it takes for a planet (as, e.g., Earth or Mars) to make a complete revolution around the sun. the period of instruction in a school; the time period when school is in session. a period of time containing 365 (or 366) days. a period of time occupying a regular part of a calendar year that is used for some particular activity. half a year; a period of 6 months.