29. In animals, four separates families of cell — cell adhesion proteins are listed in Column A and their functional characteristics are given in Column B
Which one of the following is the correct combination?
(1) a — (i), b— (ii), c— (iii), d — (iv)
(2) a— (ii), b— (iii), c— (iv), d — (i)
(3) a— (iii), b— (iv), c— (i), d — (ii)
(4) a— (iv), b— (iii), c— (ii), d — (i)
The correct combination is:
(1) a — (i), b — (ii), c — (iii), d — (iv)
This reflects the four separate families of cell-cell adhesion proteins in animals matched to their functional characteristics:
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a — Cadherins (i): Mediate calcium-dependent homophilic cell-cell adhesion, maintaining tissue integrity and involved in adherens junctions.
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b — Integrins (ii): Function primarily in cell-extracellular matrix adhesion, linking ECM proteins to the cytoskeleton and signaling.
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c — Selectins (iii): Bind carbohydrate ligands and mediate transient, heterophilic adhesion important in leukocyte homing and inflammation.
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d — Immunoglobulin superfamily proteins (iv): Mediate diverse cell-cell adhesion events through homophilic and heterophilic interactions, often calcium-independent, including roles in immune recognition.
Overview of Cell Adhesion Protein Families
Cell adhesion molecules (CAMs) mediate specific cell-cell and cell-matrix interactions crucial for tissue formation, immune responses, and cellular communication. Four major protein families perform these roles in vertebrates:
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Cadherins: Calcium-dependent, primarily homophilic cell-cell adhesion molecules involved in stable adhesive contacts.
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Integrins: Bind ECM components and transmit signals between the ECM and cytoskeleton.
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Selectins: Mediate transient, carbohydrate-dependent cell-cell adhesion under shear stress, especially in the immune system.
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Immunoglobulin superfamily proteins: Diverse adhesion receptors mediating both homophilic and heterophilic interactions, important in neural cell adhesion and immune functions.
Functions Table
| Family | Function |
|---|---|
| Cadherins (a) | Calcium-dependent homophilic adhesion, tissue integrity |
| Integrins (b) | Cell-ECM adhesion, signal transduction |
| Selectins (c) | Transient, carbohydrate-dependent adhesion in leukocyte trafficking |
| Immunoglobulin superfamily (d) | Ca2+-independent adhesion; cell-cell interactions in immunity and neural tissue |
Conclusion
The combination (1) a—(i), b—(ii), c—(iii), d—(iv) correctly aligns major animal cell adhesion protein families with their functional roles, reflecting a foundational concept in cell biology and tissue organization.
