Chapter 10: Lipids

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Transcript Chapter 10: Lipids

Lipids
Lipids

One of 4 major classes of compounds found in living
tissue
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Oils, fats, or fat-like material
Some vitamins, hormones
Not polymeric
Aggregate
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Nucleic acids, proteins, carbohydrates, lipids
Structural matrix of biological membranes
Structural variety
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Largely hydrophobic
Insoluble in water
Soluble in organic solvents (chloroform, ether)
Outline
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Storage
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Structural
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Fatty acids
Triacylglycerols
Phospholipids
Glycolipids
Sterols
Other lipids
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Fat-soluble vitamins
Eicosanoids
Lipid Characteristics
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Hydrophobic
Ratio of H to O is much
greater than 2:1
For example…
C18H34O3
Lipid Structure
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Glycerol
2 monomers
More bonds means
more Energy!
Fatty acid
Hydrocarbon chains
C55H102O6
Lipid Functions
1.
2.
3.
4.
5.
6.
Surround and contain aqueous cell contents
(plasma membranes)
Chemical signals from cell to cell
(hormones and steroids)
Energy storage (fats)
Cushion and protect internal organs
Insulate body (subcutaneous fat)
Lubricate skin and hair, prevent cracking
(oils)
Lipid Functions: Surround and contain aqueous cell
contents (plasma membranes)
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Lipid Functions:
Hormones and Steroids
Chemical messengers
4 fused ring structure
Hydrophobic
Estrogen & testosterone are sex hormones, they act as
chemical signals
Lipid Functions: Hormones
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and Steroids
Cholesterol is a steroid. It is essential to healthy cell
membranes
Also, other steroids are made from cholesterol
But
cholesterol
cardiovascular disease !!
Fatty Acids
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Simplest type; components of more complex lipids
Carboxylic acids with long aliphatic hydrocarbon chains
Generally 10-20 carbons
 Most common are 16, 18
 Mostly even number due to synthesis
Saturated or unsaturated
Saturated Fatty Acids
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Only C─C
Highly flexible
Most stable conformation = fully extended
mp increase with chain length
ex: stearic acid (octadecanoic acid)
O
OH
1
18
Know the
names of all
FA’s given in
this PPT
Unsaturated Fatty Acids
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Contains C═C
Can be polyunsaturated
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First double bond typically at C9
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D9
Double bonds every three carbons
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essential FAs
D9,12
─CH═CH─CH2─CH═CH─CH2─
ex: oleic acid (18:1) and linoleic acid (18:2)
18
OH
OH
O
1
O
18
12
9
9
1
Omega-3 Fatty Acids
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Corn, fish oil
Reduce possibility of heart disease
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Don’t stick to walls of blood vessels
Promote blood flow
ex: linolenic acid
18
O
OH
1
Unsaturated Fatty Acids
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Double bonds
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Typically cis or trans?
Causes bend in hydrocarbon chain
Do not pack as well as saturated FAs
mp decrease as unsaturation increases
Triacylglycerols
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aka triacylglycerides
Fatty acid triesters of glycerol
Simple
Mixed
Triacylglycerols
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Most abundant class of lipids in animals
mp determined by degree of unsaturation
More unsaturation in plants than in animals
Function = energy reserves, insulation
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Better source of E than carbohydrates
Stored in adipocytes throughout the body
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Hydrolyzed by lipases as needed
Soaps
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Soaps form water-insoluble salts when used
in water containing Ca(II), Mg(II), and Fe(III)
ions (hard water)
-
2 CH3 ( CH2 ) 1 4 COO Na
A s odium soap
(soluble in water as micelles )
+
+
Ca
2+
-
[ CH3 ( CH2 ) 1 4 COO ] 2 Ca
Calcium salt of a fatty acid
(insoluble in water)
2+
+
2 Na
+
Fatty acids in food
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Triacylglycerols and free FAs
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“Fat” = mostly saturated
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Animal sources (meat, butter)
“Oil” = mostly unsaturated
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Saturated = solid at rt
Unsaturated = liquid at rt
Plant sources (olive, peanut)
Partial hydrogenation
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Raise mp (semi-solid)
Soft margarine, etc.
More sat fat but less cholesterol
than butter
Side effect = production of trans FAs
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Behave like saturated fat
Increases LDL levels
Decrease HDL levels
Structural Lipids
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Amphipathic
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Hydrophobic chain(s)
Hydrophilic (-OH or larger)
Pack into bilayers
Biological membranes
Phospholipids
O
O
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O
O
Contain phosphodiester bond
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P
Negative charge at physiological pH
Example: Glycerophospholipids
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aka phosphoglycerides
Major component of membranes
Esterified glycerol-3-phosphate
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Phosphoryl group linked to polar group (various structure)
L is naturally occurring
D
X
Saturated C16 or C18 FA
Phosphodiester
linkage
Unsaturated C16 – C20 FA
Derived from polar alcohol
• smallest = H (from H-OH)
• least common in membranes
• phosphatidic acid
Structure of Glycerophospholipids
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Determined by analysis of products from enzymecatalyzed hydrolysis
Phospholipases
Cleave specific bonds
Enzymes are small
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Only section being
cleaved fits in active site
Remainder of lipid in
non-aqueous environment
or stabilized by nonpolar
AA side chains
Plasmalogens
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One type of glycerophospholipid
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C1 linkage is a,b-unsaturated ether (not ester)
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Heart tissue of vertebrates
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Membranes of some invertebrates and bacteria
Glycolipids
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Monosaccharide or
oligosaccharide at polar
end
Example: Galactolipids
