Question

Protein synthesis occurs in
(А) Mitochondria
(B) Chloroplasts
(C) Cytoplasm
(D) All of the above

Answer 1

Hint: Protein synthesis is defined as the process in which amino acids get arranged in linear order into proteins. The synthesis of protein involves all types of RNAs including ribosomal RNA, messenger RNA and transfer RNA. Protein synthesis also involves use of certain enzymes.

Complete answer:
Ribosomes are sites of protein synthesis. The free ribosomes are involved in the synthesis of nonsecretory proteins while the Endoplasmic reticulum that binds ribosomes synthesize secretory proteins. Free ribosomes are involved in synthesising structural and enzymatic proteins for use inside the cell. The attached ribosomes synthesise proteins for transport. Thus, these organelles are also known as protein factories. Newly synthesized proteins are processed with the help of chaperons protein.
Now let us match this with given options:-
Mitochondria :- The matrix of mitochondria contains a single circular of DNA molecule (with high $G=C$ content), a few RNA molecules and 70s ribosomes and the components required for the synthesis of proteins. The matrix also contains enzymes for TCA (Tricarboxylic acid) cycle.
Chloroplast :- In both prokaryotic and eukaryotic cells, a semi-fluid matrix called cytoplasm occupies the volume of the cell. The cytoplasm is defined as the main arena of cellular activities in both the plant and animal cells. Ribosomes are present in cytoplasm.
Cytoplasm :- It is made up of extremely minute, fibrous, filamentous and tubular proteinaceous structures which form the structural framework inside the cell. The cytoskeleton occurs only in eukaryotic cells and is involved in many functions such as protein synthesis , mechanical support motility, maintenance of the shape of the cell.
All of these :- as ribosomes are present in mitochondria , chloroplast and cytoplasm all these structures are involved in protein synthesis. Thus this option is correct.

Our required answer is D) All of these.

Note:
The ribosomes are composed of two subunits. One ribosomal subunit is always large in size and has a shape like that of the dome , and the other ribosomal subunit is smaller in size and occurs above the larger subunit and forms a cap-like structure. The two ribosomal subunits remain united with each other due to a specific concentration of the $$M{g}^{2+}$$ ions. When the concentration of $$M{g}^{2+}$$ ions reduces below a critical level both ribosomal subunits get separated. But, by raising the concentration of $$M{g}^{2+}$$ ions in the matrix, the two ribosomes become associated with each other and is known as the dimer.