Chapter 27. Biomolecules: Lipids Why this Chapter? Lipids are the largest and most diverse class of...
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Transcript of Chapter 27. Biomolecules: Lipids Why this Chapter? Lipids are the largest and most diverse class of...
Chapter 27. Chapter 27. Biomolecules: LipidsBiomolecules: Lipids
Why this Chapter?Why this Chapter?
Lipids are the largest and most diverse class of biomolecules
To examine lipid structure, function, and metabolism
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About LipidsAbout Lipids
Natural materials that preferentially extract into nonpolar organic solvents
Includes fats, oils, waxes, some vitamins and hormones, some components of membrane
General types: esters (“saponifiable”) and those that can’t be hydrolyzed
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27.1 Waxes, Fats, and Oils27.1 Waxes, Fats, and Oils
Waxes - contain esters formed from long-chain (C16-C36) carboxylic acids and long-chain alcohols (C24-C36)
Triacontyl hexadecanoate is in beeswax
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TriacylglycerolTriacylglycerolTri-esters of glycerol with three
long-chain carboxylic acids, fatty acids.
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Fatty Acids (from Fats and Oils)Fatty Acids (from Fats and Oils)
Straight-chain (C12 - C20) carboxylic acidsDouble bonds are cis-substituted but trans-
fatty acids also occurA fat or oil in nature occurs as a mixture of
many different triacylglycerolsThe most abundant saturated fatty acids are
palmitic (C16) and stearic (C18)
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Unsaturated and Polyunsaturated Unsaturated and Polyunsaturated Fatty AcidsFatty Acids
Oleic (C18 with one C=C) and linolenic (C18 with 3 C=C) are the most abundant unsaturated
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27.2 Soap27.2 Soap
A mixture of sodium or potassium salts of long-chain fatty acids produced by alkaline hydrolysis (saponification) of animal fat with alkali
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Cleansing Action of SoapCleansing Action of Soap
The carboxylate end of the long-chain molecule is ionic and therefore is preferentially dissolved in water
The hydrocarbon tail is nonpolar and dissolves in grease and oil
Soaps enable grease to be dissolved into water
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DetergentsDetergents
“Hard” water contains Mg+2 and Ca+2 that form insoluble salts with soaps
Synthetic detergents are alkylbenzene sulfonates that dissolve dirt like soaps but do not form scums with Mg+2 and Ca+2 .
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27.3 Phospholipids27.3 Phospholipids
Phospholipids are diesters of H3PO4, phosphoric acid
Phosphoric acid can form monoesters, diesters and triesters
In general these are known as “phosphates”
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PhosphoglyceridesPhosphoglyceridesContain a glycerol backbone linked by ester
bonds to two fatty acids and phosphoric acidFatty acid residues with C12–C20The phosphate group at C3 has an ester link to
an amino alcohol
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SphingolipidsSphingolipidsThe other major group of phospholipids Sphingosine or a dihydroxyamine backbone Constituents of plant and animal cell membranesAbundant in brain and nerve tissue, as coating
around nerve fibers.
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Phosphoglyceride MembranesPhosphoglyceride MembranesPhosphoglycerides comprise the major lipid
component of cell membranesNonpolar tails aggregate in the center of a bilayer Ionic head is exposed to solvent
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27.4 Prostaglandins & Other Eicosanoids27.4 Prostaglandins & Other Eicosanoids
C20 lipids that contain a five-membered ring with two long side chains
Present in small amounts in all body tissues and fluids
Many physiological effects
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Prostaglandin SourcesProstaglandin SourcesBiosynthesized from arachidonic acid (C20
unsaturated fatty acid)
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27.5 Terpenoids27.5 TerpenoidsSteam distillation of plant extracts produces
“essential oils” Chemically related to compounds in turpentine
(from pine sap) called terpenes and thus called terpenoids
Mostly hydrocarbons (some oxygens) that do not contain esters (stable to hydrolysis)
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Biosynthesis of TerpenoidsBiosynthesis of Terpenoids Isopentenyl pyrophosphate (IPP) forms higher
isoprenoids in reactions catalyzed by prenyl transferase
Monoterpenoids, diterpenoids, and tetraterpoids arise from 1-deoxyxylulose 5-phosphate (DXP).
