A signal reaches a cell mostly in the form of a signalling molecule binding to a receptor on the cell surface. This binding activates a chain of events that amplifies the signal and transfers it inside the cell. Protein kinases phosphorylate proteins and cause their activation or deactivation, or in general modify their activity. When a signalling molecule binds to a receptor, a cascade is activated and the second messengers, such as cAMP, are synthesized. cAMP molecules activate the protein kinases, which phosphorylate specific proteins and activate them.
The characteristics that bryophytes share with algae are biflagellate motile gametes and the life cycle. The life cycle, of course, is the duration of the life of the object. Biflagellate motile gametes are made when two or more of the motile gametes fuse into a zygote.
The thickness of the uterine lining , becomes very thick...because when the level of hormone progesterone reaches its highest levels. according to Dr.X on yahoo answers.
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A eukaryotic cell has far more organelles and most prominently, has a nucleus. A prokaryotic cell stores it's DNA in it's cytoplasm.
