Cells involved in active protein synthesis have-
**Core Concept**
Cells involved in active protein synthesis have ribosomes, which are complex molecular machines responsible for translating messenger RNA (mRNA) into specific sequences of amino acids, thereby synthesizing proteins. This process is essential for cell growth, repair, and function.
**Why the Correct Answer is Right**
The correct answer involves ribosomes, which are composed of two subunits: the small subunit (40S) and the large subunit (60S). The small subunit recognizes the mRNA start codon and binds to the initiator transfer RNA (tRNA), while the large subunit catalyzes the peptide bond formation between amino acids. The ribosome reads the mRNA sequence and assembles the corresponding amino acids into a polypeptide chain. This process requires energy from the hydrolysis of GTP and is regulated by various factors, including initiation and elongation factors.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specifically mention cells involved in active protein synthesis. While cells with ribosomes are indeed capable of protein synthesis, this option is too vague and does not directly address the question.
**Option B:** This option is incorrect because it mentions the nucleus, which is the site of transcription, not translation. While the nucleus does contain the genetic material necessary for protein synthesis, the actual synthesis of proteins occurs in the cytoplasm, where ribosomes are located.
**Option C:** This option is incorrect because it mentions the mitochondria, which are involved in energy production through oxidative phosphorylation. While mitochondria do contain ribosomes, which are necessary for synthesizing mitochondrial proteins, they are not the primary site of active protein synthesis in cells.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the process of protein synthesis is tightly regulated by various mechanisms, including initiation and elongation factors, which ensure that the correct amino acids are assembled into the correct polypeptide chain. Disruptions in this process can lead to various diseases, including cancer and neurodegenerative disorders.
**Correct Answer:** D. Ribosomes