Crosstalk Signaling Pathways or Signaling Webs

Cell biologists often talk of signaling pathways in which a transmitter activates a chain of events culminating in an effect. The vertical arrows in Figure 16.12 show four signaling pathways that we have discussed in this chapter. We have already seen one example of Figure 16.11. PIP3 recruits protein kinase B (PKB) to the plasma membrane, where it is activated. Active PKB has many effects including exocytosis of vesicles containing glucose carriers and inac-tivation of BAD. Figure 16.11. PIP3...

Making Fatty Acids And Glycerides

All cells need fatty acids for membrane lipids. Fat cells make large amounts of fat (triacyl-glycerols) in times of plenty. The basic machinery is a multienzyme complex (in bacteria) or a multidomain protein (in eukaryotes) that uses the substrate acetyl-CoA. In both cases the growing fatty acid chain is not released it swivels from enzyme to enzyme or domain to domain in the array, adding two carbons for each complete cycle until the limiting length of 16 carbons is reached The product,...

The Initial Velocity of an Enzyme Reaction

The basic experiment in the study of enzyme behavior is measurement of the appearance of product as a function of time Fig. 11.5 . This is often called an enzyme assay. The product appears most rapidly at the very beginning of the reaction. As the reaction progresses, the rate at which the product appears slows down and eventually becomes zero when the system has reached equilibrium. All reactions are in principle reversible thus the observed overall rate of the reaction is actually the...