BIOB10H3 Lecture : Important Terms and Definitions

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LECTURE#5
x A function of the plasma membrane is that it serves as a scaffold fro biochemical activities eg.
signalling proteins send signals to the nucleus
x It allows the cell to respond to extracellular signals eg. signals could tell cels to prepare for cell
division ; cell surface receptors that bind ligand on the cell exterior can send signals into the
cytoplasm of the cell
x PM is a lipid bilayer
x Hydrophobic interactions of the fatty acid tails of the PM
x Protein channels within the bilayer
x Short sugar chains on proteins and lipids are called glycoproteins or glycolipids
x Membrane lipids are amphipathic, contain both hydrophobic and hydrophilic regions; 3tyes
o Phospholipids
o Sphingolipids
o Cholesterol
x Sphingolipids are composed of an amino alcohol with a long hydrocarbon chian called
sphingosine and a single fatty acid chain; fatty acid is attached to the amino group of
sphingosine; ceramide is the simplest sphingolipid
x Glycolipids are formed when a sugar is attached to the terminal alcohol of a sphingosine; certain
viruses and txins eg. cholera/influenza toxins bind to cell surface glycoproteins and gain access
to cells
x 3 types of membrane proteins
o Integral membrane proteins: transmembrane proteins (expand bilayer)
Are single or multipass; can pass through membrane once or several times
CFTP is defective in cystic fibrosis patiens (ccystic fibrosis transmembrane
proteins)
o Peripheral membrane proteins: on cytoplasmic or extracellular side of PM
Often transiently interact with PM eg. response to signals
o Lipid-anchored proteins: can be on cytoplasmic or extracellular side (anchored on wither
side)
On the extracellular side, proteins are attached to a complex oligosaccharide
linked to a phosphatidylinotisol t form GPI glycophosphatidylinisol linked
proteins eg. some receptors such as prion
x Membrane fluidity depends on:
o Temperature
o The types of lipids
o The presence of cholesterol tdisrupts the packing of fatty acid chain
x Transition temperature = the greater the degree of unsaturation, the lower the temperature
beore the bilayer gels; eg. butter gels at higher temp than oil; more trans fats in oil than butter
x Various factors influence the mobility of integral membrane proteins
o Local crowding of proteins; neighbours restrict movement
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