CELL BIO FINAL EXAM!

• The GTPase Ras mediates signaling by most RTKs and is activated by growth factors
• An RTK activates Ras through indirect coupling of the activated receptor to a Ras GEF
• ~30% of human tumors express hyperactive mutant forms of Ras
• Transient activation of Ras revealed by single-molecule fluorescence resonance energy transfer (FRET)

  The experiment: Add Epidermal Growth Factor (EGF) and detect red light emission under UV
• The MAP kinase signaling module activated by Ras
• Rasrecruits Rafto the plasma membrane and helps activate it
• Activated genes includes those that stimulate cell division (e.g. G1 cyclins)
• The organization of two MAP kinase modules by scaffold proteinsin budding yeast

  • response to high osmolarity
  • mating response
• Cytokines: a class of immunoregulatoryproteins including some hormones and many local mediators (e.g. interferons)
• Cytokines activate gene regulatory proteinsthat are held in a latent state
• Cytokines activate these proteins through binding to the cytokine receptors
• Cytokine receptors do NOThave intrinsicenzymatic activity
• Cytosine receptors offer A more direct signaling route in gene expression control
• The JAK-STATsignaling pathway activated by cytokines
• JAK-STAT IS Signaled off by protein phosphatases
• receptor ser/thr kinases Represent an even more direct signaling pathway
• receptor ser/thr kinases Signaling molecules: hormones and local mediators that belong to thetransforming growth factor-β(TGF-β) superfamily
• receptor ser/thr kinase The TGF-β receptors activategene regulatory proteins directly at the plasma membrane
• The Smad-dependent signaling pathway activated by TGFβ
• SMADs:cytoplasmic gene regulatory proteins
• The proposed divergence of plant and animal lineages froma common unicellular eukaryoticancestor
• Multicellularity and cell communication evolve independentlyin plants and animals ●Diverged from the last common ancestor more than a billion years ago
• Cell communication in plants -Transmembrane cell-surface receptors, notably the serine/threonine kinases are commonly used (notably LRR receptor kinases)
• Plants uses fewG protein-coupled receptors
• Plant cells seem NOTto use receptor tyrosine kinases, steroid-hormone-type nuclear receptors, or cAMP
• The ethylene-mediated triple response that occurs when the growing shoot of a germinating seedling encounters an obstacle underground
• The triple response: -Thickens stem -Shields the tip (hook) -Reduces the shoot’s tendency to grow away from the direction of gravity (to bypass the obstacle)
• w/o ethylene: ubiquitination and destruction of EIN3
• Ethylene: inactivates the receptors
• The ethylene receptor is a serine/threonine kinase
• CTR1: resembles MAP KKK
• ethylene is a Dimeric transmembrane protein located in ER membrane
• Auxin receptor in the nucleus
• Auxin influences gene expression by controlling the degradation of transcription regulators
• Phytochromes: dimeric, cytoplasmic serine/threonine kinases
• Phytochromes =are an example of a photoreceptor that is found in the chloroplasts
• The cytoskeleton: an intricate network of protein filaments that extends throughout the cytoplasm
• cytoskeleton is Highly dynamic in structure
• the cytoskeleton is Being continuously reorganizedas cells change shape or divide
• the cytoskeleton contains Fiber-associated proteins