lipids
DESCRIPTION
Lipids. What are Lipids? . Lipids are non-polar (hydrophobic) organic compounds, insoluble in water, soluble in organic solvents (ether, acetone, carbontetrachloride ). They contain carbon, hydrogen, and oxygen; sometimes nitrogen and phosphorus. - PowerPoint PPT PresentationTRANSCRIPT
Lipids
Lipids are non-polar (hydrophobic) organic compounds, insoluble in water, soluble in organic solvents (ether, acetone, carbontetrachloride). They contain carbon, hydrogen, and oxygen; sometimes nitrogen and phosphorus. In most cases they yield fatty acids on hydrolysis.They take place in lipid and plant metabolism.
What are Lipids?
Fatty acids
Fatty acids (FAs) consist of hydrocarbon chain with a carboxylic acid at one end straight-chain organic acids Most naturally occurring fatty acids have an even number of carbon atoms
They can be saturated and unsaturated.
Unsaturated fatty acids have lower melting points than saturated fatty acid.
Fatty acids
Monounsaturated FAs one double bond
Polyunsaturated FAs many double bonds
Eicosanoids (include prostaglandins, leukotriens, prostacyclins, thromboxanes)Double bonds in fatty acids are usually
in the cis configuration.
Linoleic acid is a nutritionally essential fatty acid. that must be ingested by humans and other animals because the body requires it but cannot synthesize it.
It is found in large conc. in corn, peanut, soyabean oils but not in olive oil.
Absence of linoleic acid by infants weight loss and ezema.
Linoleic acid
Classification of lipids according to their structures
Classification of lipids according to their structuresSimple lipids esters of FAs (FAT, OIL, WAX) [One or two chemical identities)
Hydrolysis of a simple lipid Simple lipid + H2Ofatty acid + alcohol
If the alcohol is glycerol (FAT or OIL)
If the alcohol is a monohydric alcohol WAX
Hydrolysis of complex lipids more fatty acids + alcohol +other compound
Phospholipid + H2O (hydrolysis) FA + alcohol + phosphorus + nitrogen compound.
Phospholipids phosphoglyceride or phosphosphingoside
Glycolipid + H2O (hydrolysis) FA +a carbohydrate + sphingosine
Precursor lipids compounds resulting from hydrolysis of simple or complex lipids (FA, sphingosine)
Derived lipids lipids which are formed due to the transformation of fatty acids (Prostaglandins, Fat-soluble vitamins)
Classification of lipids according to their structures
Fats and oilsFats with a melting point below room temperature are called oils.
Iodine numberThe iodine number of a fat or an oil is the umber of grams of iodine that will react with the double bond present in 100 g of fat or oil
Higher iodine number higher degree of unsaturation
Generally iodine number of animal fats < iodine number of vegetable oils
Iodine number of fats <70
Iodine number of oils > 70
Some uses of lipids in the body Fats serve as fuel.
Fats serve as reserve supply of food and energy.
Fats are stored in special adipose tissues and serve as a protector for vital organs.
Fats act as heat insulators.
Some lipids allow rapid propagation of electrical signals.
Physical properties White or yellowish solid or liquids
Pure fats and oils are odorless and tasteless. Over a period of time they become rancid and develop an unpleasant odor and tatse.
Lighter than water.
When shaken with water temporarily emulsion.
Emulsion can made permanent by addition of emulsifying agent such soap.
Fats and oils must be emulsified before they can be digested.
Chemical reactionsHydrolysis
3. Enzyme
Saponification
Hydrogenation
In Practice not all double bonds are hydrogenated.Hydrogenation lowers the iodine number.
Acrolein test: Test for fats or oils which contain glycerol
Glycerol (KHSO4) (heat)Acrolein (strong odor)
Rancidity: unpleasant odor or taste developed when fats stand at room temperature for a short period of time.Rancidity is due to hydrolysis and oxidation reactions.Oxidation of double bonds short chain aldehydes and acids bad odor and taste (Antioxidant Vit. E and C.)Fats + Water in butter (in presence of microorganisms)hydrolysis of fats Butyric acid disagreeable odor.Fats and foods containing fats have to be covered and stored in the refrigerator
Cleansing action of soaps
CH3-(CH2)16-COONa (Sodium stearate)
Non-Polar Polar
Hydrophopic Hydrophilic
Micelle
Mechanical Washing causes the oil to break down into small dropsSoap emulsifies then the oil and prevents it from coalescing.Soap acts also as surfactant lowers surface tension
Detergents
Synthetic compounds used as cleansing agents.
Soaps do not work in hard water insoluble Ca and Mg salts
Detergents work also in hard water
Soaps (alkaline); Detergents (neutral) Detergents can be used on silks and wool; Sops not.
