Andy Howard
Introductory Biochemistry
28 February 2008

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Carbohydrates
(concluded)
 Lipids
 Glycosphingolipids
 Glycoconjugates
 Isoprenoids
 Proteoglycans
 Steroids
 Peptidoglycans
 Other lipids
 Glycoproteins
 Membranes
Lipids
 Bilayers
 Lipid characteristics
 Fluid mosaic model
 Fatty acids
Physical properties
 Phospholipids

 Lipid Rafts
Biochemistry: Lipids p. 2 of 26

 Poly or oligosaccharides covalently linked to proteins or peptides
 Generally heteroglycans
Image courtesy
Benzon Symposia
 Categories:
 Proteoglycans
(protein+glycosaminoglycans)
 Peptidoglycans (peptide+polysaccharide)
 Glycoproteins (protein+oligosaccharide)
Biochemistry: Lipids p. 3 of 26

 Unbranched heteroglycans of repeating disaccharides
 One component is
GalN, GlcN, GalNAc, or GlcNAc

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Other component: an alduronic acid
—OH or —NH2 often sulfated
 Found in cartilage, joint fluid
Biochemistry: Lipids p. 4 of 26

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Highly hydrated, voluminous
Mesh structure
(fig.8.29 or this fig. from Mathews & Van
Holde)
Aggrecan is major proteoglycan
Typical of proteoglycans in that it’s extracellular
Biochemistry: Lipids p. 5 of 26

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Polysaccharides linked to small proteins
Featured in bacterial cell walls: alternating GlcNAc + MurNAc linked with

-
(1

4) linkages
Lysozyme hydrolyzes these polysaccharides
Peptide is species-specific: often contains Damino acids
Biochemistry: Lipids p. 6 of 26

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Gram-negative: thin peptidoglycan layer separates two phospholipid bilayer membranes
Gram-positive: only one bilayer, with thicker peptidoglycan cell wall outside it
Gram stain binds to thick wall, not thin layer
(note misprint on p.244)
 Fig. 8.31 shows multidimensionality of this wall
Biochemistry: Lipids p. 7 of 26

 1-30 carbohydrate moieties per protein
 Proteins can be enzymes, hormones, structural proteins, transport proteins
 Microheterogeneity: same protein, different sugar combinations
 Eight sugars common in eukaryotes
 PTM glycosylation much more common in eukaryotes than prokaryotes
Biochemistry: Lipids p. 8 of 26

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Variety of sugar monomers
 or
 glycosidic linkages
Linkages always at C-1 on one sugar but can be C-2,3,4,6 on the other one
Up to 4 branches
But: not all the specific glycosyltransferases you would need to get all this diversity exist in any one organism
Biochemistry: Lipids p. 9 of 26

O-linked and Nlinked oligosaccharides
 Characteristic sugar moieties and attachment chemistries
Biochemistry: Lipids p. 10 of 26

 GalNAc to Ser or Thr; often with gal or sialic acid on GalNAc
 5-hydroxylysines on collagen are joined to D-Gal
 Some proteoglycans joined via
Gal-Gal-Xyl-Ser
 Single GlcNac on ser or thr
Biochemistry: Lipids p. 11 of 26

 Generally linked to Asn
 Types:
 High-mannose
 Complex
(Sialic acid, …)
 Hybrid
(Gal, GalNAc, Man)
Biochemistry: Lipids
Diagram courtesy
Oregon State U.
p. 12 of 26

 Hydrophobic biomolecules; most have at least one hydrophilic moiety as well
 Attend to fig. 9.1: periodic table of lipids
 Functions
 Membrane components
 Energy-storage molecules
 Structural roles
 Hormonal and signaling roles
Biochemistry: Lipids p. 13 of 26

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Unbranched hydrocarbons with carboxylate moieties at one end
Usually (but not always) even # of C’s
Zero or more unsaturations: generally cis
Unsaturations rarely conjugated (why?)
Resting concentrations low because they could disrupt membranes saturated unsaturated
Biochemistry: Lipids p. 14 of 26

