Which of the following membrane has the highest protein content per gram tissue:
First, I recall that different biological membranes have varying compositions of lipids and proteins. The core concept here is understanding the relative proportions of proteins and lipids in different membranes. For example, mitochondrial membranes might have more proteins because they have a lot of enzymes involved in the electron transport chain and ATP synthesis. The inner mitochondrial membrane is known to have a high protein-to-lipid ratio, maybe around 1:1 by weight, compared to other membranes like the plasma membrane, which might have a lower ratio, like 1:4 or 1:5.
Wait, but the question asks for the highest protein content per gram of tissue. So, if a membrane has a higher protein content by weight, that would mean more proteins relative to lipids. The inner mitochondrial membrane is highly folded (cristae) and packed with proteins, so per gram of tissue, it's likely to have a higher protein content. Other membranes like the myelin sheath might have more lipids because they're specialized for insulation, thus lower protein content. The plasma membrane might have a moderate amount. So the answer should be the inner mitochondrial membrane.
Now, the options might include things like inner mitochondrial membrane, plasma membrane, myelin sheath, outer mitochondrial membrane. The correct answer is the inner mitochondrial membrane. The incorrect options would be the others. The clinical pearl here is knowing that membranes with high metabolic activity (like mitochondria) have higher protein content. This is important for exams because it's a common question about membrane composition.
**Core Concept**
Biological membranes vary in protein-to-lipid ratios depending on their functional specialization. Membranes with high metabolic activity, such as those involved in energy transduction, typically have higher protein content to accommodate enzymes and transporters. The inner mitochondrial membrane is a classic example due to its role in oxidative phosphorylation.
**Why the Correct Answer is Right**
The **inner mitochondrial membrane** has the highest protein content (~1:1 protein-to-lipid ratio by weight) because it houses the electron transport chain complexes, ATP synthase, and numerous transport proteins. Its structural complexity (cristae) and metabolic demands necessitate a dense packing of proteins for ATP production and ion transport.
**Why Each Wrong Option is Incorrect**
**Option A:** *Plasma membrane* – Typically has a 1:2 protein-to-lipid ratio, lower than the inner mitochondrial membrane.
**Option B:** *Myelin sheath* – Rich in lipids (>70% lipids by weight) for insulation, not proteins.
**Option C:** *Outer mitochondrial membrane* – Has a 1:4 protein-to-lipid ratio, lower than the inner membrane due to fewer metabolic proteins.
**Clinical Pearl**
Membranes with high energy demands (e.g., mitochondria) have the highest protein density. Remember: **"Mitochondria = Powerhouse → Protein Powerhouse"** for NEET/USMLE.
**Correct Answer: C. Inner mitochondrial membrane**