Detergents: Sodium salts if long chain alcohol sulfates
Example: Sodium laurylsulfate
C12H23OH + H2SO4 C11H23CH2OSO3H + H2O
C11H23CH2OSO3H + NaOH C11H23CH2OSO3Na + H2O
Complex lipids and cell Membranes: an overview
Some functions of membranes (40-50% lipids; 50-60% Proteins)1. Mechanical support.2. Seperate contents of the cells from the environment3. Structural support for proteins (pumps; receptors)
Biochemistry IISelf aggregation of lipids
Introduction to lipids
Polar end (hydrophilic end)
non-polar endhydrophobic end)
Glycerophospholipids
Glycerophospholipids (phosphoglycerides), are common constituents of cellular membranes.They have a glycerol backbone.Hydroxyls at C1 & C2 are esterified to fatty acids.
C OHH
CH2OH
CH2OH
glycerol
An ester forms when a hydroxyl reacts with a carboxylic acid, with loss of H2O.
Formation of an ester:
O O
R'OH + HO-C-R" R'-O-C-R'' + H2O
Phosphatidate
In phosphatidate: fatty acids are esterified to hydroxyls on C1 & C2 the C3 hydroxyl is esterified to Pi.
O P O
O
O
H2C
CH
H2C
OCR1
O O C
O
R2
phosphatidate
In most glycerophospholipids (phosphoglycerides), Pi is in turn esterified to OH of a polar head group (X): e.g., serine, choline, ethanolamine, glycerol, or inositol. The 2 fatty acids tend to be non-identical. They may differ in length and/or the presence/absence of double bonds.
O P O
O
O
H2C
CH
H2C
OCR1
O O C
O
R2
X
glycerophospholipid
Phosphatidylinositol, with inositol as polar head group, is one glycerophospholipid. In addition to being a membrane lipid, phosphatidylinositol has roles in cell signaling.
O P
O
O
H2C
CH
H2C
OCR1
O O C
O
R2
OH
H
OH
H
H
OHH
OH
H
O
H OH
phosphatidyl- inositol
Phosphatidylcholine, with choline as polar head group, is another glycerophospholipid.
It is a common membrane lipid.
O P O
O
O
H 2 C
C H
H 2 C
OCR 1
O O C
O
R 2
C H 2 C H 2 N C H 3
C H 3
C H 3
+
p h o sp h a tid y lc h o lin e
O P O
O
O
H2C
CH
H2C
OCR1
O O C
O
R2
X
glycerophospholipid
Each glycerophospholipidincludes a polar region:
glycerol, carbonyl O of fatty acids, Pi, & the polar head group (X)
non-polar hydrocarbon tails of fatty acids (R1, R2).
Structure of phospholipids
Sphingosine may be reversibly phosphorylated to produce the signal molecule sphingosine-1-phosphate. Other derivatives of sphingosine are commonly found as constituents of biological membranes.
H2CHC
OH
CH
N+ CH
C
CH2
CH3
H
H3
OH
( )12
sphingosine
Sphingolipids are derivatives of the lipid sphingosine, which has a long hydrocarbon tail, and a polar domain that includes an amino group.
sphingosine-1-P
H2CHC
O
CH
N+ CH
C
CH2
CH3
H
H3
OH
( )12
P O
O
O
In the more complex sphingolipids, a polar “head group" is connected to the terminal hydroxyl of the sphingosine moiety of the ceramide.
H2CHC
OH
CH
N+ CH
C
CH2
CH3
H
H3
OH
( )12
sphingosineH2C
HC
OH
CH
NH CH
C
CH2
CH3
H
OH
( )12
C
R
O
ceramide
The amino group of sphingosine can form an amide bond with a fatty acid carboxyl, to yield a ceramide.
Sphingomyelin, with a phosphocholine head group, is similar in size and shape to the glycerophospholipid phosphatidyl choline.
Sphingomyelin has a phosphocholine or phosphethanolamine head group. Sphingomyelins are common constituent of plasma membranes.
H2CHC
O
CH
NH CH
C
CH2
CH3
H
OH
( )12
C
R
O
PO O
OH2C
H2CN+
CH3
H3C
CH3
Sphingomyelin
phosphocholine
sphingosine
fatty acid
Cholesterol is largely hydrophobic.
But it has one polar group, a hydroxyl, making it amphipathic.
C holesterolH O
Cholesterol, an important constituent of cell membranes, has a rigid ring system and a short branched hydrocarbon tail.
cholesterol PDB 1N83
Structural features of cholesterol (Chol) and cholesteryl esters (Chol-esters)
CholesterolFour fused hydrocarbon rings (A, B, C, and D, called the "steroid nucleus"C8 branched hydrocarbon chain attached to C17Hydroxyl group at C-3 Double bond between C-5 and C-6 Sterols: Steroids with 8 to 10 C in sides chain and hydroxyl group at C-3 Cholesterol does not occur in plantsCholesteryl estersMost plasma cholesterol is in an esterified form.More hydrophobic than CholNot in membranes
Cholesterolin membrane
Cholesterol inserts into bilayer membranes with its hydroxyl group oriented toward the aqueous phase & its hydrophobic ring system adjacent to fatty acid chains of phospholipids.
