Lipids

1

• Lipids

Chapter 26
2
Lipids

• Lipids A heterogeneous class of naturally
  occurring organic compounds classified together
  on the basis of common solubility properties.
• They are insoluble in water but soluble in
  aprotic organic solvents, including diethyl
  ether, methylene chloride, and acetone.
• Lipids include
• triglycerides, phospholipids, prostaglandins,
  prostacyclins, and fat-soluble vitamins.
• cholesterol, steroid hormones, and bile acids.

3
Triglycerides

• Triglyceride An ester of glycerol with three
  fatty acids.

Saponification
4
Fatty Acids

• Fatty acid A carboxylic acid derived from
  hydrolysis of animal fats, vegetable oils, or
  membrane phospholipids.
• Nearly all have an even number of carbon atoms,
  most between 12 and 20, in an unbranched chain.
• The three most abundant are palmitic (160),
  stearic (180), and oleic acid (181), where the
  first number is the number of carbons and the
  second is the number of double bonds in the
  hydrocarbon chain.
• In most unsaturated fatty acids, the cis isomer
  predominates the trans isomer is rare.
• Unsaturated fatty acids have lower melting points
  than their saturated counterparts the greater
  the degree of unsaturation, the lower the melting
  point.

5
Fatty Acids

• The most common fatty acids.

Higher mp
Lower mp
6
Triglycerides

• Physical properties depend on the fatty acid
  components.
• Melting point increases as the number of carbons
  in its hydrocarbon chains increases and as the
  number of double bonds decreases.
• Oils Triglycerides rich in unsaturated fatty
  acids are generally liquid at room.
• Fats Triglycerides rich in saturated fatty acids
  are generally semisolids or solids at room
  temperature.

7
Triglycerides

• example a triglyceride derived from one molecule
  each of palmitic acid, oleic acid, and stearic
  acid, the three most abundant fatty acids in the
  biological world.

8
Triglycerides

• The lower melting points of triglycerides rich in
  unsaturated fatty acids are related to
  differences in their three-dimensional shape.
• Hydrocarbon chains of saturated fatty acids can
  lie parallel with strong dispersion forces
  between their chains they pack into
  well-ordered, compact crystalline forms and melt
  above room temperature.
• Because of the cis configuration of the double
  bonds in unsaturated fatty acids, their
  hydrocarbon chains have a less ordered structure
  and dispersion forces between them are weaker
  these triglycerides have melting points below
  room temperature.

9
Soaps and Detergents

• Natural soaps are prepared by boiling lard or
  other animal fat with NaOH, in a reaction called
  saponification (Latin, sapo, soap).

10
Soaps and Detergents

• Soaps clean by acting as emulsifying agents
• Their long hydrophobic hydrocarbon chains are
  insoluble in water and tend to cluster in such a
  way as to minimize their contact with water.
• Their polar hydrophilic carboxylate groups, on
  the other hand, tend to remain in contact with
  the surrounding water molecules.
• Driven by these two forces, soap molecules
  spontaneously cluster into micelles.

11
Soaps and Detergents

• A soap micelle nonpolar (hydrophobic)
  hydrocarbon chains cluster in the inside and
  polar (hydrophilic) carboxylate groups lie on the
  surface.

12
Soaps and Detergents

• micelle A spherical arrangement of organic
  molecules in water clustered so that their
  hydrophobic parts are buried inside the sphere
  and their hydrophilic parts are on the surface of
  the sphere and in contact with water.
• when soap is mixed with water-insoluble grease,
  oil, and fats, the nonpolar parts of the soap
  micelles dissolve these nonpolar dirt molecules
  and they are carried away in the polar wash water.

13
Soaps and Detergents

• Soaps form water-insoluble salts when used in
  water containing Ca(II), Mg(II), and Fe(III) ions
  (hard water).

14
Synthetic Detergents

• The design criteria for a good detergent are
• a long hydrocarbon tail of 12 to 20 carbons.
• a polar head group that does not form insoluble
  salts with Ca(II), Mg(II), or Fe(III) ions.
• The most widely used synthetic detergents are the
  linear alkylbenzenesulfonates (LAS).

