Question

Smooth Endoplasmic reticulum of an animal cell does not synthesize
A) Cholesterol
B) Phospholipid
C) Saturated fatty acids
D) Unsaturated fatty acids

Answer 1

The endoplasmic reticulum is a network of membranous structures within eukaryotic cells. Rough ER is continuous with the nuclear envelope, and is responsible for the production of proteins. Smooth ER is involved in lipid synthesis.

Complete answer:
Smooth endoplasmic reticulum is involved in the synthesis of steroids. These include the synthesis of steroid hormones from the precursor cholesterol. Cells that do produce steroids have a large network of smooth endoplasmic reticulum. Smooth ER produces cholesterol, option A is incorrect.
Phospholipids are molecules that contain glycerol, two fatty acids, and a phosphate head group. The cytosolic surface of the endoplasmic reticulum has the enzymes involved in phospholipid synthesis. Option B is not the correct answer.
Fatty acid synthesis occurs in the cytoplasm of cells. They start from the precursor molecule Acetyl CoA which comes from the mitochondria. Fatty acids are synthesised initially in the saturated from, with no double bonds. Therefore, the smooth endoplasmic reticulum does not synthesise saturated fatty acids. Option C is the correct answer.
From saturated fatty acids, by conversion of bonds between particular carbon atoms from single to double, unsaturated fatty acids are produced. The enzymes responsible for this process are present in the smooth endoplasmic reticulum. Option D is incorrect.

Hence the correct answer is option ‘C’.

Note: Along with the Golgi complex, Smooth endoplasmic reticulum is involved with processing and packaging of components of the cell wall. It also produces unsaturated fatty acids, but cannot make all that are required by our bodies. Essential fatty acids like linoleic and oleic have to come from our diets.