1 18.1lipids 18.2fatty acids chapter 18 lipids. 2 lipids lipids are: biomolecules that contain fatty...
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18.1 Lipids
18.2 Fatty Acids
Chapter 18 Lipids
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Lipids
Lipids are: 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.
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Diversity in structure leads to a diversity in biological function Non-polar lipids (fats) are the principal molecules for
energy storage Polar lipids (nitrogen and phosphorus containing) are
components of biological membranes The steroid class of lipids (cholesterol) is found in
biological membranes and used as a precursor for many hormones
Miscellaneous lipids present only in minor quantities in the cell are involved as light-absorbing pigments (β-carotene, retinal), enzyme cofactors (vitamin K), signal molecules (prostaglandins), and electron carries (ubiquinone)
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Classes of Lipids
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Fatty acids are: Long-chain carboxylic acids that have
an even number (usually 12-18) of carbon atoms.
Insoluble in water. Saturated or unsaturated.
Fatty Acids
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Fatty Acid Formulas The formulas for fatty acids are written as
condensed and line-bond formulas. For example caprylic acid with 8 carbon atoms can be written as:
CH3—(CH2)6—COOH
CH3—CH2—CH2—CH2—CH2—CH2—CH2—COOH O
||CH3—CH2—CH2—CH2—CH2—CH2—CH2—C—OH
OH
O
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Ionization General fatty acid formula: R – COOH (R stands for alkyl chain composed of carbon
and hydrogen atoms) The pKa of the fatty acid carboxyl group is about 4.8 Under ordinary conditions the pH of the plasma is 7.4, and
the pH of the intracellular fluid is about 7.0 Almost all (99.9%) of the free fatty acid molecules in body
fluids are ionized (the fatty acid is present as an anion) RCOOH ↔ RCOO- + H+
The ionized group interacts with aqueous media (polar) The hydrocarbon “tail” seeks a non-polar environment
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General nomenclature The carbon atoms of an acid are numbered (or
lettered with Greek lettering system, such as α, β, γ) either from the carboxyl group or from the carbon farthest removed from the carboxyl group (n or omega numbering system)
CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-COOH 10 9 8 7 6 5 4 3 2 1 1 2 3 4 5 6 7 8 9 10 ω δ γ β α
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Saturated Fatty AcidsSaturated fatty acids have single C–C bonds.
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Systematic namesComponents Common name Systematic name
1 formic methanoic
2:0 acetic ethanoic
3:0 propionic propanoic
4:0 butyric butanoic
5:0 valeric pentanoic
6:0 caproic hexanoic
8:0 caprylic octanoic
10:0 capric decanoic
12:0 lauric dodecanoic
14:0 mystiric tetradecanoic
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Systematic names (continue)Components Common name Systematic name
16:0 palmitic hexadecanoic
16:1 (9) palmitoleic cis-9-hexadecenoic
18:0 stearic octadecanoic
18:1 (9) oleic cis-9-octadecenoic
18:1 (11) vaccenic cis-1-octadecenoic
18:2 (9,12) linoleic all cis-9,12-octadecadienoic
18:3 (9,12,15) linolenic all cis-9,12,15-octadecatrienoic
20:0 arachidic eicosanoic
20:4 (5,8,11,14) arachidonic all cis-5,8,11,14-eicosatetraenoic
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Saturated fatty acids have: Molecules that fit closely
together in a regular pattern. Strong attractions between
fatty acid chains. High melting points that
makes them solids at room temperature.
Saturated Fatty Acids
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Unsaturated Fatty Acids Unsaturated fatty acids typically
contain cis double bonds.
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Unsaturated Fatty AcidsUnsaturated fatty acids have cis C=C bonds.
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Unsaturated fatty acids: Have nonlinear
chains that do not allow molecules to pack closely.
Have low melting points.
Are liquids at room temperature.
Unsaturated Fatty Acids
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Olive Oil
Olive oil contains a high percentage of oleic acid.
Oleic acid is a monounsaturated fatty acid with one cis double bond.
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Melting Points of Fats and OilsVegetable oils contain more unsaturated fatty acids,
which makes their melting points lower.
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Canola oil Canola Oil - Truth and Myths about Canola http://www.canola-council.org/about/
thetruth.html
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Omega-6 and Omega-3 Fatty Acids
The first double bond: In vegetable oils is at carbon 6 (omega-6). In fish oils is at carbon 3 (omega-3).
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Essential fatty acids Mammals cannot synthesize the two main types of polyunsaturated
fatty acids: the linoleic (omega-6) and linolenic (omega-3) Essential fatty acid deficiency is characterized by dermatitis and poor
wound healing Most prostaglandins are synthesized from arachidonic acid (a linoleic
acid derivative) Lack of these prostaglandins causes some aspects of the essential fatty
acid deficiency syndrome A small daily intake of linolenic acid is recommended (this may be
especially important when the nervous system is developing) Docosahexaenoic acid (22:6n-3) – omega-3 fatty acid is needed for
maximum development of the visual and central nervous systems during the neonatal period (it is present in large amounts in the retina and parts of the brain; it enhances the visual response and the function of certain domains in neural membranes)
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ProstaglandinsProstaglandins have: 20 carbon atoms in their fatty acid chains. An OH on carbon 11 and 15. A trans double bond at carbon 13.
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Prostaglandins in the BodyProstaglandins are: Produced by injured tissues. Involved in pain, fever, and
inflammation. Not produced when anti-
inflammatory drugs such as aspirin inhibit their synthesis.
Prostaglandins http://www.elmhurst.edu/
~chm/vchembook/555prostagland.html
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Other eicosanoids When a cell responds to a stimulus, bioactive
mediators (prostaglandins, thromboxanes, leukotrienes, and others) often are formed from the lipids contained in its membranes.
Thromboxanes regulate blood coagulation. Leukotrienes play a role in allergic and
inflammation responses. They were isolated from leukocytes (white blood cells).
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