BIOMOLECULES AND ENZYMES

Detailed explanation-1: -There are two major types of GTP-binding proteins-large trimeric GTP-binding proteins (also called G proteins), which relay the signals from G-protein-linked receptors (see Figure 15-15B), and small monomeric GTPases (also called monomeric GTP-binding proteins).

Detailed explanation-2: -Signaling proteins that bind directly to the phosphorylated tyrosines on IRS-1 include the adaptor proteins, Shc and Grb-2, and the p85 subunit of PI-3 kinase.

Detailed explanation-3: -Cells typically communicate using chemical signals. These chemical signals, which are proteins or other molecules produced by a sending cell, are often secreted from the cell and released into the extracellular space. There, they can float – like messages in a bottle – over to neighboring cells.

Detailed explanation-4: -Gap junctions are the main site of cell-cell signaling or communication that allow small molecules to diffuse between adjacent cells. In vertebrates, gap junctions are composed of transmembrane proteins called connexins.

Detailed explanation-5: -Many proteins contain several of these domains and can bind multiple partners simultaneously. Because of this multiplicity of binding domains, proteins can often form complexes to facilitate the flow of information through a signalling pathway.