Lipids Flashcards
*biomolecules that contain fatty acids or a steroid nucleus
*soluble in organic solvents but not in water
*named for the Greek word lipos, which means “fat”
*extracted from cells using organic solvents
Lipids
Types of Lipis
waxes, fats and oils, glycerophospholipids. prostaglandins, steroid
Types of lipids that contain fatty acids
waxes, fats and oils, glycerophospholipids. prostaglandins
The type of lipids that do not contain fatty acids
Steroids
-are long-chain
carboxylic acids
-typically contain 12 to
18 carbon atoms
-are insoluble in water
-can be saturated or
unsaturated
Fatty acids
-single C—C bonds
-molecules that fit closely together
in a regular pattern
-strong attractions between fatty
acid chains
-high melting points that make
them solids at room temperature
Saturated fatty acids
what is these saturated fatty acids?
CH3-(CH2)14-COOH
Palmitic acid
-have one or more double C═C bond
-typically contain cis double bonds
Unsaturated fatty acids
What is this unsaturated fatty acid?
CH3-(CH2)7-CH=CH-(CH2)7-COOH
Oleic acid
-have “kinks” in the fatty
acid chains
-do not pack closely
-have fewer attractions
between chains
-have lower melting points
-are liquids at room
temperature
Unsaturated fatty acids
Give the two monounsaturated fatty acids
Palmitoleic acid and Oleic acid
-20 carbon atoms in their fatty acid chains
-an OH on carbons 11 and 15
-a trans double bond at carbon 13
Prostaglandins
-produced by injured tissues
-involved in pain, fever, and inflammation
-not produced when anti-inflammatory drugs such as aspirin inhibit their synthesis
Prostaglandins
in vegetable oils are mostly _________ with the first C═C at C6
CH3─(CH2)4─CH═CH─CH2─CH═CH─(CH2)7─COOH
Linoleic acid
omega-6
in fish oils are mostly ________with the first C═C at C3
CH3─CH2─(CH═CH─CH2)3─(CH2)6─COOH
Linolenic acid
omega-3
-esters of saturated fatty acids and long-chain alcohols
-coatings that prevent loss of water from leaves of plants
Waxes
-also called triacylglycerols
-esters of glycerol
-produced by esterification
-formed when the hydroxyl
groups of glycerol react with the
carboxyl groups of fatty acids
fats and oil
glycerol forms ester bonds with three fatty acids
triacylglycerol
Glycerol and three stearic acid molecules form a triacylglycerol named
glyceryl tristearate and tristearin
contains a high percentage of oleic
acid, which is a monounsaturated fatty
acid with one cis double bond
olive oil
-is solid at room temperature
-is prevalent in meats, whole milk, butter, and cheese
fat
-is liquid at room temperature
-is prevalent in plants such as olive and safflower
Oil
-have more unsaturated fats
-have cis double bonds that cause “kinks” in the fatty acid chains
-cannot pack triacylglycerol molecules as close
together as in fats
-have lower melting points than do saturated fats
-are liquids at room temperature
Oils
double bonds in unsaturated
fatty acids react with H2 in the presence of a Ni or Pt catalyst.
Hydrogenation
ester bonds are split by water in
the presence of an acid, a base, or an enzyme.
hydrolysis
-converts double bonds to single bonds
-adds hydrogen (H2) to the carbon atoms of double bonds
-increases the melting point
-produces solids such as margarine and shortening
Hydrogenation
-used in foods as an artificial fat
-sucrose linked by ester bonds to several long-chain fatty chains
-not broken down in the intestinal tract
Olestra
-are formed during hydrogenation when cis double bonds are converted to trans double bonds
-in the body behave like saturated fatty acids
-are estimated to make up 2 to 4% of our total
calories
-in several studies are reported to raise
LDL-cholesterol and lower HDL-cholesterol
Trans fatty acids
-the unsaturated fats usually contain cis double
bonds
-during hydrogenation, some cis double bonds are converted to trans double bonds (more stable), causing a change in the fatty acid structure
-a label states “partially” or “fully hydrogenated” if the fats contain trans fatty acids
Vegetable oils
There are more unsaturated fats in vegetable oils. TRUE OR FALSE
TRUE
Vegetable oils have higher melting points than
fats. TRUE OR FALSE
FALSE
Hydrogenation of oils converts some cis-double
bonds to trans-double bonds. TRUE OR FALSE
TRUE
Animal fats have more saturated fats. TRUE OR FALSE
TRUE
-water adds to the ester bonds
-triacylglycerols split into glycerol and three fatty acids
-an acid or enzyme catalyst is required
acid or enzyme hydrolysis
-a triacylglycerol reacts with a strong base
-a triacylglycerol splits into glycerol and the salts of fatty acids
-soaps (salts of fatty acids) form
Base hydrolysis (saponification)
What products are obtained from the complete
hydrolysis of glyceryl trioleate?
