Gwendolyn Quintana @01187235 04.16.131. How do cells prevent crosstalk between kinase pathways, i.e. once. In a real situation, cross-talk is common to most cells, commonly by cross-talk using cross-presentation of proteins within signal transduction cascades. Many times phosphorylation and G-coupled proteins areligand specific or have cAMP requirements that can distinguish the specific amplification of a phosphorylation cascade molecule as opposed to a neighboring signal transduction cascade. 2. Compare Ras and the G proteins as to activation/inactivation by GTP. In the off state Ras is bound to GDP. In the on state Ras is bound to GTP. Ras is a G-protein and can be phosphorylated. Regulation of g-proteins in the active state, the alpha subunit is bound to the GDP in a complex with beta and hormone binding stimulates the release of GDP and its exchange for GTP. The activated bound GTP alpha subunit and other subunit then dissociates from the receptor and interacts with the receptor and their target. Activity of the alpha subunit is terminated by hydrolysis of GTP and the inactive GDP bound alpha subunit then reassociates with the beta complex. Ras is converted to the active GTP bound state by exchange of GTP for bound DP, which is stimulated by guanine nucleotide exchange factors (GEFs). Ras activity is then terminated by GTP hydrolysis which is stimulated by GTPaseactivating proteins (GAPs). 3. In human cancer, is the Ras protein activity enhanced or inhibited? Explain. In human cancer, the Ras protein activity is enhanced. Ras/Raf lies upstream to kinase pathways such as ERK. ERK part of an evolutionarily conserved pathway that regulates cell differentiation, cell survival, andcell proliferation. Hence, in the upregulation of Ras/Raf there is an increase in cell differentiation, survival, and cell proliferation. 4. What relationship/association or similarity does Ras have to PI-3 kinase? Extracellular ligands such as growth factors (GF) or insulin bind receptors that activate signal-transduction pathways involving Ras and PI 3-kinase (PI 3-K). They both lie on the same pathway; PI 3-K is downstream of Ras. Likewise, they are both kinases and elicit the continuation of a phosphorylation cascade upon signal recognition. They are both involved in the MAPK signal transduction pathway. 5. G0 = cell cycle arrestM= mitosis G1= interval between mitosis and DNA replication ; cell growth S= DNA replication G2= cell growth continues and proteins synthesized in preparation for mitosis6. Cyclin B synthesized and complexes with existing Cdk1 during G2. Cdk1 phosphorylaiton at Thr-161 is required for activity and also phosphorylated at Try-15 and Thr-14, which inhibits action by Cdk1:complex during G2. M phase initiated by Cdc25C phosphatase that dephosphorylates Cdk1= Cdk1: cyclin act = (1) M phase (2) triggers degradation cyclin B via Ubiquination.7. Compare normal adult cell mitosis and embryonic cell mitosis. In adult cells there are all stages of mitosis. In embryonic cells there is G1 and G2 lacking with a short S and M phase. 8. MCM helicase only bind in G1 to replication origins together with ORC proteins following DNA replication beginning in phase, MCM gets displaced to ensure DNA replication cannot occur. 9. Define cell cycle checkpoints. G2 unreplicated of damagen DNA . in M – chromosome misalignment (spindle assembly checkpoint). In S – unreplicated or damaged DNA; in G1 – damaged DNA.10. List the different kinds of microtubules and give the function of each in the cell cycle. There are astral, kinetochore, chromosomal, and polar microtubules. Astral microtubules originate from the centrosome and don’t connect to a kinetochore; they make the actin skeleton and interact with the cell cortex to aid in spindle orientation. Kinetochore microtubules are on the chromatids where the spindle fibers attach during cell division to pull sister chromatids apart. Chromosomal microtubules do not attach to define kinetochores , but, in all stages, extend all the way from the chromatin to the pole. Polar microtubules are used with molecular motors and are attached to a microtubule from either side at the place where the polar microtubules overlap. During metaphase and anaphase the motors push the microtubules away in opposite directions. As this happens, the microtubules polymerize and get longer. The result is an elongation of the