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Part 2:
Fats
Prepared by:
Dr A. Riasi ( Isfahan University of Technology)
Reference:
Lehninger Biochemistry
Advance Biochemistry
Isfahan University of Technology
Biological Lipids
Lipids are divides to three original groups:
Fats and oils
Phospholipids and sterols
Other lipids
Storage lipids
Fatty acids are carboxylic acids:
CH3(CH2)n-COOH
Storage lipids
A few contain three-carbon rings, hydroxyl
groups, or methyl group branches.
A simplified nomenclature for these compounds
specifies the chain length and number of double
bonds.
Storage lipids
The positions of any double bonds are specified
by superscript numbers following (Δ).
A 20-carbon fatty acid with one double bond
between C-9 and C-10 and another between C-12
and C-13 is designated as C20:2(Δ9,12).
Storage lipids
The poly unsaturated fatty acid of Arachidonic [20:4
(Δ5,8,11,14)] is an exception to this generalization.
CH3(CH2)4CH=CHCH2CH=CHCH2CH=CHCH2CH=CH(CH2)3COOH14 11 8 5
Storage lipids
CH3-(CH2)7-CH=CH-(CH2)4-CH2-CH2-CH2-COOHω
n
Δαβγ
Storage lipids
In nearly all naturally occurring unsaturated
fatty acids, the double bonds are in the cis
configuration.
Storage lipids
Storage lipids
11
What are the differences between α Linolenic acid and γ Linolenic acids?
Storage lipids
Comparison of the satutare Stearic acid (left), trans
isomer (middle) Elaidic acid and the cis-isomer (right)
Oleic acid.
Storage lipids
Most naturally occurring triacylglycerols are
mixed.
They contain two or more different fatty acids.
Storage lipids
Storage lipids
Storage lipids
Vegetable oils are converted industrially into
solid fats by catalytic hydrogenation.
Storage lipids
Storage lipids
Biological waxes are esters of:
Long-chain (C14 to C36) saturated
Unsaturated fatty acids with long-chain (C16 to
C30) alcohols.
Storage lipids
Storage lipids
There are different generals types of
membrane lipids:
Glycerophospholipids
Galactolipids and Solpholipds
Archaebacterial tetraether lipids
Sphingolipids
Sterols
Phospholipids and sterols
Phospholipids and sterols
Glycerophospholipids and some sphingolipids
are named phospholipids.
Phospholipids and sterols
Other sphingolipids are
the glycolipids.
Phospholipids and sterols
Phospholipids and sterols
The polar alcohol may have
different charge: Negatively charged:
phosphatidylinositol 4,5-
bisphosphate
Neutral: phosphatidylserine
Positively charged:
phosphatidylcholine or
phosphatidylethanolamine
Phospholipids and sterols
The fatty acids in glycerophospholipids can be
any of a wide variety
A given phospholipid may consist of a number
of molecular species, each with its unique
complement of fatty acids.
Phospholipids and sterols
Some animal tissues are rich in ether lipids.
In ether lipids one of the two acyl chains is
attached to glycerol in ether linkage.
Phospholipids and sterols
Two kind of ether lipids:
Ether-linked chain is saturated
Ether-linked chain is unsaturated
Phospholipids and sterols
The functional significance of ether lipids in
these membranes is unknown.
The ether lipid, platelet-activating factor, is a
potent molecular signal.
It is released from leukocytes called basophils.
Phospholipids and sterols
The galactolipids & Solpholipids are
predominate in plant cells.
Phospholipids and sterols
The archaebacteria, most of which live in
ecological niches with extreme condition:
Low pH
High ionic strength
High temprature
Phospholipids and sterols
Phospholipids and sterols
Sphingolipids, have a polar head group and
two nonpolar tails.
Unlike glycerophospholipids and galactolipids
they contain no glycerol.
Phospholipids and sterols
Sphingolipids are composed of:
one molecule of the long-chain amino alcohol
one molecule of a long-chain fatty acid
a polar head group
Phospholipids and sterols
Carbons C-1, C-2, and C-3 of the sphingosine molecule are structurally analogous to the three carbons of glycerol in glycerophospholipids.
Phospholipids and sterols
There are three subclasses of sphingolipids, all
derivatives of ceramide but differing in their
head groups:
Sphingomyelins,
Neutral (uncharged) glycolipids,
Gangliosides.
Phospholipids and sterols
Phospholipids and sterols
Sterols are structural lipids present in the
membranes of most eukaryotic cells.
Cholesterol is the major sterol in animal
tissues, is amphipathic.
Similar sterols are found in other eukaryotes:
stigmasterol in plants and ergosterol in fungi.
Phospholipids and sterols
The sterols serve as precursors for a variety of
products with specific biological activities.
Steroid hormones
Bile acids to make them more readily accessible to
digestive lipases.
Phospholipids and sterols
Steroids are oxidized derivatives of sterols
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.
Phospholipids and sterols
The major groups of steroid hormones are the
male and female sex hormones and the
hormones produced by the adrenal cortex.
Phospholipids and sterols
Prednisone and prednisolone are steroid drugs
with potent antiinflammatory activities.
They have a variety of medical applications,
including the treatment of asthma and
rheumatoid arthritis.
Phospholipids and sterols
Phospholipids and sterols
Eventually the fat-soluble group was resolved
into the four vitamin groups A, D, E, and K,
all of which are isoprenoid compounds.
Two of these (D and A) serve as hormone
precursors.
Phospholipids and sterols
Vitamin D3, also called cholecalciferol, is
normally formed in the skin from 7-
dehydrocholesterol in a photochemical
reaction driven by the UV component of
sunlight.
Phospholipids and sterols
Vitamin D3 is not itself biologically active, but
it is converted by enzymes in the liver and
kidney to 1,25-dihydroxycholecalciferol.
Vitamin D2 (ergocalciferol) is a commercial
product formed by UV irradiation of the
ergosterol of yeast.
Phospholipids and sterols
Vitamin D2 is structurally similar to D3, with
slight modification to the side chain attached
to the sterol D ring.
Phospholipids and sterols
Like steroid hormones, the product of vitamin
D metabolism, 1,25-dihydroxycholecalciferol,
regulates gene expression—for example,
turning on the synthesis of an intestinal Ca2-
binding protein.
Phospholipids and sterols
Vitamin A (retinol) in its various forms
functions as a hormone.
The vitamin A derivative, retinoic acid,
regulates gene expression in the development
of epithelial tissue, including skin.
Phospholipids and sterols
The vitamin A derivative, retinal, is the
pigment that initiates the response of cells of
the retina to light, producing a neuronal signal
to the brain.
Phospholipids and sterols
In vertebrates, -carotene, the pigment that
gives carrots, sweet potatoes, and other yellow
vegetables their characteristic color, can be
enzymatically converted to vitamin A.
Phospholipids and sterols