Which one of the following statements about proteins in mammalian cells is correct?

In mammalian cells, protein synthesis occurs on ribosomes, which are found either free in the cytoplasm or attached to the endoplasmic reticulum [4]. When ribosomes are attached to the endoplasmic reticulum, it is referred to as the rough endoplasmic reticulum (RER) [3]. The RER is a primary site for the synthesis of proteins, particularly those destined for secretion, incorporation into the cell membrane, or delivery to lysosomes [2]. While dietary proteins are absorbed as amino acids in the small intestine [2], the cell uses these building blocks to synthesize its own proteins based on genetic information. The Golgi apparatus subsequently modifies and packages these newly synthesized proteins but does not synthesize them [4]. Therefore, the statement that proteins are synthesized in the rough endoplasmic reticulum is correct.

Sources

1. [4] Science , class X (NCERT 2025 ed.) > Chapter 8: Heredity > 8.2.3 How do these Traits get Expressed? > p. 131
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Activity 5.3 > p. 86
3. [3] Science-Class VII . NCERT(Revised ed 2025) > Chapter 9: Life Processes in Animals > Small Intestine > p. 126
4. [1] https://www.sciencedirect.com/topics/medicine-and-dentistry/endoplasmic-reticulum-membrane