2. IMPORTANCE OF LIPIDS
• They are the structural component of cell membranes.
• They help in providing energy and produce hormones in our body.
• Fat is stored in adipose tissue, where it also serves as a thermal insulator in the
subcutaneous tissues and around certain organs.
3. IMPORTANCE OF LIPIDS
• Nonpolar lipids act as electrical insulators, allowing rapid propagation of depolarization
waves along myelinated nerves.
• Combinations of lipid and protein (lipoproteins) serve as the means of transporting
lipids in the blood.
• Lipids play crucial roles as enzyme cofactors, electron carriers, light absorbing pigments,
hydrophobic anchors for proteins, “chaperones” to help membrane proteins fold,
emulsifying agents in the digestive tract, hormones, and intracellular messengers.
4. LIPIDS
• Heterogeneous group of compounds or esters of fatty acids, including fats, oils,
steroids, waxes, and related compounds.
• Also known as triglycerides
• Insoluble in water
• Soluble in nonpolar solvents such as ether and chloroform
7. FATTY ACIDS
• Building blocks of the fats and oils.
• Aliphatic chains of carboxylic acids consisting of a straight alkyl chain, terminating with a carboxyl group
• Alkyl chain range from 4 to 36 carbons (C4 to C36).
• Carbon atoms are numbered from the carboxyl carbon (carbon No. 1).
• The carbon atoms adjacent to the carboxyl carbon (Nos. 2, 3, and 4) are also known as the α, β, and γ carbons,
respectively, and the terminal methyl carbon is known as the ω- or n-carbon.
8. FATTY ACIDS
• ω9 indicates a double bond on the ninth carbon counting from the ω-carbon.
• In animals, additional double bonds are introduced only between the existing double
bond (e.g, ω9, ω6, or ω3) and the carboxyl carbon, leading to three series of fatty
acids known as the ω9, ω6, and ω3 families, respectively.
10. FATTY ACIDS
• Fatty acids occur in the body mainly as esters in natural fats and oils, but are found
in the un-esterified form as free fatty acids, a transport form in the plasma.
• The chain may be:
• Saturated and unbranched (containing no double bonds)
• Unsaturated and branched (containing one or more double bonds)
12. SATURATED FATTY ACIDS
• Unbranched
• No double bonds
• Short- and medium-chain saturated fatty acids (4 to 12 carbons in length)
• Other animal and vegetable fats contain predominantly longer-chain (more than 14
carbons in length)
13. UNSATURATED FATTY ACIDS
• Branched
• Have double bonds
• They can be:
• Monounsaturated (monoethenoid, monoenoic) acids, containing one double bond.
• Polyunsaturated (polyethenoid, polyenoic) acids, containing two or more double bonds.
17. CLASSIFICATION OF LIPIDS
• On the basis of structure, lipids are classified as:
• Simple Lipids
• Complex Lipids
18. SIMPLE LIPIDS
• Esters of fatty acids with various alcohols.
• Fats: Esters of fatty acids with glycerol. Saturated and solids at room temperature.
• Oils: Oils are fats in the liquid state. Unsaturated fatty acids.
• Waxes: Esters of fatty acids with higher molecular weight monohydric alcohols.
19. COMPLEX LIPIDS
• Esters of fatty acids containing groups in addition to an alcohol and a fatty acid.
• Phospholipids: Lipids containing, in addition to fatty acids and an alcohol, a phosphoric acid
residue.
• They frequently have nitrogen containing bases and other substituents, e.g, in
glycerophospholipids the alcohol is glycerol and in sphingophospholipids the alcohol is
sphingosine.
• Glycolipids (glycosphingolipids): Lipids containing a fatty acid, sphingosine, and
carbohydrate.
20. COMPLEX LIPIDS
• Other complex lipids: Lipids such as sulfo lipids and amino lipids. Lipoproteins may
also be placed in this category.
• Precursor and derived lipids: These include fatty acids, glycerol, other alcohols,
fatty aldehydes, hydrocarbons, lipid-soluble vitamins, and hormones.
• Because they are uncharged, acylglycerols (glycerides), cholesterol, and cholesteryl
esters are termed neutral lipids.
22. STORAGE LIPIDS
• Triacylglycerols provide stored energy and insulation.
• In eukaryotes, triacylglycerols form a separate phase of microscopic, oily droplets in
the aqueous cytosol, serving as depots of metabolic fuel.
• In vertebrates, specialized cells called adipocytes, or fat cells, store large amounts of
triacylglycerols as fat droplets that nearly fill the cell.
23. STORAGE LIPIDS
• Adipocytes contain lipases enzymes that catalyze the hydrolysis of stored
triacylglycerols, releasing fatty acids for export to sites where they are required as
fuel.
• In some animals, triacylglycerols stored under the skin serve not only as energy
stores but as insulation against low temperatures.
• Carbohydrates such as glucose and glycogen do offer certain advantages as quick
sources of metabolic energy, one of which is their ready solubility in water.
24. STORAGE LIPIDS
• Two significant advantages to using triacylglycerols as stored fuels, rather than
polysaccharides such as glycogen and starch are:
• They yield more energy
• They are hydrophobic and therefore unhydrated, the organism that carries fat as fuel
does not have to carry the extra weight of water of hydration that is associated with
stored polysaccharides.