15
Synthetic Detergents

• Also added to detergent preparations are
• foam stabilizers.
• bleaches.
• optical brighteners.

16
Prostaglandins

• Prostaglandins A family of compounds that have
  the 20-carbon skeleton of prostanoic acid.

17
Prostaglandins, origin

• Prostaglandins are not stored in tissues as such,
  but are synthesized from membrane-bound 20-carbon
  polyunsaturated fatty acids in response to
  specific physiological triggers.
• One such polyunsaturated fatty acid is
  arachidonic acid (notice the all cis
  configurations).

18
Prostaglandins, examples

• Among the prostaglandins synthesized
  biochemically from arachidonic acid are

PGE2 generated in macrophages of the liver and
lungs triggers the earliest phase of fever
following any infection
19
Prostaglandins

• Research on the involvement of PGs in
  reproductive physiology has produced several
  clinically useful derivatives.
• (15S)-15-methyl-PGF2? is used as a therapeutic
  abortifacient.

20
Prostaglandins

• The PGE1 analog, misoprostol, is used to prevent
  the ulceration associated with the use of aspirin.

21
Eicosanoids

• The prostaglandins are members of an even larger
  family of compounds called eicosanoids, all of
  which contain 20 carbons and are derived from
  polyunsaturated fatty acids.

22
Eicosanoids

• Leukotrienes are found primarily in white blood
  cells.
• One function is constriction of smooth muscles,
  especially those of the lungs.

23
Steroids

• Steroids A group of plant and animal lipids that
  have this tetracyclic ring structure.
• The features common to the ring system of most
  naturally occurring steroids are illustrated next.

24
Steroids

• The fusion of rings is trans and each atom or
  group at a ring junction is axial.
• The pattern of atoms or groups along the ring
  junctions is nearly always trans-anti-trans-anti-t
  rans.
• The steroid system is nearly flat and quite
  rigid.
• Most have have axial methyl groups at C-10 and
  C-13.

25
Cholesterol
26
Androgens

• Androgens - male sex hormones.

27
Synthetic Anabolic Steroids

• A way to increase the testosterone concentration
  is to use a prohormone, which the body converts
  to testosterone for example andro.

28
Available on the internet, dangerous

• Generic Name methandrostenoloneDanabol /
  Dianabol has always been one of the most popular
  anabolic steroids available. Danabol / Dianabol's
  popularity stems from it's almost immediate and
  very strong anabolic effects. 4-5 tablets a day
  is enough to give almost anybody dramatic
  results. It is usually stacked with deca
  durabolin and testosterone enanthate. Along with
  strong anabolic effects comes the usual androgen
  side effects, users often report an overall sense
  of well being. Danabol / Dianabol is a strong
  anabolic and androgenic product. It most often
  produced dramatic gains in size and strength.
  Danabol / Dianabol was also shown to increase
  endurance and glycogen retention.
• The down side is that this drug is responsible
  for a number of side effects. It is an alpha
  alkylated 17 compound, which is quite toxic to
  the liver. Average dosages for Danabol / Dianabol
  have been in the range of 15mg to 30mg a day oral
  or 50mg to 100mg a week by injection. Regarded by
  many athletes as being one of the most effective
  oral steroids ever produced. It was not known as
  the "Breakfast of Champions" for nothing. Danabol
  / Dianabol is still one of the most effective
  strength and size building oral steroids probably
  second only to Anadrol 50 but it is not as harsh
  on the system as Anadrol 50 is.

29
Estrogens

• Estrogens - female sex hormones.

30
Synthetic Estrogens

• Progesterone-like analogs are used in oral
  contraceptives.

31
Glucorticoid Hormones

• Synthesized in the adrenal cortex.
• Regulate metabolism of carbohydrates.
• Decrease inflammation.
• Involved in the reaction to stress.

