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24 Cards in this Set

  • Front
  • Back
What are the 4 life or death consequences for cells controlled by signals?
1) Survival
2) Growth and division
3) Differentation
4) Programmed death (apoptosis)
Where are most receptors located?
at the cell surface
Why are signals important?
Signals tell cell whether they are in the right environment and whether it is appropriate to divide or differentiate in that environment. Normal cells removed from correct environment usually die.
What are the 4 forms of intracellular signaling?
1) Contact dependent
2) Paracrine (signals released into extracellular space and act locally on neighbor cells)
3) Synaptic
4) Endocrine
What are three types of cell-surface receptors?
1) Ion channel-linked
2) G-protein linked
3) Enzyme linked (tyrosine kinases)
In what type of signaling pathways is phosphorylation required?
Activation of both enzyme-linked and Gprotein-linked pathways
What is the role of phosphatases?
TOpposes phosphorylation in signalizing pathways by turning off signals as rapidly as they are turned on.
How is adenlylyl cyclase activated?
the alpha subunit of the trimeric G-protein detaches upon exchanging GTP for GDP and binds to an activating site on adenylyl cyclase
What does activated adenlylyl cyclase produce, and what does this compound activate in turn?
cAMP, then cAMP activates A-kinase, which elevates glucose levels by breaking down stored glycogen.
Besides adenlylyl cyclase, what can G-protein receptors stimulate formation of?
Phospholipase C-Beta, which then targets PIP2. PIP2 is then cleaved into IP3 and diacylglycerol as second messengers.
What does IP3 do?
Opens gated Ca++ release channels in the ER membrane, which binds to and activates calmodulin, which in turn activates breakdown of glycogen (Just like A-kinase!!!)
Most growth factor receptors have what kind of activity in their cytoplasmic domains?
tyrosine-specific protein kinase activity
What is an important secondary signaling molecule in enzyme-linked signal transduction?
Phopholipase C-gamma, which cleaves PIP2 into IP3 and diacylglycerol (like G-protein-linked receptors).
What do Receptor Tyrosine Kinases indirectly activate through intermediate proteins?
The monomeric protein ras.
What role does GEF (Guanine nucleotide exchange factor) play in ras activation?
GEF activates ras by cuasing it to exchange GTP for GDP.
What protein inactivates ras and how?
GAP (GTPPase activating protein) inactivates ras by causing it to hydrolyze GTP to GDP.
ras activates the first kinase in a cascade of ________.
Cytoplasmic serine/threonine kinases
What are two signal transduction pathways, besides G-protein linked and Receptor tyrosine kinases?
Cytokine receptor (used by myeloid and lymphoid cells)
integrin/cadherin junctional proteins (cell/matrix and cell/cell junctions)
What is interesting about cytokine receptor and RTK pathways?
They can overlap at the ras-kinase cascade pathway activated by RTKs.
What can activate transcription factors and send signals to the nucleus involving integrin receptors?
Junctional activation of ras.
What is the significance of a junction sending signals to the nucleus?
The structural assembly of focal adhesions and stress fibers in cell attached to matrix plays a feedback, regulatory role by telling the cell that it is attached to matrix in teh proper location. Helps cell survive and provide permission for cell to grow and divide.
What are two important functions of beta-catenin?
1) helps link actin or intermediate filaments to cell-cell junctions
2) can move into nucleus and activate transcription factors the stimulate cell cycle is not bound up in junctions
What are two ways to prevent cytoplasmic veta-catenin from entering the nucleus and stimulating cell division?
a) APC (cytoplasmic protein that bind catenin and gets it degraded in proteasome
b) Cell-cell junctions
How are the effects of integrin and cadherin junctions opposite?
Cell-matrix junctions are permissive for cell division whereas cell-cell junctions are inhibitors of cell division.