37. Which statement is correct for globular proteins?
    (1) Always contain only α helix
    (2) Always contain only β sheets
    (3) Contains more reverse turns
    (4) Contains α helix, β sheets and reverse turns

Structure and Characteristics of Globular Proteins

Globular proteins are the most functionally diverse class of proteins, playing key roles in enzymatic activity, transport, and cellular signaling. Understanding their structural elements is crucial for CSIR NET Life Science aspirants.

Correct Answer:

The correct option is (4) Contains α-helix, β-sheets, and reverse turns.

Explanation:

(1) Always Contain Only α-Helix ❌

• While some globular proteins (e.g., myoglobin) are predominantly α-helical, others contain β-sheets or a mix of both.
• Hence, this statement is incorrect.

(2) Always Contain Only β-Sheets ❌

• Some proteins like immunoglobulins have a β-sheet-rich structure, but most globular proteins contain a combination of α-helices and β-sheets.
• Thus, this statement is incorrect.

(3) Contains More Reverse Turns ❌

• While reverse turns (β-turns) are common in globular proteins to connect α-helices and β-sheets, they do not dominate the structure.
• Therefore, this statement is incorrect.

(4) Contains α-Helix, β-Sheets, and Reverse Turns ✅

• Most globular proteins have a mixed secondary structure, containing:
  • α-helices for structural stability.
  • β-sheets for core formation.
  • Reverse turns for flexibility and compact folding.
• Examples: Hemoglobin, Lysozyme, and Enzymes like Chymotrypsin.
• Since this statement is true, it is the correct answer.

Nearby Topics for Better Understanding

1. Structure of Globular Proteins

• Compactly folded into spherical shapes.
• Contains hydrophobic cores and hydrophilic exteriors.
• Found in enzymes, antibodies, and transport proteins.

2. Comparison of Protein Classes

3. Importance of Reverse Turns in Protein Folding

• Connects different secondary structures.
• Increases protein flexibility.
• Found in loop regions of enzymes and binding sites.

4. Functional Roles of Globular Proteins

• Enzymes (e.g., DNA polymerase, amylase).
• Transport Proteins (e.g., Hemoglobin, Albumin).
• Structural Proteins (e.g., Actin in the cytoskeleton).

Conclusion

Globular proteins exhibit a diverse mix of α-helices, β-sheets, and reverse turns, making them functionally versatile. Understanding their structure is essential for CSIR NET Life Science aspirants.