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Mevalonate Pathway to Mevalonate Pathway to Isopentenyl DiphosphateIsopentenyl Diphosphate
Begins with the conversion of acetate to acetyl CoA followed by Claisen condensation to yield acetoacetyl CoA
Catalyzed by acetoacetyl-CoA acetyltransferase
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Aldol CondensationAldol Condensation Carbonyl condensation reaction of acetoacetyl CoA with
acetyl CoA Produces 3-hydroxy-3-methylglutaryl CoA (HMG-CoA)
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Phosphorylation & DecarboxylationPhosphorylation & DecarboxylationPyrophosphorylation gives mevalonyl-PPAddition of phosphate from ATP followed by
loss of CO2 and phosphate
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Conversion of Isopentenyl Diphosphate Conversion of Isopentenyl Diphosphate to Terpenoidsto Terpenoids
For triterpenes and larger, head-to-head coupling of farnesyl diphosphates gives squalene
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Mechanism of IsomerizationMechanism of Isomerization
Isomerization of IPP to DMAPP is catalyzed by IPP isomerase through a carbocation pathway
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Coupling MechanismCoupling MechanismNucleophilic substitution reaction in which the
double bond of IPP behaves as a nucleophile in displacing diphosphate ion leaving group (PPO)
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Conversions of MonoterpenoidsConversions of MonoterpenoidsTypically involves carbocation intermediates
and multistep reaction pathways catalyzed by a terpene cyclase
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27.6 Steroids27.6 SteroidsSteroids,are another class of nonsaponifiable lipid,
defined by structureHas four fused rings A, B, C, and D, beginning at the
lower leftCarbon atoms are numbered beginning in the A ringThe six-membered rings are in fixed chair
conformations
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Functions of SteroidsFunctions of Steroids
In humans as hormones, steroids are chemical messengers secreted by glands and carried through the bloodstream to target tissues
Also widely distributed as cholesterol
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Male Sex HormonesMale Sex HormonesTestosterone and androsterone are the two most
important male sex hormones, or androgensAndrostanedione is a precursor
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Female Sex HormonesFemale Sex HormonesEstrone and estradiol are the two most
important female sex hormones, or estrogensProgesterone is the most important progestin,
steroids that function in pregnancy
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Adrenocortical HormonesAdrenocortical HormonesAdrenocortical steroids: secreted by the adrenal
glands near the upper end of each kidneyMineralocorticoids: control tissue swelling by
regulating cellular salt balance Glucocorticoids: regulation of glucose
metabolism and in the control of inflammation
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Synthetic SteroidsSynthetic SteroidsMade in pharmaceutical laboratories as new
drugs Includes oral contraceptives and anabolic agentsMethandrostenolone is an anabolic steroid used
for tissue-building
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27.7 Steroid Biosynthesis27.7 Steroid Biosynthesis
Enzyme-catalyzed addition of oxygen atom to squalene
Stereospecific formation of an oxirane from an alkene
1. x
2. x
3. x4. None of these is
commonly found in nature.
5. All of these are commonly found in nature.
Which fatty acid is Which fatty acid is notnot commonly commonly found in nature?found in nature?
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20% 20% 20%20%20%
1. 1
2. 2
3. 34. All of these are
lipids. 5. None of these are
lipids.
Which of the following would not be Which of the following would not be classified as a lipid?classified as a lipid?
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20% 20% 20%20%20%
Which of the following describes how a soap Which of the following describes how a soap cleans?cleans?
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1. The fatty acids react with grease molecules to form water soluble compounds that are subsequently washed away.
2. The fatty acids form micelles which encapsulate grease molecules. These micelles are soluble in water and consequently washed away.
3. The fatty acids react with grease molecules to generate new compounds that can form micelles in water. These micelles are soluble in water and consequently washed away.
4. All of these statements accurately describe how soap works.
5. None of these statements accurately describe how soap works.
The following molecule would The following molecule would be expected to form micelles.be expected to form micelles.
1 2
50%50%
1. True2. False
What forces are responsible for lipid What forces are responsible for lipid bilayer and micelle formation?bilayer and micelle formation?
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20% 20% 20%20%20%
1. covalent bonding and electrostatic interactions
2. hydrophobic effects and hydrogen bonding
3. electrostatic interactions and hydrophobic effects
4. electrostatic interactions and fluid mosaics
5. hydrophobic effects and fluid mosaics
The figure shown is:The figure shown is:
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20% 20% 20%20%20%
1. phosphatidylethanolamine
2. phosphatidylcholine3. phosphatidylserine4. sphingosine5. sphingomyelin
What do these two lipids have in What do these two lipids have in common?common?
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1. They are eicosanoids.
2. They form micelles in water.
3. They are prostaglandins.
4. They are steroids.5. They are used as
detergents.
Which is a role of the Which is a role of the prostaglandins?prostaglandins?
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20% 20% 20%20%20%1. They stimulate the contraction of uterine muscle.
2. They lower blood pressure in the blood stream.
3. They suppress gastric ulceration.
4. All of these5. None of these
The molecule shown below is a:The molecule shown below is a:
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1. thromboxane2. prostaglandin3. leukotriene4. eicosanoid5. thromboxane and
eicosanoid
The molecule shown below is:The molecule shown below is:
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1. lanosterol2. camphor3. β-carotene4. patchouli alcohol5. None of these
The first step of mevalonate The first step of mevalonate synthesis, shown below, is a:synthesis, shown below, is a:
The 1The 1stst step of mevalonate synthesis, step of mevalonate synthesis, shown is a:shown is a:
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1. Claisen condensation2. aldol-like
condensation3. reduction reaction4. substitution reaction5. Schiff base formation
Why can the molecule below Why can the molecule below notnot be be classified as a steroid?classified as a steroid?
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1. Steroids cannot have double bonds.
2. Steroids cannot contain branched hydrocarbon chains.
3. Steroids have a different arrangement of rings.
4. Steroids are usually comprised of benzene rings, making them mostly flat.
5. All of these
How is cholesterol transported How is cholesterol transported through the blood stream?through the blood stream?
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1. through micelles2. through ion
channels3. by prostaglandins4. by lipoproteins5. as water solvated
ions
In which organ of the body is In which organ of the body is cholesterol synthesized?cholesterol synthesized?
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1. the lungs2. the gallbladder3. the liver4. the kidneys5. the pancreas
Which of the following is Which of the following is notnot a a good indicator of health?good indicator of health?
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1. cholesterol levels below 200 mg/dL
2. LDL levels greater than 100 mg/dL
3. HDL levels greater than 60 mg/dL
4. active, athletic lifestyle
5. diets rich in seafood