Membrane proteins are

Options

A. cellulase
B. lyases
C. permeases
D. All of these

Answer

**Step-by-Step Solution:**

1. **Understanding Membrane Proteins:**
- Membrane proteins are proteins that are found on or within the plasma membrane of cells. They play crucial roles in various cellular functions.

2. **Types of Membrane Proteins:**
- Membrane proteins can be classified into different types:
- **Integral Proteins:** These proteins are embedded within the membrane and can span across the entire membrane (transmembrane proteins).
- **Peripheral Proteins:** These proteins are attached to the exterior or interior surfaces of the membrane but do not penetrate the lipid bilayer.

3. **Analyzing the Options:**
- The question provides four options: cellulase, lyases, permeases, and all of these.
- **Cellulase:** This is an enzyme that breaks down cellulose, not a membrane protein.
- **Lyases:** These are enzymes that catalyze the joining of two molecules by breaking double bonds, also not membrane proteins.
- **Permeases:** These are specific types of membrane proteins that facilitate the transport of certain molecules across the membrane.

4. **Identifying the Correct Answer:**
- Since cellulase and lyases are not membrane proteins, the only correct option that represents a type of membrane protein is **permeases**.

5. **Conclusion:**
- Therefore, the answer to the question "Membrane proteins are" is **permeases**.

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