Question

Which one of the following biomolecules is synthesized in a smooth endoplasmic reticulum?
(a) Proteins
(b) Lipids
(c) Carbohydrates
(d) Nucleotides

Answer 1

Hint: The smooth endoplasmic reticulum lacks the presence of ribosomes on its surface which gives it a smooth appearance. The ribosomes are protein-producing structures. The smooth endoplasmic reticulum is found in abundance in the hormone-producing cells.

Complete step by step answer:
The smooth endoplasmic reticulum(SER) is the main site for the synthesis of essential lipids such as phospholipids and cholesterol. Both phospholipid and cholesterol together help in maintaining the formation of the cell membrane and in maintaining the structure and shape of the cell and the cell membrane.
Other forms of lipids that are produced by smooth endoplasmic reticulum are steroids. The steroid-secreting cells such as adrenal glands contain smooth endoplasmic reticulum in abundance for the secretion of different hormones. There are many types of hormones secreted by the adrenal gland, however, they can be classified into three major hormones- Glucocorticoids, Mineralocorticoids, and sex hormones. These are majorly synthesized by cholesterol. Cholesterol is converted into a number of steroids by the enzyme activity of cytochromes.

Additional information:
Endoplasmic Reticulum is a cell organelle which is a network of tiny tubular structures scattered in the cytoplasm of a eukaryotic cell. It is present in almost all the eukaryotic cells except RBCs, embryonic cells, and ova. It is classified into two types based on the presence or absence of ribosomes on its surface.
Rough Endoplasmic Reticulum: The ribosomes are present on the surface and it mainly helps in the production of proteins. It helps in protein folding and protein sorting. It delivers the protein to the Golgi apparatus which performs packaging of the protein molecules into vesicles and its transportation inside and outside the cell.
Smooth endoplasmic reticulum: The ribosomes are absent on the surface of the endoplasmic reticulum. It just has a tubular form. The function of smooth endoplasmic reticulum varies depending on the type of cell.
So, the correct answer is '(b) Lipids'.

Note: Smooth endoplasmic reticulum also helps in transporting the products of the rough endoplasmic reticulum to other organelles, especially the Golgi apparatus as it is usually present closer to the cell membrane and cytoplasm and the rough endoplasmic reticulum is closer to the nucleus.
- SER helps in the storage and release of calcium ions which play a major role in the nervous system and the muscular system.
- SER also metabolizes carbohydrates.