What is meant by signal amplification? Provide two examples. What will be an ideal response?
Signal amplification occurs when a signaling molecule bound to a receptor produces changes
in millions of molecules in a cascade of reactions within the cell.. This observation explains
how just a few signal molecules, i.e., neurotransmitters, ions or hormones molecules can lead
to a major response by a cell.
Epinephrine binding to a G-protein receptor activates adenyl cyclase which catalyzes the
production of many cAMP molecules. Then each cAMP activates many protein kinases down
the cascade of reactions.
The Ras/MAP kinase is stimulated by epidermal growth factor binding to tyrosine kinase
receptor. This binding leads to activation of the G small protein. Ras then activates MAPkinase
signaling pathway. A series of MAP kinases in the pathway are then activated by
phosphorylation.
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Protists and bacteria are grouped into different domains because _____
A) protists eat bacteria B) bacteria are not made of cells C) protists have a membrane-bounded nucleus, which bacterial cells lack D) bacteria decompose protists E) protists are photosynthetic
Slow cooking for a long time and then storage at room temperature would tend to favor the growth of
A. endospore-formers. B. anaerobes. C. mesophiles. D. thermophiles. E. endospore-formers AND mesophiles.
Because of some of the problems with explaining how the first RNA organisms originated, an alternative possibility
has been proposed in which ____.
a. proteins and RNA evolved simultaneously b. DNA existed before RNA c. lipids functioned as enzymes d. a different form of life existed before the RNA world e. viruses functioned as carriers for RNA
The evolution of life on Earth was made possible by ____
a. DNA b. organelles
c. an environment that favors oxygen photosynthesizers d. natural selection that favors efficient reproduction of organisms e. random mutations