Maximum protein to lipid ratio is seen in –
**Core Concept**
The protein-to-lipid ratio in cell membranes is a crucial parameter that influences membrane fluidity and function. This ratio is an important determinant of the structural and functional properties of cellular membranes.
**Why the Correct Answer is Right**
The correct answer is **Sphingomyelin**. Sphingomyelin is a type of sphingolipid that contains a choline head group and a ceramide tail. It is a major component of mammalian cell membranes and is known to have a high protein-to-lipid ratio. This high ratio is due to the presence of a large protein component, such as the myelin sheath in the central nervous system, which is rich in sphingomyelin.
**Why Each Wrong Option is Incorrect**
**Option A:** Phosphatidylcholine is a type of phospholipid that contains a choline head group and a glycerol backbone. While it is a major component of cell membranes, it does not have a high protein-to-lipid ratio.
**Option B:** Cardiolipin is a type of phospholipid that contains four fatty acid chains and a phosphatidylglycerol backbone. It is found in the inner mitochondrial membrane and is not associated with a high protein-to-lipid ratio.
**Option C:** Lecithin is a mixture of phospholipids that contains a choline head group and a glycerol backbone. While it is a major component of cell membranes, it does not have a high protein-to-lipid ratio.
**Clinical Pearl / High-Yield Fact**
Sphingomyelin is an important component of the myelin sheath in the central nervous system, and its deficiency can lead to neurological disorders such as Krabbe disease.
**Correct Answer:** D. Sphingomyelin.