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Galactose residues
Glycosidic linkages to C3
of 1,2-diacylglycerol
Plant cells
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Internal membranes of
chloroplasts
Sphingolipids
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Also major component of membranes
Phospholipid or glycolipid (depends on polar group)
Derivatives of sphingosine (instead of glycerol)
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C18 amino alcohol
Ceramide
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Acylated amine
Parent compound of most abundant sphingolipids
• Polar head group  derivatives
• Phosphodiester or glycosididic
or linkage
Phospholipid
Phosphate derivative
structurally similar to
glycerophospholipids
Glycosphingolipids
monosaccharide
neutral; 2 or more
sugars (Glc, Gal, or
GalNac)
oligosaccharide;
N-acetyl
neuraminic acid;
negative at pH 7
Glycerophospholipids/Sphingolipids
 Structural similarities
Back
Waxes
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An ester of a long-chain fatty acid and alcohol
 from the Old English word weax = honeycomb
O
O
CH3 ( CH2 ) 1 4 CO( CH2 ) 2 9 CH3
A major component of beeswax
(honeycombs)
CH3 ( CH2 ) 3 0 CO( CH2 ) 3 3 CH3
A major component of
carnauba wax
(the Brazilian wax palm)
O
CH3 ( CH2 ) 1 4 CO( CH2 ) 1 5 CH3
A major component of
spermacetti wax
(head of the s perm whale)
Sterols
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Sterol
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Four fused rings
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One or more hydroxyl groups
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Gives amphipathic character
Hydrocarbon side chain
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Greater rigidity than other
membrane lipids
Length of C16 FA
Cholesterol
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Most abundant sterol in animals
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Produced by liver; supplied by diet
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High levels lead to gallstones and
deposits on arteries (plaque)
Sterols
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Metabolic precursors of steroid
hormones
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Regulate physiological functions
Androgens (testosterone)
Estrogens (b-estradiol)
Glucocorticoids (cortisol)
Insoluble in water
Bind to proteins for transport to
target tissue
Vitamin D
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Sterol derivatives
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Function
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Regulate Ca and P absorption
during bone growth
Sources
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Open B rings
Diet: D2 (milk additive, plant
sources) and D3 (animal
sources)
Precursor: intermediate in
cholesterol synthesis
Formed in skin nonenzymatically from 7dehydrocholesterol
Deficiency
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Soft bones, impaired growth and
skeletal deformities in children
Inactive form
Other Lipids
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Classified on basis of physical properties
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Fat-soluble vitamins
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Solubility
Hydrophobicity
Amphiphilicity
Vitamins A, E, K (and D)
Isoprenoids
Eicosanoids
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Prostaglandins
Thromboxanes
Leukotrienes
Vitamin A
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Collective term for retinol, retinal, retinoic acid
Formed from oxidative cleavage of b-carotene
in liver
Function
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Aldehyde: visual cycle/process, component of
rhodopsin (visual pigment)
Alcohol, carb acid: growth, reproduction
Deficiency
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Night blindness
Xerophthalmia
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Dryness in eyes
No tear production
Damage to cornea
Leads to blindness
Vitamin K
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Phylloquinone or menaquinone
Function
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K1 = plants; K2 = animals
Bacteria in intestine
CH3
O
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Unlikely due to synthesis and wide
distribution in food
Injection for infants
Hemolytic anemia = destruction of red
blood cells
CH3
O
CH3
Toxicity
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Jaundice from large doses of vit. K, toxic
effects on membrane of red blood cells,
cells die, lead to increased levels of
yellow bilirubin (formed from heme)
CH3
Vitamin K1 (phylloquinone)
Deficiency
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CH3
Synthesis of blood clotting proteins
Sources
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O
CH3
O
CH3
CH3
Vitamin K2 (menaquinone)
Vitamin E
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a-tocopherol
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Function
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Antioxidant: prevents cell damage from oxidation of polyunsaturated FAs
in membranes by O2 and free radicals
Deficiency
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Associated with defective lipid transport/absorption
Olestra
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Artificial, noncaloric fat substitute (indigestible)
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FDA warning
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“This Product Contains Olestra. Olestra may cause abdominal cramping
and loose stools. Olestra inhibits the absorption of some vitamins and
other nutrients. Vitamins A, D, E, and K have been added.”
O
R
O
C
O
C
CH 2
O
O
H
O
H
O
CH 2
H
R
R
O
H
O
O
H
O
C
H
C
CH 2
O
O
O
C
C
H
O
H
O
R
R
O
R
C
O
R
R
Olestra
R = (CH2)8-22CH3
O
Eicosanoids
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Hormones involved in production of pain, fever, inflammatory
reactions
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Prostaglandins
Thromboxanes
Leukotrienes
Metabolites of arachidonic acid (a polyunsatruated FA)
Synthesis inhibited by NSAIDs
 e.g. acetylsalicylic acid (aspirin)
 Acylate Ser residue, preventing access to active site
Steroids
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The features common to the ring system of
most naturally occurring steroids are
illustrated here
CH3
H
H
CH3
H
H
Androgens
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Androgens: male sex hormones
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synthesized in the testes
responsible for the development of male
secondary sex characteristics
H3 C
H3 C
OH
H
H
H
O
H3 C
H3 C
H
H
H
HO
Testosterone
Androsterone
H
O
Estrogens
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Estrogens: female sex hormones
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synthesized in the ovaries
responsible for the development of female
secondary sex characteristics and control
of the menstrual cycle
CH3
H3 C
H3 C
C= O
H
H 3 C OH
H
H
H
O
H
H
HO
Proges terone
Estradiol
H