BIOLOGY 172 Chapter 5.1-5.2: Lipids and Membranes

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7 Feb 2017
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Biology 172
Dr. Simmons Winter 2017
Reading 9/10: Chapter 5.1-5.2
Lipids are the main components of cell membranes
Cell membranes are composed of 2 layers of lipids
Major types of lipids
Phospholipids are made up of glycerol backbone attached to a phosphate group
(hydrophilic) and two fatty acids (hydrophobic)
Amphipathic molecules have both hydrophobic and hydrophilic regions
In aqueous environments, amphipathic molecules spontaneously arrange themselves so that
the polar heads are on the outside and are interacting with water while the nonpolar tails come
together on the inside
Shape of the phospholipid structure is determined by bulkiness of head group relative to tails
Micelles are spherical structures forming with bulky heads and 1 fatty acids
Bilayers are less bulky at the head and have 2 fatty acids; spontaneously form, as long as the
concentration of free phospholipids is high enough and pH of solution is similar to the pH of the
cell
Liposomes are enclosed bilayer structures spontaneously formed by phospholipids in neutral
pH environments
Lipids freely associate with one another due to extensive van der Waals forces
Membrane is said to be fluid because membrane lipids can move in the plane of membrane
Degree of fluidity depends on what types of lipids are in the bilayer
Longer tails, more VDW forces, tighter packing, less fluidity
Saturated Fats have no double bonds and are straight and tightly packed
Unsaturated Fats have double bonds, resulting in kinks in tails that enhance fluidity and
decrease tight packing
Cholesterol is another major component of animal cell membranes; it is amphipathic
Cholesterol typically increases or decreases membrane fluidity depending on the temperature
@ temperatures that are normally found in the cells, decrease in fluidity
@ temperatures that are lower, increase in fluidity
*Membranes are not always uniform; studded w/ discrete components
Proteins associate with membranes in different ways
Transporters move ions or other molecules across the membrane
Receptors allow cell to receive signals from environment
Enzymes catalyze chemical reactions
Anchors attach to other proteins to help maintain cell structure and shape
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