7. Which of the following is not an extracellular matrix protein
   (1) Globin (2) Elastin
   (3) Collagen (4) Fibronectin

Introduction to Extracellular Matrix Proteins

The extracellular matrix (ECM) is a crucial biological network of proteins and macromolecules that provides both structural and biochemical support to surrounding cells. The ECM helps organize tissues, enables cell communication, and plays vital roles in development, wound healing, and tissue regeneration.​

Key ECM Proteins: Collagen, Elastin, Fibronectin

Collagen

Collagen is the most abundant ECM protein, offering structural strength and tensile support to tissues. Different types of collagen build up various tissues like skin, bones, tendons, and the basement membrane.​

Elastin

Elastin provides tissues with elasticity and resilience, allowing organs such as the skin, lungs, and blood vessels to stretch and recoil. It is mainly synthesized by fibroblasts and smooth muscle cells.​

Fibronectin

Fibronectin is a glycoprotein that mediates cell attachment to the ECM and supports tissue repair and wound healing. It acts as a connector between structural ECM components and integrins on the cell surface.​

Globin: Not an ECM Protein

Globin proteins, such as hemoglobin and myoglobin, are primarily found inside cells—especially red blood cells. They transport oxygen throughout the body and play no structural or adhesive role in the extracellular matrix. Their absence from the ECM is clear since they do not contribute to tissue architecture or support.​

ECM Protein Functions and Importance

• Collagen: Provides tensile strength and is the main protein in connective tissue.​

• Elastin: Allows tissue to stretch and return to its original shape.​

• Fibronectin: Facilitates cell adhesion, migration, wound healing, and links cells to matrix components.​

• Globin: Functions intracellularly for oxygen transport and does not participate in ECM structure or support.​

ECM Proteins Table

Conclusion

• Globin is not an extracellular matrix protein; it functions inside cells and is unrelated to ECM structure.

• Collagen, elastin, and fibronectin are central ECM proteins, each with critical structural or adhesive functions in tissue biology.​

• Understanding ECM protein composition is fundamental for grasping how tissues develop, function, and repair.