 Not completely absent in biology
 But enzymatic mechanisms for breakdown of cis fatty acids are much more fully developed
 Trans fatty acids in foods derived from
(cis-trans) isomerization that occurs during hydrogenation, which is performed to solidify plant-based triglycerides
Biochemistry: Lipids p. 15 of 26

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Longer chain
 higher MP because longer ones align readily
More unsaturations
 lower MP
 Saturated fatty acids are entirely flexible; tend to be extended around other lipids
 Unsaturations introduce inflexibilities and kinks
Biochemistry: Lipids p. 16 of 26

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Bacterial lipids
• Mostly C
12
-C
18
• 
1 unsaturation
Plant lipids
 High concentration of unsaturated f.a.s
 Includes longer chains
 Animal lipds
 Somewhat higher concentrations of saturated f.a.’s
 Unsaturations four carbons from methyl group (omega f.a.) common in fish oils
Biochemistry: Lipids p. 17 of 26

Beef Soybean
Other
Linoleic
Palmitic
Stearic
Other
Palmitic
Oleic Oleic
Linoleic
Stearic
 Courtesy Charles Ophardt,
Elmhurst College
Biochemistry: Lipids p. 18 of 26

 IUPAC names: hexadecanoic acid, etc.
 Trivial names from sources (Table 9.1)
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Laurate (dodecanoate)
Myristate (tetradecanoate)
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Palmitate (hexadecanoate)
Palmitoleate ( cis -

9 -hexadecenoate)
Oleate ( cis -

9 -octadecenoate)
Linoleate ( cis,cis -

9,12 -octadecadienoate)
Arachidonate
(all cis -

5,8,11,14 -eicosatetraeneoate)
Biochemistry: Lipids p. 19 of 26

70
65
60
55
50
45
40
8
90
85
80
75
12
Melting points for saturated FAs
Contrast with melting points of
Unsaturated C18 FAs:
16ºC, -5ºC -11ºC;
C20, 4 double bonds:
50ºC
24 16
# of Carbons
20 28
Biochemistry: Lipids p. 20 of 26

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Almost always esterified or otherwise derivatized
Most common esterification is to glycerol
Note that glycerol is achiral but its derivatives are often chiral
Triacylglycerols; all three OHs on glycerol are esterified to fatty acids
Phospholipids: 3-OH esterified to phosphate or a phosphate derivative glycerol
Biochemistry: Lipids p. 21 of 26

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Neutral lipids
R
1,2,3 all aliphatic
Mixture of saturated & unsaturated; unsaturated more than half
Energy-storage molecules
Yield >2x energy/gram as proteins or carbohydrates, independent of the waterstorage issue …
Lipids are stored anhydrously; carbohydrates & proteins aren’t
Biochemistry: Lipids p. 22 of 26

 Lipases break these molecules down by hydrolyzing the 3-O esters and 1-O esters
 Occurs in presence of bile salts
(amphipathic derivatives of cholesterol)
 These are stored in fat droplets within cells, including specialized cells called adipocytes
Biochemistry: Lipids p. 23 of 26

 Also called phosphoglycerides
 Primary lipid constituents of membranes in most organisms
 Simplest: phosphatides
(3’phosphoesters)
 Of greater significance: compounds in which phosphate is esterified both to glycerol and to something else with an
—OH group on it
Biochemistry: Lipids p. 24 of 26

 Generally categorized first by the polar “head” group; secondarily by fatty acyl chains
 Usually C-1 fatty acid is saturated
 C-2 fatty acid is unsaturated
 Think about structural consequences!
Biochemistry: Lipids p. 25 of 26

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Variation on other phosphoester position
Ethanolamine ( R
1-4
(CH
2
)
2
—NH
3
+ )
= H) ( —O—
Serine ( R
4
( —O—CH
2
= COO )
-CH-(COO ) —NH
3
+ )
Methyl, dimethylethanolamine
( —O—(CH
2
)
2
—NH m
+ (CH
3
)
2m
)
Choline (
(CH
2
)
2
R
4
=H, R
—N(CH
3
)
3
+
1-3
)
=CH
3
) ( —O—
Glucose, glycerol . . .
Biochemistry: Lipids p. 26 of 26