LIPIDS Flashcards
- a family of substances that are insoluble in water but soluble in nonpolar solvents and solvents of low polarities, such as diethyl ether.
- They are not defined by functional groups, thus they have a variety of structures and functions.
- They contain many nonpolar C—C and C—H bonds and few polar bonds resulting in their water insolubility.
- found in biological systems are either hydrophobic or amphipathic.
Lipid
- a heterogeneous group of compounds that are related more by their physical than by their chemical properties.
- They are relatively insoluble in water and soluble in a non-polar solvent.
- It is greasy to touch and leaves a permanent oily stain on the paper.
- lighter than water
- poor conductors of heat and electricity and therefore serve as excellent insulators for the body, slowing the loss of heat through the skin.
Lipids
Are colorless with bland odor and taste. When heated strongly, undergoes decomposition forming acrid flammable vapors and when ignited, they burn with a sooty flame.
Pure lipids
a major source of energy for the body, and they also provide the hydrophobic barrier that permits the partitioning of the aqueous contents of cells and subcellular structures.
Lipids
also act as precursors for other lipids and play a role in the transport of other lipids in the body. They also function as emulsifying agents in the gastrointestinal tract.
lipids
Deficiencies or imbalances of lipid metabolism
can lead to some of the major clinical problems encountered by physicians, such as atherosclerosis and obesity.
REACTIONS OF LIPIDS
HYDROLYSIS
HYDROGENATION
OXIDATION
Fats and oils can be hydrolyzed in the presence of an acid, a base, or specific enzymes known as lipases.
Hydrolysis
The hydrolysis of fats and oils in the presence of a base is used to make soap and is called
saponification.
Acid, base, or specific enzymes used to hydrolyze fats and oils are called
lipases
Fats and oils that are in contact with moist air at room temperature eventually undergo oxidation and hydrolysis reactions that cause them to turn rancid, acquiring a characteristic disagreeable odor
Oxidation
The double bonds in fats and oils can undergo ____.
Chemically, it is essentially identical to the catalytic hydrogenation reaction described for alkenes.
Hydrogenation
CATEGORIES OF LIPIDS
HYDROLYZABLE
NONHYDROLYZABLE
can be converted into
smaller molecules by hydrolysis.
Hydrolyzable lipids
Cannot be cleaved into
smaller molecules by aqueous hydrolysis.
Nonhydrolyzable lipids
Hydrolyzable lipids are derived from ______
fatty acids
carboxylic acids (RCOOH) with
long C chains of 12-20 C atoms.
have an even
number of C atoms.
Fatty acids
have no double bonds
in their long hydrocarbon chains.
Saturated fatty acids
have 1 or more double
bonds (generally cis) in their long hydrocarbon
chains.
Unsaturated fatty acids
are essential fatty
acids; they cannot be produced by the body
and must be consumed.
Linoleic and linolenic acids
called an omega-6 acid, because
of the position of the first C=C in the nonpolar chain.
Linoleic acid
called an omega-3 acid, because
of the position of the first C=C in the nonpolar chain.
Linolenic acid
- esters formed from a fatty acid and a
high molecular weight alcohol. - hydrophobic due to long nonpolar C chains
- They form protective coatings on bird’s feathers
and sheep’s wool and make up beeswax. - hydrolyzed with water
in the presence of acid or base to re-form the
carboxylic acid and alcohol they came from.
Waxes
three esters
formed from glycerol and three molecules of
fatty acids.
Triacylglycerols (triglycerides)
Triacylglycerols that have three identical fatty
acid side chains
Simple triacylglycerols
Triacylglycerols that have two or three different
fatty acids.
Mixed triacylglycerols
Triacylglycerols that contain only saturated
fatty acids; they make up most animal fat and are
solids at room temperature.
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Saturated triacylglycerols
triacylglycerols that contain at least one
unsaturated fatty acid; they make up most
vegetable oils and are liquids at room temperature.
Unsaturated triacylglycerols
triacylglycerols that have 1 C=C bond.
Monounsaturated triacylglycerols
triacylglycerols have many C=C
bonds.
Polyunsaturated triacylglycerols
________ the number of double bonds in the
fatty acid chain __________ the melting point of the
triacylglycerol.
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Increasing
decreases
- have higher melting points; they are solids
at room temperature. - are derived from fatty acids with few double
bonds.
Fats
- have lower melting points; they are liquids
at room temperature. - are derived from fatty acids having a larger
number of double bonds.
Oils
used to build cell membranes, insulate
the body, and store energy for later use.
fats
It is recommended that no more than _____% of a
person’s caloric intake should come from lipids
20-35%
A high intake of ________________ is
linked to heart disease
saturated triacylglycerols
stimulate cholesterol synthesis,
which can lead to cholesterol plaques building up
inside arteries.
Saturated fats
lower the risk of
heart disease by decreasing the level of cholesterol
in the blood.
Unsaturated triacylglycerols
are
very helpful in lowering the risk of heart attack.
Triglycerols formed from omega-3 fatty acids
if the double bond of the unsaturated
triacylglycerol is ____, the beneficial effect is lost.
trans
which are primarily synthesized
instead of naturally occurring, act like saturated
fats and increase the cholesterol levels in the blood.
Trans fats
Triacylglycerols are hydrolyzed with water in the
presence of ____,____, or _____ in the body
acid, base, or enzymes
Humans store energy as ________ in
adipose cells below the surface of the skin, in the
breast area, and surrounding internal organs.
triacylglycerols
To metabolize triacylglycerols for energy, the esters
are hydrolyzed by enzymes called ______
lipases
metal salts of fatty acids prepared by
basic hydrolysis (saponification) of a triacyl-
glycerol.
polar head
ionic end
nonpolar tail
nonpolar end 27
Soaps
dissolve grease and oil and
the polar head makes it soluble in water.
nonpolar tails
made from lard (from hogs), tallow
(from cows or sheep), coconut oil, or palm oil
Soaps
lipids that contain a P atom.
Phospholipids
Two common types of phospholipids
phosphoacylglycerols and sphingomyelins.
- the main component
of most cell membranes. - Structurally, they resemble a triacylglycerol, except
the third fatty acid has been replaced with
a phosphodiester bonded to an alcohol - main types are cephalin, lecithin
Phosphoacylglycerols
- do not contain a glycerol
backbone, they have a sphingosine backbone
instead.
-do not contain an ester; their
single fatty acid is bonded to the backbone by
an amide bond.
sphingosine
Sphingomyelins
the coating that surrounds
nerve cells, is rich in sphingomyelins.
myelin sheath
- surrounds the cytoplasm, the
aqueous medium inside the cell. - acts as a barrier to stop the
passage of ions and molecules into or out of the
cell. - selectively
permeable.
cell membrane
the major component of cell
membranes, contain a hydrophilic polar head and
two hydrophobic nonpolar tails.
Phospholipids
When phospholipids
are mixed with water,
they assemble in a
lipid bilayer
are embedded
in the lipid bilayer membrane. (structure of cell membrane)
Proteins and cholesterol molecules