Membranes

• Membranes define the external boundary of the cells and regulate the molecular traffic across that boundary
• Membranes divide the internal space into discrete compartments to segregate processes and components
• Membranes facilitate cell to cell communication
• The physical properties of membranes is that they are flexible, self sealing and are selectively permeable to polar solutes
• Membrane structure composes of a protein, lipid, and carbohydrate which varies among any cell types and organelles
• Membrane lipids are amphipatic molecules
• Archaeal membranes are different from eukaryotic or bacterial membrane
• The fatty acids are joined to the glycerol backbone by an ether linkage, and the alkyl side chain are branched
• Archaeals survive in harsh conditions
• The micellar structure formed depends on the size of the nonpolar tail and its numbers
• As the number increases, the core of the micellar structure also increases
• The wall of liposome consists of a lipid bilayer
• The lipid bilayer is a fluid mixture with a thickness of between 30 to 40 Angstrom with a hydrophobic core of about 25 to 30 A thick
• Non polar tails constantly moves
• The longer the chain, the more solid and saturated it will be, and the more liquid and unsaturated
• The hydrophobic tails in the lipid bilayer are in constant motion due to the rotation around the C=C bond of the tail or kinking
• The rotation of the lipid head group is limited because of interactions between polar or charged head groups
• Changes in the polar heads can result in imbalances in the pressure profile, which can interfere with the stability and morphology of the lipid bilayer.
• The lower the temperature, a phase change implies in the lipid bilayer thus loses its fludity and becomes solid like
• The fluidity of the lipid bilayer is dependent on the temperature, fatty acid and cholesterol content
• The higher the number of carbons, the higher the melting point
• The lower the number of carbons, the lower the melting point
• The higher the degree of unsaturation, the lower the melting point
• Cholesterol reduces membrane fluidity
• Increasing the amount of saturated fatty acids increases the rigidity of the cell membrane
• The rigid ring systems in cholesterol when attached to a lipid bilayer interferes with the motion of the fatty acid side chains in other membrane lipids
• The presence of cholesterol stabilizes the extended chain conformations of hydrocarbon tails of FA
• The plant membranes have a higher percentage of unsaturated fatty acids than animal membranes
• The presence of cholesterol favors animal membranes
• The membranes of prokaryotes which does not contain any steroids are the most fluid
• Transverse diffusion or flip flop flips polar head to the other side and it is very slow because it must be flipped and undergo to a nonpolar environment
• Lateral diffusion refers to the diffusion within the layer
• Membrane proteins known as flippases catalyze the flip-flop of specific phospholipids