exMock Flashcards
Describe mechanisms by which transcriptional regulators are activated or inhibited.
Transcriptional regulators are activated by phosphorylation (e.g., CREB), ligand binding (e.g., glucocorticoid receptor), or dimerization (e.g., NF-κB). They are inhibited by repressor binding (e.g., LacI), histone deacetylation, or chromatin remodeling.
Explain the concept of cell memory and how it is maintained across cell divisions.
Cell memory is maintained through epigenetic modifications like DNA methylation (e.g., CpG islands) and histone modifications (e.g., H3K27me3 for repression). Positive feedback loops reinforce transcriptional states.
Outline the role of non-coding RNAs in gene expression regulation.
miRNAs inhibit translation by binding the 3’ UTR (e.g., let-7 and Ras), siRNAs degrade mRNA via RISC, and lncRNAs scaffold chromatin modifiers (e.g., Xist for X-inactivation).
Compare activation mechanisms of GPCRs and RTKs.
GPCRs activate via ligand binding, conformational change, and G-protein activation (e.g., β-adrenergic receptor). RTKs activate through ligand-induced dimerization and autophosphorylation (e.g., EGFR).
Explain the role of second messengers in intracellular signaling.
cAMP activates PKA to regulate glycogen metabolism, while Ca²⁺ binds calmodulin to activate kinases like CaMKII. Both amplify signals.
Describe the JAK-STAT pathway and its regulation.
Cytokine binding triggers JAK phosphorylation, STAT dimerization, and nuclear translocation. Regulation occurs through SOCS proteins and phosphatases to prevent excessive signaling.
Describe the phases of the cell cycle and their checkpoints.
G1 phase involves cell growth, G1/S checkpoint ensures DNA integrity. S phase is DNA replication, G2 phase prepares for mitosis, G2/M checkpoint verifies DNA replication. The M phase involves mitosis and cytokinesis, the spindle checkpoint ensures chromatid alignment.
Discuss the role of cyclin-dependent kinases (Cdks) and cyclins in cell cycle progression.
Cdks are activated by binding cyclins (e.g., Cdk1-cyclin B for mitosis). Their activity is regulated by phosphorylation and CKIs like p21.
Outline the role of APC/C in mitosis.
APC/C ubiquitinates securin, activating separase to cleave cohesin and separate sister chromatids during anaphase.
Explain actin filament nucleation and treadmilling.
Actin nucleation involves Arp2/3 for branched filaments and formin for unbranched filaments. Treadmilling is ATP-actin polymerization at the barbed end and ADP-actin depolymerization at the pointed end.
Describe microtubule structure and function in intracellular transport.
Microtubules are hollow tubulin dimers with dynamic instability. Kinesins move cargo to the + end, and dyneins transport to the − end.
Discuss how Rho and Rac regulate cell movement.
Rho promotes stress fiber formation for contraction, while Rac stimulates lamellipodia formation for forward movement.
Differentiate between apoptosis and necrosis.
Apoptosis involves membrane blebbing, caspase activation, and DNA fragmentation. Necrosis causes cell swelling, membrane rupture, and inflammation.
Describe the intrinsic pathway of apoptosis.
Pro-apoptotic proteins Bax and Bak form mitochondrial pores, releasing cytochrome c, which forms the apoptosome with Apaf-1 to activate caspase-9 and initiate apoptosis.
Explain the extrinsic pathway of apoptosis.
Death receptors (e.g., Fas) bind ligands, activating caspase-8. This pathway is essential for immune regulation, removing infected or cancerous cells.
