Chapter 21: Lipids
Chapter 21: Lipids
Triglyceride: A triester of glycerol with three fatty acids.• Hydrophobic (most of the molecule is non-polar)
• Two or three different fatty acid components are present
The Fatty acids:• Are unbranched carboxylic acids• 10 to 20 carbons long, even number of carbons• Cis-isomer
Chapter 21: Lipids
Hardening: The reduction of some or all of the carbon-carbon double bonds of an unsaturated triglyceride using H2/transition metal catalyst, which converts a liquid triglyceride to a semisolid.• In practice, the degree of hardening is carefully controlled to
produce fats of a desired consistency.• The resulting fats are sold for kitchen use (Crisco, Spry, Dexo,
and others).• Margarine and other butter substitutes are produced by partial
hydrogenation of polyunsaturated oils derived from corn, cottonseed, peanut, and soybean oils.
• The hardening process is the source of trans fatty acids
Chapter 21: Lipids
Saponification: the base-promoted hydrolysis of fats and oils in aqueous NaOH and produces glycerol and a mixture of fatty acid salts called soaps.
O
CH2OCR
CH2OCR
RCOCH
O
O
CH2OH
CH2OH
HOCH RCO-Na+
O
A triglyceride 1,2,3-Propanetriol(Glycerol, glycerin)
+
Sodium soaps
3saponification
Chapter 21: Lipids
Phospholipids and Glycolipids
Chapter 21: Lipids
Complex lipids form the membranes around cells and around small structures within cells.In aqueous solution, complex lipids spontaneously form into a lipid bilayer, with a back-to-back arrangement of lipid monolayers.• Polar (hydrophilic) head groups are in contact with the aqueous
environment.• Nonpolar (hydrophobic) tails are buried within the bilayer and
shielded from the aqueous environment.• The major force driving the formation of lipid bilayers is
hydrophobic interaction.• The arrangement of hydrocarbon tails in the interior can be rigid
(if rich in saturated fatty acids) or fluid (if rich in unsaturated fatty acids).
Chapter 21: Lipids
Chapter 21: Lipids
Glycerolphospholipids
X = AlcoholR1 = Fatty acid tail (saturated or unsaturated)R2 = Fatty acid tail (this one is always unsaturated)
Chapter 21: Lipids
X = Choline
If the other alcohol is choline, the glycerophospholipid is called a phosphatidylcholine (common name lecithin).
Chapter 21: Lipids
X = ethanolamine or serine
If the other alcohol is ethanolamine or serine, the glycerophospholipid is called a cephalin.
Chapter 21: Lipids
Sphingolipids: Contain sphingosine instead of glycerol, from which this class of compounds in named. The sphingolipid myelin is found in the coatings of nerve axons.
OH
(CH2)12CH3
HO
NH2
SphingosineOH
(CH2)12CH3
HO
NHCR
A ceramide(an N-acylsphingosine)
OPOCH2CH2N(CH3)3
(CH2)12CH3
HO
NHCR
A sphingomyelinO
O-+
O O
Chapter 21: Lipids
GlycolipidGlycolipid:: a complex lipid that contains carbohydrates and ceramides.• The carbohydrate is either glucose or galactose.• The cerebrosides are ceramide mono- or oligosaccharides.• The following is a glucocerebroside.
O
(CH2)12CH3
HO
NHCR
O
H
HO
H
HO
H
HOH
H
OHO
a-glycosidic bond
a unit of -D-glucopyranose
a ceramide
Chapter 21: Lipids
Steroids: A group of plant and animal lipids that contain this tetracyclic ring structure
A B
C D
Cholesterol is the most abundant steroid in the human body, and also the most important.• It is a component in plasma membranes in all animal cells.• It is the precursor of all steroid hormones and bile acids.
HO
Chapter 21: Lipids
21-15
Steroid Hormones• Male sex hormonesMale sex hormones• Synthesized in the testes from cholesterol.• Responsible for the development of male secondary
sex characteristics.
AndrosteroneTestosteroneO
OH
H3C
H3C H3C
H3C
O
HO
21-16
Steroid HormonesAmong the synthetic anabolic steroids are:
O
H3C
H3C
MethandienoneO
CH3
H3CH3C
OHOH
CH3
MethenoloneO
H3C
H3CO
4-Androstene-3,17-dione
21-17
Steroid HormonesFemale sex hormones• Synthesized in the ovaries from progesterone.• Responsible for the development of female secondary
sex characteristics and control of the menstrual cycle.
Progesterone Estradiol
H3C
H3C
C=O
O
CH3OH
HO
H3Cseveralsteps
21-18
Steroid Hormones• Progesterone-like analogs are used in oral
contraceptives:
H3C
O
OHC CH
H3C
O
OHC CCH3
NH3C
CH3
"Nor" refers tothe absence of a methyl group here
Norethindrone
Mifepristone(RU486)
21-19
Glucocorticoid Hormones• Glucocorticoid hormonesGlucocorticoid hormones• Synthesized in the adrenal cortex.• Regulate metabolism of carbohydrates.• Decrease inflammation.• Involved in the reaction to stress.
Aldosterone
C=O
CH2OH
O
H
H3C H
H
CHHO
O
21-20
Bile SaltsBile saltsBile salts are oxidation products of cholesterol.• Synthesized in the liver, stored in the gallbladder, and
secreted into the intestine where they emulsify dietary fats and aid in their absorption and digestion.
HO
H3C
CH3
H3C
OH
HO NH
O
HO
H3C
CH3
H3C
OH
HO NH
O
SO32-
Glycocholate(from glycine)
Taurocholate(from taurine)
COO-
Chapter 21: Lipids
Lipoproteins: Lipoproteins: Carriers of cholesterol.
Chapter 21: Lipids
LipoproteinsLipoproteins
Chapter 21: Lipids
•Chylomicrons carry triglycerides (fat) from the intestines to the liver, skeletal muscle, and to adipose tissue.•Very low density lipoproteins (VLDL) carry (newly synthesised) triacylglycerol from the liver to adipose tissue.•Intermediate density lipoproteins (IDL) are intermediate between VLDL and LDL. They are not usually detectable in the blood.•Low density lipoproteins (LDL) carry cholesterol from the liver to cells of the body. LDLs are sometimes referred to as the "bad cholesterol" lipoprotein.•High density lipoproteins (HDL) collect cholesterol from the body's tissues, and bring it back to the liver. HDLs are sometimes referred to as the "good cholesterol" lipoprotein.
Chapter 21: Lipids
• LDL Normal plasma levels are 175 mg/100 mL.• If there are sufficient LDL receptors on the surface of cells, LDL is removed from circulation and its concentration in blood plasma drops.• In the disease called famelial hypercholesterolemia, there are not enough LDL receptors and plasma levels of cholesterol may be as high as 680 mg/100 mL.• The commonly used statin drugs inhibit the synthesis of cholesterol by blocking HMG-CoA reductase
LDL:LDL: