Biology Chapter 5: Lipids

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- the one class of biological molecules that does not include/form true polymers- generally not big enough to be considered macromolecules- grouped together because they share one important trait: they mix poorly, if at all, with water- thus are hydrophobic
the hydrophobic behavior of lipids is based on what?
their molecular structure
other characteristics of lipids include what?
- consist mostly of hydrocarbon regions- varied in form and function- include waxes and certain pigments- also fats, phospholipids and steroids
- not smaller molecules, large molecules assembled from smaller molecules by dehydration reactions- constructed from two kinds of smaller molecules: glycerol and fatty acids
a 3 carbon alcohol with a hydroxyl group attached to each carbon
fatty acids
- a fatty acid has a carboxy attached to a carbon skeleton- contain a long carbon skeleton, usually 16 to 18 carbon atoms in length

the carbon at the end of a fatty acid's carbon skeleton is part of what?
a carboxyl group which is the functional group that gives the molecules the name fatty acid
the rest of the carbon skeleton is composed of what?
hydrocarbon chain
what is the reason why fats are hydrophobic?
- the relatively non polar C--H bonds in the hydrocarbon chains of fatty acids- fats separate from water because the water molecules hydrogen bond to one another and exclude fats
in making fat, how many fatty acid molecules are each joined to glycerol by an ester linkage?
- three- a bond b/w a hydroxyl group and a carboxyl group
- resulting fat of a bond b/w a hydroxyl group and a carboxyl group- consist of 3 fatty acids linked to one glycerol molecule
what are the similarities and differences in the fatty acids in a fat?
- they can be the same - or they can be two or three different kinds
saturated and unsaturated fats
terms refer to the structure of the hydrocarbon chains in the fatty acids
saturated fatty acid
- if there are no double bonds between carbon atoms composing in a chain, then as many hydrogen atoms as possible are bonded to the carbon skeleton- and is said to be saturated with hydrogen
unsaturated fatty acid
- has one or more double bonds- with one fewer hydrogen atom on each double-bonded carbon- nearly all double bonds in naturally occurring fatty acids are cis double bonds, which cause a kink in the hydrocarbon chain wherever they occur
most animals fats are saturated or unsaturated?
- saturated- the hydrocarbon chains of their fatty acids, the "tails" of the fat molecules, lack double bonds, and their flexibility allows the fat molecules to pack together tightly

saturated (animal) fats
- solid at room temperature- include lard and butter
unsaturated (plant and fish) fats
- liquid at room temperature- built of one or more unsaturated fatty acids- referred to as oils ( such as olive oil)- the kinks where the cis double bonds are located prevent the molecules from packing together closely enough to solidify at room temperature
trans fats
- may contribute more than saturated fats atherosclerosis- especially common in baked goods and processed foods
unsaturated fatty acids must be supplied in the human body because?
- they cannot be synthesized in the body- include omega-3 fatty acids, which are required for normal growth in children and protect against cardiovascular decease in adults
what is the major function of fats?
- energy storage- the hydrocarbon chains in fat are similar to gasoline molecules and just as rich in energy- the energy is in the bond
- two fatty acids and a phosphate- the two fatty acids are hydrophobic, the phosphate is hydrophilic- without it cells could not exist- essential for cells because they make up cell membranes - when phospholipids are added to water, they self- assemble into double-layered structures called "bilayers" shielding their hydrophobic portions from water - at the surface of a cell, phospholipids are arranged in a similar bilayer - the phospholipid bilayer form a boundary between the cell and its external environment and allow cells to exist
the structure of a phospholipid is based on what?
differences in the two fatty acids and in the groups attached to the phosphate group of the head

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