Which of the following elements are present in all proteins ? I. Carbon II. Hydrogen III. Oxygen IV. Nitrogen Select the correct answer from the codes given below : Codes :

Proteins are polymers of amino acids whose backbone and side chains are built from the elements carbon, hydrogen, oxygen and nitrogen. Textbook discussion of elemental composition in living matter highlights carbon, hydrogen and oxygen as the most abundant organic elements, and identifies nitrogen among the essential elements for life [1]. More specifically, nitrogen is an integral constituent of proteins (the amine group in amino acids), while sulphur occurs only in certain amino acids (e.g., cysteine, methionine), not universally in all proteins [2]. Educational resources on protein composition likewise summarize proteins as containing C, H, O and N as core elements (with S present in some proteins). Therefore all proteins contain I, II, III and IV.

Sources

1. [1] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 1: BASIC CONCEPTS OF ENVIRONMENT AND ECOLOGY > Carbon and Oxygen Cycles > p. 19
2. [2] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 25: Agriculture > Nitrogen (N) > p. 363