Glycerol and 3 oleic acids
-the most abundant lipids in
cell membranes
-composed of glycerol, two
fatty acids, phosphate,
and an amino alcohol
Glycerophospholipids
-two nonpolar fatty acid chains
-a phosphate group
-one of three polar amino alcohols
Glycerophospholipids
-are abundant in brain and nerve tissues
-are found in egg yolk, wheat germ, and yeast
-contain choline (in_____ ) or either ethanolamine or
serine (in _______)
lecithin, cephalins
is an 18-carbon unsaturated amino alcohol.
Sphingosine
the NH2 group in
sphingosine is
attached by an amide
bond to a fatty acid
ceramide
-are similar to glycerophospholipids
-contain sphingosine, a fatty acid, phosphate, and an amino alcohol
Sphingolipids
-is a sphingolipid found in nerve cells
-bonds the —OH of a ceramide to a phosphate ester of choline
Sphingomyelin
sphingolipids that contain monosaccharides attached by a β-glycosidic bond to the —OH group of ceramide
Glycosphingolipids
-contain galactose or glucose attached by a
β-glycosidic bond to the —OH group of ceramide
-are found in the brain and the myelin sheath
-are important in cellular recognition and tissue
immunity
Cerebrosides
are sphingolipids that contain chains of two to seven monosaccharides
-are important in neurons
-are found on cell membrane surfaces
-act as receptors for hormones, viruses, and drugs
-can cause genetic diseases if they accumulate
-that accumulates in Tay-Sachs disease when
hexoamidase A is defective
Gangliosides
-has 3 cyclohexane rings
-has 1 cyclopentane ring
-contains no fatty acids
-has four rings A, B, C, and D
-is numbered from the carbon
atoms in ring A to two methyl
groups at 18 and 19
Steroid nucleus
-is the most abundant steroid in the body
-has methyl CH3-groups, an alkyl chain, and
—OH attached to the steroid nucleus
Cholesterol
-are synthesized in the liver from cholesterol
-are stored in the gallbladder
-are secreted into the small intestine
-Have a polar and a nonpolar region
-mix with fats to break them part
-emulsify fat particles to provide large surface area
Bile salts
-combine lipids with proteins and phospholipids
-are soluble in water because the surface consists of polar lipids
Lipoproteins
Types of Lipids
triacylglycerol, phospholipids, cholesterol, cholesteryl esters, protein
-are chemical messengers in cells
-are produced from cholesterol
-include sex hormones such as androgens
(testosterone) in males and estrogens (estradiol) in females
Steroid hormones
-are produced by the adrenal glands located on the top of each kidney
-include aldosterone, which regulates electrolytes and water balance by the kidneys
-include cortisone, a glucocorticoid, which
increases blood glucose level and stimulates the synthesis of glycogen in the liver
Adrenal corticosteroids
-are derivatives of testosterone
-are used illegally to increase muscle mass
-have side effects that include fluid retention, hair growth, sleep disturbance, and liver damage
Anabolic steroids
-separate cellular contents from the external
environment
-consist of a lipid bilayer made of two rows of
phospholipids
-have an inner portion made of the nonpolar tails of phospholipids with the polar heads at the outer and inner surfaces
Cell membranes
-contains proteins, carbohydrates, and cholesterol
-has unsaturated fatty acids that make cell
membranes fluid-like rather than rigid
-has proteins and carbohydrates on the surface that communicate with hormones and neurotransmitters
Lipid bilayer
which moves particles from a higher to a lower concentration
Diffusion (passive transport)
Which uses protein channels to increase the rate of diffusion
Facilitated transport
which moves ions against a concentration gradient
Active transport
The transport of particles across a cell membrane from high concentration to low concentration is called
Diffusion (passive transport)
are of great importance to the body as the chief concentrated storage
form of energy, besides their role in cellular structure and various other biochemical functions.
