Protein biosynthesis occurs in –
**Core Concept**
Protein biosynthesis is the process by which cells create proteins from amino acids, involving transcription of DNA into messenger RNA (mRNA) and translation of mRNA into a polypeptide chain. This process occurs in specific cellular organelles.
**Why the Correct Answer is Right**
Protein biosynthesis primarily takes place in the ribosomes, which are complex molecular machines composed of ribosomal RNA (rRNA) and proteins. Ribosomes read the sequence of codons on the mRNA and assemble the corresponding amino acids into a polypeptide chain through a process known as translation. The ribosomes are located on the rough endoplasmic reticulum (RER) in eukaryotic cells, but the actual protein synthesis occurs within the ribosomes. The ribosomes are the site where the genetic information encoded in the mRNA is used to synthesize proteins.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because protein biosynthesis does not primarily occur in the nucleus, where DNA transcription to mRNA takes place, but rather in the ribosomes.
**Option B:** This option is incorrect because the endoplasmic reticulum (ER), both rough and smooth, is involved in protein modification, folding, and transport, but not in the primary process of protein biosynthesis.
**Option C:** This option is incorrect because the mitochondria are involved in protein synthesis, but only for mitochondrial proteins and not for the majority of cellular proteins.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that ribosomes are the site of protein synthesis, and their dysfunction can lead to various diseases, including ribosomal disorders and certain types of cancer.
**Correct Answer:** C.