MCAT Biological and Biochemical Foundations of Living Systems Flashcards: 1a Nonenzymatic Protein Function

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This deck focuses on 1a Nonenzymatic Protein Function, 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: What is the primary nonenzymatic function of cell-surface receptors (e.g., GPCRs, RTKs)?

Answer: Ligand binding that initiates signal transduction pathways. These receptors detect extracellular signals and transmit them intracellularly, regulating processes like metabolism and growth.

Flashcard 2: What is the nonenzymatic function of MHC class I molecules?

Answer: Present endogenous peptides to $CD8^+$ T cells. MHC I displays intracellular peptides on cell surfaces, allowing cytotoxic T cells to detect and eliminate infected or abnormal cells.

Flashcard 3: What is the primary nonenzymatic function of cadherins?

Answer: Mediate calcium-dependent cell–cell adhesion. Cadherins form adherens junctions via homophilic interactions, stabilized by calcium, to maintain tissue structure and polarity.

Flashcard 4: What is the nonenzymatic function of the T cell receptor (TCR)?

Answer: Bind peptide–MHC complexes to initiate T cell signaling. TCRs recognize antigenic peptides on MHC, triggering T cell activation and adaptive immune responses.

Flashcard 5: What is the main nonenzymatic function of antibodies (immunoglobulins)?

Answer: Bind specific antigens for immune recognition and neutralization. Antibodies' variable regions specifically recognize antigens, facilitating immune responses like opsonization and complement activation.

Flashcard 6: What is the primary nonenzymatic function of ferritin inside cells?

Answer: Store iron in a soluble, nonreactive form. Ferritin's shell sequesters excess iron ions, preventing oxidative damage and providing a releasable store for cellular needs.

Flashcard 7: What is the primary nonenzymatic function of transferrin in blood?

Answer: Transport $Fe^{3+}$ in plasma. Transferrin binds ferric iron tightly to prevent toxicity while delivering it to cells via receptor-mediated endocytosis.

Flashcard 8: What is the nonenzymatic function of albumin in plasma?

Answer: Maintain oncotic pressure and carry hydrophobic molecules. Albumin's abundance in blood regulates osmotic pressure and its binding sites transport lipids, hormones, and drugs.

Flashcard 9: What is the primary nonenzymatic function of myoglobin?

Answer: Store $O_2$ in muscle cells. Myoglobin's single heme group binds oxygen with high affinity, serving as a reservoir for rapid release during muscle activity.

Flashcard 10: What is the primary nonenzymatic function of hemoglobin?

Answer: Transport $O_2$ in blood (and assist $CO_2/H^+$ handling). Hemoglobin's heme groups reversibly bind oxygen, enabling efficient delivery to tissues while also modulating pH and carbon dioxide.

Flashcard 11: What is the nonenzymatic function of dynein and kinesin?

Answer: ATP-driven motor transport along microtubules. These motor proteins use ATP hydrolysis to walk along microtubules, facilitating vesicle and organelle transport in cells.

Flashcard 12: What is the nonenzymatic function of tubulin in eukaryotic cells?

Answer: Form microtubules for structure, transport, and chromosome segregation. Tubulin dimers polymerize into hollow tubes essential for cellular architecture, intracellular transport, and mitotic spindle formation.

Flashcard 13: What is the main nonenzymatic function of actin and myosin in muscle?

Answer: Force generation and contraction via filament sliding. In muscle contraction, actin thin filaments and myosin thick filaments interact to produce movement through cross-bridge cycling.

Flashcard 14: What is the nonenzymatic function of chaperone proteins such as Hsp70?

Answer: Assist protein folding and prevent aggregation. Chaperones stabilize nascent polypeptides and refold misfolded proteins, ensuring proper conformation without catalyzing reactions.

Flashcard 15: What is the primary nonenzymatic function of integrins?

Answer: Mediate cell–ECM adhesion and bidirectional signaling. Integrins link extracellular matrix to cytoskeleton, enabling adhesion, migration, and signal exchange for tissue organization.

Flashcard 16: What is the nonenzymatic function of MHC class II molecules?

Answer: Present exogenous peptides to $CD4^+$ T cells. MHC II presents antigens from extracellular pathogens to helper T cells, coordinating immune responses like antibody production.

Flashcard 17: What is the primary nonenzymatic function of selectins?

Answer: Mediate transient cell–cell adhesion (leukocyte rolling). Selectins' carbohydrate-binding domains enable weak, reversible interactions for leukocyte recruitment during inflammation.

Flashcard 18: What nonenzymatic role do ligand-gated ion channels perform?

Answer: Open/close to allow ion flux in response to ligand binding. Ligand binding induces conformational changes in these channels, controlling membrane potential and cellular signaling.

Flashcard 19: What is the primary nonenzymatic role of keratin in epithelial cells?

Answer: Mechanical protection and structural integrity (intermediate filaments). Keratin forms resilient filaments that protect epithelial cells from mechanical stress and maintain tissue architecture.

Flashcard 20: What is the key nonenzymatic function of elastin in tissues?

Answer: Provide elasticity and recoil. Elastin's cross-linked structure allows tissues like arteries and lungs to stretch and return to shape without damage.

Flashcard 21: What is the major structural protein of the extracellular matrix in connective tissue?

Answer: Collagen. As the most abundant protein in connective tissues, it provides a scaffold for cells and resists tensile forces.

Flashcard 22: What is the primary nonenzymatic function of structural proteins like collagen?

Answer: Provide tensile strength and structural support to tissues. Structural proteins form frameworks that resist mechanical stress, enabling tissues to withstand tension and maintain integrity.

Flashcard 23: What is the defining feature of a nonenzymatic protein function?

Answer: A protein role not involving catalysis of a chemical reaction. Enzymatic functions specifically catalyze reactions, whereas nonenzymatic roles encompass all other protein activities like binding or support.

Flashcard 24: What is the primary nonenzymatic function of transcription factors?

Answer: Bind specific DNA sequences to regulate gene expression. Transcription factors' DNA-binding domains interact with promoters or enhancers, modulating RNA polymerase activity for gene control.