Lipids
What are the classification of lipids
- Simple lipids
- complex (compound) lipids
- Derived lipids
- Miscellaneous lipids
- Neutral lipids
These are esters of fatty acids with glycerol. The difference between fat and oil is only physical. Thus, oil is a liquid while fat is a solid at room temperature.
Fats and oils (triacylglycerols)
Esters of fatty acids (usually long chain) with alcohols other than glycerol. These
alcohols may be aliphatic or alicyclic. Cetyl alcohol is most commonly found in waxes.
Waxes
used in the preparation of candles, lubricants, cosmetics, ointments, polishes etc.
Waxes
They contain phosphoric acid and frequently a nitrogenous base. This is in
addition to alcohol and fatty acids.
Phospholipids
These are esters of fatty acids with alcohols containing additional groups
such as phosphate, nitrogenous base, carbohydrate, protein etc. They are further divided as follows
Complex (compound) lipids
These phospholipids contain glycerol as the alcohol e.g., lecithin, cephalin.
Glycerophospholipids
Sphingosine is the alcohol in this group of phospholipids e.g., sphingomyelin.
Sphingophospholipids
These lipids contain a fatty acid, carbohydrate and nitrogenous base. The alcohol
is sphingosine; hence they are also called as glycosphingolipids. Glycerol and phosphate are
absent e.g., cerebrosides, gangliosides.
Glycolipids
Macromolecular complexes of lipids with proteins.
Lipoproteins
These are the derivatives obtained on the hydrolysis of group 1 and group 2 lipids which
possess the characteristics of lipids. These include glycerol and other alcohols, fatty acids, mono- and diacylglycerols, lipid (fat) soluble vitamins, steroid hormones, hydrocarbons and ketone bodies.
Derived lipids
These include a large number of compounds possessing the characteristics of lipids
e.g., carotenoids, squalene, hydrocarbons such as pentacosane (in bees wax), terpenes etc.
Miscellaneous lipids
The lipids which are uncharged are referred to as neutral lipids. These are mono-, di-,
and triacylglycerols, cholesterol and cholesteryl esters.
Neutral lipids
are carboxylic acids with hydrocarbon side chain. They are the simplest form of lipids.
Fatty acids
fatty acids that do not contain double bonds,
Saturated fatty acids
fatty acids that contain one or more
double bonds.
Unsaturated fatty acids
Fatty acids with one double bond are
Monounsaturated fatty acid
those with 2 or more double bonds are collectively known as
Polyunsaturated fatty acids
The saturated fatty acids end with a suffix
-anoic
unsaturated fatty acids end
with a suffix
-enoic
The terminal carbon
containing methyl group is known
omega (ɯ) carbon
how much carbon does the short chain has?
less than 6 carbons
how much carbon does the medium chain has?
8 to 14 carbons
how much carbon does the long chain have?
16 to 24 carbons
The fatty acids that cannot be synthesized by the body and, therefore, should be supplied in the diet are known as essential fatty acids (EFA). Chemically, they are
are polyunsaturated fatty acids, namely linoleic
acid (18: 2; 9, 12) and linolenic acid (18: 3; 9, 12, 15). Arachidonic acid (20: 4; 5, 8, 11, 14)
The deficiency of EFA results in
phrynoderma or toad skin
If the atoms or acyl groups are present on the same side of the double bond, it is a
cis configuration
if the groups occur on the opposite side, it is a
trans configuration
Some of the fatty acids are hydroxylated. E-Hydroxybutyric acid, one of the ketone
bodies produced in metabolism, is a simple example of hydroxy fatty acids. Cerebronic acid and recinoleic acid are long chain hydroxy fatty acids.