• They can be stored for much longer period of time as compared to carbohydrates.
25. STORAGE LIPIDS
• Biological waxes are esters of long-chain (C14 to C36) saturated and unsaturated
fatty acids with long-chain (C16 to C30) alcohols.
• Waxes also serve a diversity of other functions related to their water-repellent
properties and their firm consistency.
• Certain skin glands of vertebrates secrete waxes to protect hair and skin and keep it
pliable, lubricated, and waterproof.
27. MEMBRANE LIPIDS
• Biological membrane is a double layer of lipids, which acts as a barrier to the
passage of polar molecules and ions.
• Membrane lipids are amphipathic:
• one end of the molecule is hydrophobic
• other end is hydrophilic
• Their hydrophobic interactions with each other and their hydrophilic interactions
with water direct their packing into sheets called membrane bilayers.
28. MEMBRANE LIPIDS
• Membrane lipids can be:
• Glycerophospholipids
• Ether Lipids
• Sphingolipids
• Sterols and Cholesterol
30. GLYCEROPHOSPHOLIPIDS
• Glycerophospholipids (phosphoglycerides) are derivatives of phosphatidic acid (fatty
acid).
• Membrane lipids which contain two fatty acids attached in ester linkage to the first
and second carbons of glycerol.
• A highly polar or charged group (head group) is attached through a phosphodiester
linkage to the third carbon.
32. ETHER LIPIDS
• Ether lipids, in which one of the two acyl chains is attached to glycerol in ether,
rather than ester, linkage.
• The ether-linked chain may be saturated, as in the alkyl ether lipids, or may contain
a double bond between C-1 and C-2, as in plasmalogens.
• Vertebrate heart tissue is uniquely enriched in ether lipids; about half of the heart
phospholipids are plasmalogens.
34. ETHER LIPIDS
• Another example of ether lipids is platelet-activating factor, a potent molecular
signal.
• It is released from leukocytes called basophils and stimulates platelet aggregation
and the release of serotonin (a vasoconstrictor) from platelets.
• It also exerts a variety of effects on liver, smooth muscle, heart, uterine, and lung
tissues and plays an important role in inflammation and the allergic response.
36. SPHINGOLIPIDS
• Sphingolipids a polar head group and two nonpolar tails, but unlike
glycerophospholipids they contain no glycerol.
• Sphingolipids are composed of:
• one molecule of the long-chain amino alcohol sphingosine (also called 4-sphingenine) or
one of its derivatives,
• one molecule of a long-chain fatty acid
• a polar head group that is joined by a glycosidic linkage in some cases and by a
phosphodiester in others.
38. SPHINGOLIPIDS
• Carbons C-1, C-2, and C-3 of the sphingosine molecule are structurally analogous to
the three carbons of glycerol in glycerophospholipids.
• When a fatty acid is attached in amide linkage to the ONH2 on C-2, the resulting
compound is a ceramide.
40. SPHINGOLIPIDS
• Sphingolipids at cell surfaces are sites of biological recognition.
• Many of these are especially prominent in the plasma membranes of neurons
• The carbohydrate moieties of certain sphingolipids define the human blood groups
and therefore determine the type of blood that individuals can safely receive in blood
transfusions.
42. STEROLS AND CHOLESTEROL
• Sterols are structural lipids present in the membranes of most eukaryotic cells.
• Contain steroid nucleus, consisting of four fused rings, three with six carbons and
one with five.
• Cholesterol, the major sterol in animal tissues, is amphipathic containing
• A polar head group (the hydroxyl group at C-3)
• A nonpolar hydrocarbon body (the steroid nucleus and the hydrocarbon side chain at C-
17), about as long as a 16-carbon fatty acid in its extended form.
43. STEROLS AND CHOLESTEROL
• In addition to their roles as membrane constituents, the sterols serve as precursors
for a variety of products with specific biological activities.
• Steroid hormones, for example, are potent biological signals that regulate gene
expression.
46. LIPIDS AS SIGNALS
• Some lipids serve as potent signals—as hormones, carried in the blood from one tissue to
another, or as intracellular messengers generated in response to an extracellular signal
(hormone or growth factor).
• Phosphatidylinositols and sphingosine derivatives act as intracellular signals.
• Eicosanoids are paracrine hormones, substances that act only on cells near the point of
hormone synthesis instead of being transported in the blood to act on cells in other
tissues or organs.
47. LIPIDS AS SIGNALS
• Steroid hormones carry messages between tissues.
• Steroids are oxidized derivatives of sterols; they have the sterol nucleus but lack the
alkyl chain attached to ring D of cholesterol, and they are more polar than cholesterol.
• Steroid hormones move through the bloodstream (on protein carriers) from their site of
production to target tissues, where they enter cells, bind to highly specific receptor
proteins in the nucleus, and trigger changes in gene expression and metabolism.
48. LIPIDS AS SIGNALS
• The major groups of steroid hormones are the male and female sex hormones and
the hormones produced by the adrenal cortex, cortisol and aldosterone.
49. LIPIDS AS COFACTORS
• Some lipids function as enzyme cofactors in:
• electron-transfer reactions in chloroplasts and mitochondria
• transfer of sugar moieties in a variety of glycosylation (addition of sugar) reactions
