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AnP MIDTERM NOTES

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AnP MIDTERM NOTES Some Function of Plasma Membrane Proteins • Transport o Transport proteins create hydrophilic channels and are selective to which specific ion it is trying to transport, so a pr ... otein meant for Na will only transport Na and a protein meant for K will only transport K. o Some transport proteins hydrolyze ATP as an energy source to actively pump substances across the membrane • Intercellular Joining o Membrane proteins of adjacent cells may be hooked together in various kinds of intercellular junctions o Some membrane proteins provide temporary binding sites that guide cell migration and other cell-to-cell interactions • Enzyme Activity o A membrane protein may be an enzyme with its active site exposed to substances in the adjacent solution o A team of several enzymes in a membrane may catalyze sequential steps of a metabolic pathway. • Cell-Cell Recognition o Some glycoproteins serve as identification tags that are specifically recognized by other cells • Receptors for Signal Transduction o A membrane protein exposed to the outside of the cell may have a binding site that fits the shape of a specific chemical messenger, such as a hormone o When bound, the chemical messenger may cause a change in shape in the protein that initiates a chain of chemical reactions in the cell • Attachment to the Extracellular Matrix (ECM) o Elements of the cytoskeleton and the extracellular matrix may anchor to membrane proteins, which helps maintain cell shape ad fix the location of certain membrane proteins. o Others play a role in cell movement or bind adjacent cells together Cell Junctions • Tight Junctions – in a tight junction, a series of integral protein molecules in the plasma membranes of adjacent cells fuse together, forming an impermeable junction that encircles the cell. o Tight junctions prevent molecules from passing through the extracellular space between adjacent cells. • Desmosomes – these are anchoring junctions o Desmosomes are mechanical couplings scattered along the sides of abutting cells to prevent their separation o On the cytoplasmic face of each plasma membrane is a thickening called a plaque ▪ Adjacent cells are held together by thin linker protein filaments called cadherins that extend from the plaques and fit together like the teeth of a zipper in the intercellular space ▪ Thicker keratin filaments extend from the cytoplasmic side of the plaque across the width of the cell to anchor the plaque on the cells opposite side o Desmosomes are found in muscle cells • Gap Junctions – a gap junction is a communicating junction between adjacent cells. o At gap junctions the adjacent plasma membranes are very close, and hollow cylinders called connexons, which are composed of transmembrane proteins, connect the cells. o Ions, simple sugar, and other small molecules pass through these water- filled channels from one cell to the next. o Gap junctions are present in electrically excitable tissues where ion passage from cell to cell helps synchronize their electrical activity and contraction. CONTINUED...............DOWNLOAD FOR BEST SCORES [Show More]

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