32
Mineralocorticoid Hormones

• Synthesized in the adrenal cortex.
• Regulate blood pressure and volume by stimulating
  the kidneys to absorb Na, Cl-, and HCO3-.

33
Bile Acids

• Synthesized in the liver, stored in the
  gallbladder, and secreted into the intestine
  where their function is emulsify dietary fats and
  aid in their absorption and digestion.

34
Biosynthesis of Steroids

• The building block from which all carbon atoms of
  steroids are derived is the two carbon acetyl
  group of acetyl-CoA
• Stage 1 synthesis of isopentenyl pyrophosphate
  from three molecules of acetyl-CoA.
• Stage 2 synthesis of cholesterol.
• Stage 3 conversion of cholesterol to other
  steroids.

35
Vitamin E
36
Phospholipids

• Phospholipids are the second most abundant group
  of naturally occurring lipids.
• They are found almost exclusively in plant and
  animal membranes, which typically consist of 40
  -50 phospholipids and 50 - 60 proteins.
• The most abundant phospholipids are esters of
  phosphatidic acid (glycerol esterified with two
  molecules of fatty acid and one of phosphoric
  acid).
• The three most abundant fatty acids in
  phosphatidic acids are palmitic acid (160),
  stearic acid (180), and oleic acid (181).

37
Phosphatidic acids, an example

• A phosphatidic acid
• Further esterification with a low-molecular
  weight alcohol gives a phospholipid.

38
Phospholipids

• Among the most common of these low-molecular-weigh
  t alcohols are

39
Phospholipids, an example

• A lecithin
• In aqueous solution, phospholipids spontaneously
  form into a lipid bilayer, with a back-to-back
  arrangement of lipid monolayers.

40
Biological Membranes

• Fluid mosaic model A biological membrane
  consists of a phospholipid bilayer with proteins,
  carbohydrates, and other lipids embedded on the
  surface and in the bilayer.
• fluid Signifies that the protein components of
  membranes float in the bilayer and can move
  freely along the plane of the membrane.
• mosaic Signifies that the various components of
  the membrane exist side by side, as discrete
  units rather than combining to form new molecules
  and ions.

41
Biological Membranes

• Fluid-mosaic model of a biological membrane
  showing the lipid bilayer and membrane proteins
  on the inner and outer surfaces of the membrane
  and penetrating the thickness of the membrane.

42
Fat-Soluble Vitamins

• Vitamins are divided into two broad classes on
  the basis of their solubility
• Those that are fat soluble, and hence classified
  as lipids.
• Those that are water soluble.
• The fat-soluble vitamins include A, D, E, and K.

43
Vitamin A

• Occurs only in the animal world.
• Found in the plant world in the form of a
  provitamin in a group of pigments called
  carotenes.

44
Vitamin A

• The best understood role of Vitamin A is its
  participation in the visual cycle in rod cells.
• the active molecule is retinal (vitamin A
  aldehyde), which forms an imine with an -NH2
  group of the protein opsin to form the visual
  pigment called rhodopsin.
• the primary chemical event of vision in rod cells
  is absorption of light by rhodopsin followed by
  isomerization of the 11-cis double bond to the
  11-trans configuration.

45
Vitamin A and the Chemistry of Vision
46
Vitamin A and the Chemistry of Vision

• The primary chemical reaction of vision is
  absorption of light by rhodopsin.

47
Vitamin D

• A group of structurally related compounds that
  play a role in the regulation of calcium and
  phosphorus metabolism.
• The most abundant form in the circulatory system
  is vitamin D3.

48
Vitamin E

• Vitamin E is a group of compounds of similar
  structure, the most active of which is
  ?-tocopherol.
• In the body, vitamin E functions as an
  antioxidant it traps peroxy radicals of the type
  HOO and ROO formed as a result of oxidation by
  O2 of unsaturated hydrocarbon chains in membrane
  phospholipids.

49
Vitamin K

• The name of this vitamin comes from the German
  word Koagulation, signifying its important role
  in the blood-clotting process.