Question

Palade granules are
A. Glycoprotein particles
B. Pigment granules
C. Excretory vesicles
D. Ribosomes

Answer 1

Hint: Palade granules are discovered by George palade in 1953 in the animal cell. They are the dense particles present in the cytoplasm observed under the electron microscope.

Complete answer:
Palade granules are also known as ribosomes. Ribosomes are composed of rRNA and proteins and are not surrounded by any membrane.
The ribosomes are composed of two units. One ribosomal subunit is large in size and has a dome-like shape and the other ribosomal subunit is smaller in size and placed above the larger subunit and forms a cap-like structure. The two ribosomal subunits remain united with each other due to specific concentration of the magnesium ion.
Ribosomes are of two types:
70S ribosomes: It is made up of ribonucleoproteins in the ratio of 60: 40 (RNA: Protein). 70S ribosomes are consists of:
30S smaller subunit: 21 protein molecules and 16S rRNA.
50S larger subunit: 34 protein molecules and 23S and 5S rRNA.
80S ribosomes: It is made up of ribonucleoproteins in the ratio of 40: 60 (RNA: Protein). 80S ribosomes are consists of:
40S smaller subunit: 33 protein molecules and a single 18S-rRNA.
60S larger subunit: 40 protein molecules and three types of rRNAs- 28S, 5.8S and 5S.

Functions of ribosomes:
They are the sites of protein synthesis.
The free ribosomes synthesize non-secretory proteins.
The ER bound ribosomes synthesize secretory proteins.

So the correct answer is option D.

Note: During protein synthesis, many ribosomes form a chain on a common messenger RNA and form the polyribosomes or polysomes or ergasome. These organelles are also known as protein factories.