Question

The site of protein synthesis is
a. Ribosomes
b. DNA
c. Nucleus
d. Mitochondria

Answer 1

Hint: Proteins are linear chains of amino acids linked by peptide bonds. These are manufactured by the structures that are found in both prokaryotic and eukaryotic organisms and present in two units large and small.

Complete answer:
Protein synthesis takes place in ribosomes.
These are granular structures found in both the prokaryotes and eukaryotes. The formation of ribosomes is done by two subunits one large and another is small. In prokaryotes, ribosomes are made up of two subunits, the 50S, and 30S, which together form 70S prokaryotic ribosomes. Eukaryotic ribosomes are of 80S type.

Fig.- Ribosome

Additional Information:
Ribosomes that are present in the matrix synthesize a protein that remains inside the cell, whereas ribosomes on the plasma membrane form proteins that are transported outside the cell. The ribosomes of polysomes translate mRNA into protein. In Eukaryotes, free ribosomes synthesize non secretory proteins, structural and enzymatic proteins which remain inside the cell. While ER bound ribosomes form secretory proteins that can be transported outside the cell. A network of tiny tubular structures is found scattered in the cytoplasm known as Endoplasmic Reticulum in eukaryotic cells. It helps in the division of the intracellular space into two distinct compartments, i.e., luminal (inside ER) and extraluminal (cytoplasm) compartments. The endoplasmic reticulum that has ribosomes present on their surface is called rough endoplasmic reticulum (RER). When no ribosomes present, they appear smooth and are called smooth endoplasmic reticulum (SER). RER helps in the protein production in cells. The smooth endoplasmic reticulum is the major site for synthesis of lipids. In animal cells SR synthesize lipid-like steroidal hormones.

So the correct answer is Ribosomes.

Notes:
- The credit of ribosome discovery is given to George Pallade.
- ‘S’ is Svedberg’s Unit which stands for sedimentation coefficient, a measure of density and size.
- Mitochondria and chloroplast have similar ribosomes of the 70S as present in bacteria.
- Ribosomes are one of the few structures that are common in bacteria and animals.