BIOL 1108 Study Guide - Midterm Guide: Cell Adhesion Molecule, Cell Adhesion, Integrin
Document Summary
Only eukaryotes have developed macroscopic bodies with functionally differentiated tissues. Simple multicellularity occurs most prominently among algae. The functional challenge of complex multicellularity is transporting food, oxygen, and molecular signals rapidly across large distances within the body. Diffusion is effective only over short distances. Diffusion exerts a strong constraint on the size, shape, and function of cells due to the fact that it supplies key molecules for metabolism. Animals achieve large size by circumventing limits imposed by diffusion. We circumvent diffusion by actively pumping oxygen rich blood through our bodies, which is possible because oxygen binds to molecules of hemoglobin in red blood cells and then is carried through the bloodstream to distant sites of respiration. Complex multicellular organisms have structures specialized for bulk flow. Cadherins, integrins, and additional transmembrane proteins provide the molecular mechanisms for adhesion in animals, but in plants they synthesize cell adhesion molecules that are polysaccharides called pectins.