Hydroxy fatty acids
Fatty acids with cyclic structures are rather rare e.g., chaulmoogric acid found in
chaulmoogra oil (used in leprosy treatment) contains cyclopentenyl ring.
Cyclic fatty acids
These compounds are related to eicosapolyenoic fatty acids and include prostaglandins, prostacyclins, leukotrienes and thromboxanes. They are discussed together.
Eicosanoids
Triacylglycerols are the most abundant group of lipids that primarily function as fuel
reserves of animals. The fat reserve of normal humans (men 20%, women 25% by weight) is sufficient to meet the body’s caloric requirements for 2-3 months.
Fats as stored fuel
Adipocytes of adipose tissue—predominantly found in th subcutaneous layer and in the abdominal cavity—are specialized for storage of triacylglycerols. The fat is
stored in the form of globules dispersed in the entire cytoplasm. And surprisingly, triacylglycerols are not
the structural components of biological membranes.
Fats primarily occur in adipose tissue
Monoacylglycerols, diacylglycerols and triacylglycerols, respectively
consisting of one, two and three molecules of fatty acids esterified to a molecule of glycerol, are known. Among these, triacylglycerols are the most important biochemically.
Structures of acyglycerols
Triacylglycerols undergo stepwise enzymatic hydrolysis to finally liberate free fatty acids
and glycerol. The process of hydrolysis, catalyzed by lipases is important for digestion of fat in the gastrointestinal tract and fat mobilization from the adipose tissues.
Hydrolysis
The hydrolysis of triacylglycerols by alkali to produce glycerol and soaps is known as
saponification. Triacylglycerol + 3 NaOH or Glycerol + 3 R-COONa (soaps)
Saponification
Rancidity is the term used to represent the deterioration of fats and oils resulting in an
unpleasant taste. Fats containing unsaturated fatty acids are more susceptible to rancidity.
Rancidity
occurs due to partial hydrolysis of triacylglycerols by bacterial enzymes. Oxidative
rancidity is due to oxidation of unsaturated fatty acids. This results in the formation of unpleasant products such as dicarboxylic acids, aldehydes, ketones etc. Rancid fats and oils are unsuitable for human consumption.
Hydrolytic rancidity
The substances which can prevent the occurrence of oxidative rancidity are known as
antioxidants. Trace amounts of antioxidants such as tocopherols (vitamin E), hydroquinone, gallic acid and D-naphthol are added to the commercial preparations of fats and oils to prevent rancidity. Propyl gallate,
butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) are the antioxidants used in food preservation.
Antioxidants
In the living cells, lipids undergo oxidation to produce peroxides and free
radicals which can damage the tissue. The free radicals are believed to cause inflammatory diseases, aging, cancer, atherosclerosis etc. It is fortunate that the cells possess antioxidants such as vitamin E, urate and superoxide dismutase to prevent in vivo lipid peroxidation.
Lipid peroxidatio in vivo
It is defined as the grams (number) of iodine absorbed by 100 g of fat or oil.
Iodine number
It is defined as the mg (number) of KOH required to hydrolyze (saponify) one
gram of fat or oil.
Saponification number
It is defined as the number of ml 0.1 N KOH required to completely
neutralize the soluble volatile fatty acids distilled from 5 g fat.
Reichert-Meissl (RM) number
It is defined as the number of mg of KOH required to completely neutralize free fatty acids present in one gram fat or oil.
Acid number
are the major lipids that occur in biological membranes. They consist of glycerol 3-
phosphate esterified at its C1 and C2 with fatty acids. Usually, C1 contains a saturated fatty acid while C2
contains an unsaturated fatty acid.
Glycerophospholipids
-This is the simplest phospholipid. It does not occur in good concentration in the
tissues.
-is an intermediate in the synthesis of triacylglycerols and
phospholipids.
Phosphatidic acid
These are the most abundant group of phospholipids in the cell
membranes. Chemically, lecithin (Greek: lecithos—egg yolk) is a phosphatidic acid with choline as the base.
Lecithins
