MCAT Biological and Biochemical Foundations of Living Systems Flashcards: 2a Cell Cell Junctions Ecm

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This deck focuses on 2a Cell Cell Junctions Ecm, giving you a quick way to review the definitions, rules, and examples that matter most for MCAT Biological and Biochemical Foundations of Living Systems.

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Flashcard 1: Identify the junction type: Ca$^{2+}$-dependent cadherins connect cells to actin belts.

Answer: Adherens junction. This junction forms a belt-like structure for circumferential adhesion and cytoskeletal linkage.

Flashcard 2: What is the basement membrane (basal lamina) primarily composed of?

Answer: Laminin, type IV collagen, proteoglycans, and nidogen. These components form a thin, organized sheet separating epithelia from connective tissue.

Flashcard 3: Which protein subunits assemble to form a connexon in a gap junction?

Answer: Connexins. Six connexins form a hemichannel (connexon) that docks with an adjacent cell's to create the pore.

Flashcard 4: What is the primary function of tight junctions (zonula occludens) in epithelia?

Answer: Seal adjacent cells to block paracellular transport and maintain polarity. They form a barrier at the apical-lateral border, preventing diffusion between cells and separating membrane domains.

Flashcard 5: What is the primary function of desmosomes (macula adherens)?

Answer: Strong cell–cell adhesion resisting mechanical stress. They distribute mechanical forces across tissues by anchoring intermediate filaments between cells.

Flashcard 6: What is the primary function of hemidesmosomes?

Answer: Anchor epithelial cells to the basement membrane (ECM). They provide stable attachment to the underlying ECM, maintaining epithelial integrity.

Flashcard 7: What is the typical maximum size limit for molecules passing through gap junctions?

Answer: Approximately $< 1$ kDa. The channel pore size restricts passage to small solutes, ensuring selective communication.

Flashcard 8: Which cytoskeletal element is anchored at adherens junctions?

Answer: Actin microfilaments. Catenins link cadherins to the actin cytoskeleton, enabling force transmission and cell shape maintenance.

Flashcard 9: What is the key function of adherens junctions (zonula adherens) between cells?

Answer: Cell–cell adhesion via actin-linked cadherins. They provide mechanical linkage and maintain tissue integrity by connecting cytoskeletons of neighboring cells.

Flashcard 10: What cytoskeletal element is linked to tight junctions via ZO proteins?

Answer: Actin microfilaments. ZO proteins act as scaffolds connecting transmembrane components to the cytoskeleton for structural support.

Flashcard 11: Which basement membrane protein forms a sheet-like network and binds integrins?

Answer: Laminin. It self-assembles into networks that organize basement membranes and support epithelial attachment.

Flashcard 12: Which intermediate filaments are classically anchored to desmosomes in epithelia?

Answer: Keratin intermediate filaments. These filaments provide tensile strength and resilience, linking to desmosomes via plaque proteins.

Flashcard 13: What is the main function of the extracellular matrix (ECM) in animal tissues?

Answer: Structural support, signaling, and regulation of cell behavior. ECM provides a scaffold for cells, influences differentiation, and modulates growth factor activity.

Flashcard 14: What is a proteoglycan in the ECM?

Answer: Core protein covalently linked to glycosaminoglycan (GAG) chains. This structure allows proteoglycans to attract water and ions, contributing to ECM hydration.

Flashcard 15: Which transmembrane receptor links hemidesmosomes to the extracellular matrix?

Answer: Integrins. These receptors bind ECM ligands like laminin, connecting to intracellular adapters.

Flashcard 16: Which cadherin-family proteins are the transmembrane components of desmosomes?

Answer: Desmoglein and desmocollin. These proteins form transcellular dimers, anchoring cytoskeletal elements for robust adhesion.

Flashcard 17: Which ECM protein is the major tensile-strength component of connective tissue?

Answer: Collagen. Its triple-helical structure resists stretching, forming fibrils that support tissue architecture.

Flashcard 18: Identify the junction type: protein channels allow ion flow and electrical coupling.

Answer: Gap junction. It facilitates rapid signaling and synchronization in tissues like cardiac muscle.

Flashcard 19: Which Ca$^{2+}$-dependent adhesion proteins mediate adherens junctions?

Answer: Cadherins (for example, E-cadherin). These proteins homophilically bind across cells in a calcium-dependent manner to facilitate adhesion.

Flashcard 20: What is the defining feature of integrins regarding ligand binding and signaling?

Answer: Bidirectional signaling: inside-out and outside-in. Integrins transmit signals from ECM to cytoskeleton and vice versa, regulating adhesion and migration.

Flashcard 21: Which transmembrane proteins form the sealing strands of tight junctions?

Answer: Claudins and occludin. These proteins create the tight seal by forming extracellular interactions between adjacent cell membranes.

Flashcard 22: Which ECM protein commonly mediates cell attachment by binding integrins (RGD motif)?

Answer: Fibronectin. It links cells to collagen via integrin-binding domains, facilitating migration and organization.

Flashcard 23: Which cytoskeletal element is anchored by hemidesmosomes inside the cell?

Answer: Intermediate filaments (keratin). They link to plaque proteins like plectin, providing mechanical stability against shear forces.

Flashcard 24: Which ECM component provides hydration and resistance to compression in cartilage?

Answer: Proteoglycans and GAGs (for example, aggrecan, hyaluronan). Their negatively charged GAGs bind water, creating a hydrated gel that absorbs compressive forces.

Flashcard 25: What is the primary function of gap junctions between animal cells?

Answer: Direct intercellular passage of ions and small molecules. They enable metabolic and electrical coupling by forming aqueous pores between cytoplasms.