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plasma membrane - zkadhem
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05-25-2007, 04:19 PM
12.
Which of the following is primarily responsible for the polyanionic charge on the outer surface of the plasma membrane? A.Cholesterol B.Glycoprotein C.Free saccharide groups D.Peripheral membrane protein E.Integrins
05-25-2007, 04:33 PM
The answer is: B
The carbohydrate of biological membranes is found in the form of glycoproteins and glycolipids rather than as free saccharide groups. The polyanionic charge of the membrane is produced by the sugar side chains on the glycoproteins and glycolipids. Glycoproteins often terminate in sialic acid side chains, which impart a negative (polyanionic) charge to the membrane. Similarly, the glycolipids (a/k/a glycosphingolipids), particularly the gangliosides, terminate in sialic acid residues with a strong negative charge. Cholesterol alters membrane fluidity. It is amphipathic (hydrophilic and hydrophobic properties). It acts by reducing the packing of lipid acyl groups through its steroid ring structure and hydrocarbon tail and cementing hydrophilic regions of the membrane through interactions with its hydroxyl (OH“) region. Peripheral membrane proteins are found on the cytosolic leaflet of the membrane bilayer. Integrins are heterodimeric receptors that bind with extracellular matrix (ECM) molecules such as laminin and fibronectin.
05-25-2007, 04:37 PM
brain teasing qs, I am having a migraine already with just one qs
 Thanks again |
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