Insulin receptors are

Options

A. extrinsic proteins
B. intrinsic proteins
C. G-proteins
D. trimeric proteins.

Answer

**Step-by-Step Solution:**

1. **Understanding Insulin Receptors**: Insulin receptors are proteins that play a crucial role in the regulation of glucose levels in the blood. They are responsible for binding insulin, a polypeptide hormone, which initiates a series of cellular responses.

2. **Identifying the Structure of Insulin Receptors**: Insulin receptors are composed of two main subunits: the alpha subunit and the beta subunit. These subunits are linked together by disulfide bonds.

3. **Classifying Insulin Receptors**: When categorizing proteins, they can be classified as either intrinsic or extrinsic proteins. Extrinsic proteins are those that are not embedded within the lipid bilayer of the cell membrane, while intrinsic proteins are embedded within the membrane.

4. **Determining the Type of Insulin Receptor**: Since insulin receptors are not embedded in the lipid bilayer but rather are located on the extracellular surface of the cell membrane, they are classified as extrinsic proteins.

5. **Reviewing Other Options**:
- **Intrinsic Proteins**: These are firmly embedded in the phospholipid layer and are not applicable to insulin receptors.
- **G-Proteins**: These are involved in signal transduction but are not the same as insulin receptors.
- **Trimeric Proteins**: These refer to proteins formed by three non-covalently bound macromolecules, which does not describe insulin receptors.

6. **Conclusion**: Based on the structure and classification, insulin receptors are correctly identified as extrinsic proteins.

**Final Answer**: Insulin receptors are extrinsic proteins.

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