The OH group of cholesterol forms hydrogen bonds with polar phospholipid head groups.
C holesterolH O
Two strategies by which phase changes of membrane lipids are avoided: Cholesterol is abundant in membranes, such as
plasma membranes, that include many lipids with long-chain saturated fatty acids. In the absence of cholesterol, such membranes would crystallize at physiological temperatures.
The inner mitochondrial membrane lacks cholesterol, but includes many phospholipids whose fatty acids have one or more double bonds, which lower the melting point to below physiological temperature.
Biochemistry IIMembrane lipids / Cholesterol Introduction to
lipids
Testosterone, the male sex hormone, is produced in the testes. Estradiol, one of the female sex hormones, is produced in the ovaries and placenta. Cortisol and aldosterone are hormones synthesized in the cortex of the adrenal gland; they regulate glucose metabolism and salt excretion.Prednisolone and prednisone are synthetic steroids used as antiinflammatory agents.
• Anabolic steroids (Athletes)TestosteroneIncrease of body mass, strengthSide effects (men) liver cancer, impotenceHypercholesterolemiaBreast growthSide effects (women) increased amount of
body hairVoice deepeningMenstrual irregularities
Biochemistry IIMembrane lipids / Cholesterol
Introduction to lipids
AtherosclerosisForm of ateriosclerosis resulting from the
deposition of lipids, primarily TAGs, and Chol, from the blood stream
Chol. is the larger threatWe have to reduce lipid intakeUnstaurated fish and vegetable oil Loweing of
Chol levelNormal Chol level = 200-220 mg/dlElevated Chol level should be cotrolled by dietIn extreme cases cholesterol lowering drungs
(pravastatin, lovastatin)
GM2
Sphingomyelin
Glycosphingolipids differ from sphingomyelin in that they do not contain phosphate.The polar head function is provided by a monosaccharide or oligosaccharide attached directly to the ceramide by an o-glycosidic bond.
Structure Of glycosphingolipids
The simplest neutral (uncharged) glycosphingolipids are the cerebrosides (ceramide + galactose or ceramide + glucose).They serves primarily as an intermediate in the synthesis and degradation of the more complex glycosphingolipids).The cerebroside are found predominantly in the brain and peripheral nervous tissue.Ceramide oligosaccharides (or globosides) are produced by attaching additional monosaccharides (including GalNAc).
Neutral glycosphingolipidsO
O HO
O H
OO
O H
OO H
H O
H O(C H2)1 2 C
HN (C H2)1 6 C H3
O
O H
Lactosylceramide (Gal- b 1,4-Glc- b 1,1'-Cer)
globo-
GalNAc- b 1,3-Gal- a1,4-
OH
O
O H
N H A c
H O
H OO
O H
OO
O H
Galactosylceramide
H OO H
O
O H
O
( C H 2 ) 1 2 C H 3
H N ( C H 2 ) 1 6 C H 3
O H
O H
Glucosylceramide
H OO H
O
O H
O
( C H 2 ) 1 2 C H 3
H N ( C H 2 ) 1 6 C H 3
O H
H O
O O
Eicosanoids participate in many processes in the body:Inflammatory response that occurs after infection or injury with symptoms such as pain, swelling, and fever. An exaggerated or inappropriate expression of the normal inflammatory response may occur in individuals who have allergic or hypersensitivity reactionsContraction of smooth muscles (particularly in the intestine and uterus)Increase in the excretion of water and sodium by the kidneyRegulation of blood pressureRegulation of bronchoconstriction and bronchodilation (modulators)
Functions of the Eicosanoids
Biosynthesis of the Eicosanoids
Cyclooxygenase Pathway: Synthesis of the Prostaglandins and Thromboxanes
1. Synthesis of PGH2
Oxidative cyclization of free arachidonic acid by prostaglandin endo-peroxide synthase PGH2 !!!!
PGH2!!!! variety of prostaglandins and thromboxanesProstaglandin endoperoxide synthase-2 activities (COX and peroxidase)
2 isoenzymes (COX1 and COX2) [2 O2 molecules]COX1: (in most tissues): maintenance of healthy gastric tissue, renal homeostasis, and platelet aggregation.COX2: (inducible in a limited number of tissues) in response to products of activated immune and inflammatory cells.
Cyclooxygenase Pathway: Synthesis of the Prostaglandins and Thromboxanes
2. Inhibition of prostaglandin synthesis Cortisol (a steroidal anti-inflammatory agentinhibition of PLA2, COX2 but not COX1.NSAIDS (nonsteroidal anti-inflammatory agents (e.g. Aspirin) inhibition of COX1 and COX2 damage to the stomach and the kidneys, and impaired clotting of blood, is the basis of aspirin's toxicity.Specific inhibitors for COX2 (for example, celecoxib1) are designed to reduce pathologic inflammatory processes while maintaining the physiologic functions of COX2.