ex22new Flashcards
Gene expression in cells of multicellular eukaryotes is regulated at several levels and often depends on signaling from neighboring cells. How can neighboring cells affect gene expression?
Neighboring cells affect gene expression through signaling mechanisms such as Notch signaling, where Notch binds Delta leading to nuclear transcription changes, and Wnt signaling, where Wnt stabilizes β-catenin to regulate gene expression.
How is the mRNA level in the cytosol of a eukaryotic cell regulated?
mRNA levels are controlled through transcriptional regulation, mRNA degradation (via deadenylation and decapping), small RNA-mediated silencing (miRNAs/siRNAs), and mRNA localization for spatial protein synthesis.
Explain how alternative splicing and processing of mRNA can affect the function of the encoded protein.
Alternative splicing generates isoforms with distinct domains, affecting function, while processing steps like capping, polyadenylation, and editing regulate mRNA stability, localization, and protein diversity.
Why has the GPCR family expanded in humans compared to yeast, and how is this advantageous?
GPCR expansion in humans is driven by the need to sense complex environmental stimuli (e.g., light, odors). This enables advanced sensory detection and physiological regulation critical for multicellular complexity.
How is GPCR signaling activated and inactivated?
GPCR signaling is activated by ligand binding, causing G-protein activation via GDP-GTP exchange, and inactivated by GTP hydrolysis, receptor phosphorylation by GRKs, and arrestin binding.
How do GPCRs enable white blood cells to detect and move toward infection sites?
Chemokines bind GPCRs, activating Rac and Rho GTPases that reorganize the cytoskeleton, driving actin polymerization and chemotaxis toward the infection site.
How does regulated proteolysis control key processes during the cell cycle?
Proteolysis ensures unidirectional progression by degrading cyclins via APC/C and cleaving cohesin to separate chromatids during anaphase.
How do BCL2 family proteins operate and contribute to cancer development?
BCL2 family proteins regulate apoptosis by controlling mitochondrial membrane permeability. Overexpression of anti-apoptotic members (e.g., BCL2) inhibits apoptosis, promoting tumor survival.
What are the similarities and differences in cell-cell communication between animals and plants?
Both use signaling molecules and direct communication pathways (e.g., gap junctions in animals, plasmodesmata in plants), but animals rely on faster neurotransmitter-based signaling, while plants depend on slower phytohormonal mechanisms.
How do mutations in the retinoblastoma (Rb) gene lead to cancer?
Rb mutations disrupt its ability to inhibit E2F transcription factors, leading to uncontrolled S-phase entry and cell proliferation, as seen in retinoblastoma and other cancers.
