BLG 143 Study Guide - Final Guide: Alkane, Lipid Bilayer, Close-Packing Of Equal Spheres
6.2 Phospholipid Bilayers
Micelles tiny droplets created when the hydrophilic heads face the water and the
hydrophobic tails are forced together, away from the water
Phospholipid bilayers
• created when 2 sheets of phospholipid molecules align
• hydrophilic heads in each layer face a surrounding solution
• hydrophobic tails face one another inside the bilayer
• form spontaneously, no input of energy
• tend to form from phospholipids with longer tails
Selective Permeability of Lipid Bilayers
Permeability structure’s tendency to allow a given substance to pass across it
Lipid bilayers are highly selective.
Selective permeability some substance cross a membrane more easily than others
➢ small nonpolar molecules move across bilayers quickly
➢ small polar molecules cross relatively rapidly
➢ charged/large polar substances cross slowly, if at all get help from membrane
proteins
Lipid Structure Affects Membrane Permeability
Saturated hydrocarbons without double bond (saturated with maximum number of H
atoms that can attach to the carbon skeleton)
Unsaturated hydrocarbons at least one double bond
When hydrophobic tails are packed into a lipid bilayer, the kinks created by double bonds
produce spaces among the tightly packed tails. These spaces reduce the strength of
hydrophobic interactions between the tails. These interactions are stronger among
saturated hydrocarbon tails.
Hydrophobic interactions become stronger as saturated hydrocarbon tails increase in
length.
Double bonds between carbons in a hydrocarbon chain can cause a kink.
➢ Prevents close packing of hydrocarbon tails
➢ Reduces hydrophobic interactions much more permeable
Short, unsaturated double bonds C-H tails allow more material to pass through membrane.
Interior is held together less tightly, due to kinks.
Highly saturated fats like butter are solid at room temperature.
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Document Summary
Micelles tiny droplets created when the hydrophilic heads face the water and the hydrophobic tails are forced together, away from the water. Permeability structure"s tendency to allow a given substance to pass across it. Selective permeability some substance cross a membrane more easily than others. Small nonpolar molecules move across bilayers quickly. Charged/large polar substances cross slowly, if at all get help from membrane proteins. Saturated hydrocarbons without double bond (saturated with maximum number of h atoms that can attach to the carbon skeleton) Unsaturated hydrocarbons at least one double bond. When hydrophobic tails are packed into a lipid bilayer, the kinks created by double bonds produce spaces among the tightly packed tails. These spaces reduce the strength of hydrophobic interactions between the tails. These interactions are stronger among saturated hydrocarbon tails. Hydrophobic interactions become stronger as saturated hydrocarbon tails increase in length. Double bonds between carbons in a hydrocarbon chain can cause a kink.