Diapositiva 1

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UNIT 5. LIPIDS
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OUTLINE
5.1. Introduction. 5.2. Fatty acids. 5.3.
Eicosanoids. 5.4. Triacylglycerols
Triglycerides. 5.5. Waxes. 5.6. Membrane lipids
glycerophospholipids and sphingolipids. 5.7.
Isoprenoids (and steroids) 5.8. Lipoproteins.
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• 5.1. INTRODUCTION

• Organic molecules highly hydrophobic and water
  insoluble.
• Biological roles
• - Energy reserve (i.e. triacylglicerols).
• - Structural component of the biological
  membranes
• (i.e. phospholipids).
• - Protection (i.e. wax).
• - Biochemical signals, cofactor or pigments
• Lipid Classification
• - Fatty acids. - Phospholipids.
• - Eicosanoids. - Sphingolipids.
• - Triacylglicerols. - Isoprenoids.
• - Waxes. - Conjugated lipids.

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• 5.2. FATTY ACIDS

• Carboxylic acids with long-chain hydrocarbon
  side groups.
• They can be branched and saturated, unsaturated
  or polyunsaturated (contain two or more double
  bonds).
• The double bonds tend to occur at every third
  carbon atom (not conjugated).
• Ionizated at physiological pH.
• Usually, they are in the free, uncomplexed state.

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• 5.2. FATTY ACIDS

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• 5.2. FATTY ACIDS

• Fatty acid double bonds almost always have the
  cis configuration.

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• 5.2. FATTY ACIDS

• Properties
• ? Higher unsaturated grade higher fluidity.
• ? Higher unsaturated grade (same chain length)
  lower melting point.

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• 5.3. EICOSANOIDS

• They are derived from arachidonic acid,
  204(?5,8,11,14).
• Types
• ? Prostaglandins (they act as local hormones)
  they are involved in
• - The production of pain and fever
• - Inflammation processes
• - Increase of the body temperature
• - Regulation of blood pressure and blood
  coagulation.
• - Control of the Ionic transport.
• - Dream induction

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• 5.3. EICOSANOIDS

? Thromboxanes (found within platelets)
Stimulate vasoconstriction and platelet
aggregation. ? Leukotrienes (present within
leukocytes) Involved in - Oedema
production. - Vasoconstriction. - Bronchi
constriction - Anaphylactic processes.
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• 5.4. TRIACYLGLICEROLS

• Glycerol esterified with three fatty acids.
  Monoacylglicerols and diacylglicerols are
  metabolic intermediates.
• Major energy reserve (stored in anhydrous form).
• Types
• Simple triacylglicerols (i.e.
  tristearoylglycerol( tristearin)
  trioleoylglycerol (triolein).
• Mixed triacylglicerols (i.e. 1-stearoyl,
  2-linoleoyl, 3-palmitoyl glycerol).
• Highly hydrophobic.
• Adipocytes and adipose tissue.
• Thermal insulation (important for warm-blooded
  aquatic animals).

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• 5.4. TRIACYLGLICEROLS

• Provide about six times the metabolic energy of
  an equal weight of hydrated glycogen.
• They are hydrolysed by lipases or alkali
  (saponification)

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• 5.5. WAXES

• Esters of long-chain monohydroxylic alcohols
  (16-30 C) with long-chain fatty acids (14-36 C)
  (saturated or unsaturated)
• Properties
• - Energy reserve (plancton).
• - Water-repellant surfaces (i.e. animals skin,
  leaves of certain plants, bird feathers).
• - Highly hydrophobic.
• - Several industrial uses (lotions, cosmetics,
  etc.).

Triacontanylpalmitate, major component of the bee
wax.
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• 5.6. MEMBRANE LIPIDS

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• 5.6. MEMBRANE LIPIDS GLYCEROPHOSPHOLIPIDS

• 1,2-diacylglycerol that has a phosphate group
  esterified at the carbon atom 3 of the glycerol
  backbone. The phosphate group is linked to a
  highly polar or charged group (X).
• Usually they contain a saturated fatty acid (C16
  or C18)C1-linked and an unsaturated fatty acid
  (C16-C20) C2-linked.
• Amphipathic molecules.
• They are derived from phosphatidic acid.

Glycerophopholipids backbone structure
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• 5.6. MEMBRANE LIPIDS GLYCEROPHOSPHOLIPIDS

Phosphatidylcholine
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• 5.6. MEMBRANE LIPIDS GLYCEROPHOSPHOLIPIDS

• Some phospholipids contain an alkyl group ether
  linked.

Plasmalogen (heart muscle)
Platelet activating factor major mediator of
hypersensivity, acute inflammatory reactions,
allergic responses and anaphylactic shock.
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• 5.6. MEMBRANE LIPIDS SPHINGOLIPIDS

• One polar group and to unpolar chains (glycerol
  is not present)
• They contain the amino alcohol sphingosine, one
  fatty acid (long chain) and a polar group
  (alcohol or sugar)

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• 5.6. MEMBRANE LIPIDS SPHINGOLIPIDS

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• 5.6. MEMBRANE LIPIDS SPHINGOLIPIDS

• Cerebrosides and globosides (ceramide
  oligosaccharides) are neutral glycolipids.
  Gangliosides contain N-acetylneuraminic acid
  (sialic acid), with negative charge at pH 7.

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• 5.6. MEMBRANE LIPIDS SPHINGOLIPIDS

• The carbohydrate present in several
  sphingolipids define the human being blood groups
  ( A, B and 0).

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• 5.7. ISOPRENOIDS

• They contain isoprene units (5 C).

• They precursor for the synthesis is
  isopentenylpyrophosphate .
• The isoprenoids are grouped into terpenes and
  steriods.

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• 5.7. ISOPRENOIDS TERPENES

• Classification in the base of the number of
  isoprene units

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• 5.7. ISOPRENOIDS TERPENES

• Linear or cyclic structures.
• Present in plants, fungi and bacteria.
• Pigments, molecular signalling (hormones and
  pheromones) and defence agents.
• Plant oils belong to this groups (aromas and
  flavours).
• They are precursor for fat-soluble vitamins
  synthesis.

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• 5.7. ISOPRENOIDS TERPENES

• Fat-soluble vitamins they cannot be synthesised
  by human beings (diet).
• They are dissolved as fats and oils.
• Vitamin A (retinol)
• - Hormone and main pigment involved in vision.
• - It is a carotenoid.
• Vitamin D
• - It is derived from cholesterol.
• - It increases the concentration of Ca2 in
  physiological serum
• Vitamin E (tocopherols)
• - Biological antioxidant, It avoid food
  degradation.
• - Prevent oxidation of the membrane lipids.

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• 5.7. ISOPRENOIDS TERPENES

Vitamin K - Blood clotting. Ubiquinones and
plastoquinones - Lipophilic electron
transporters (redox reactions).
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• 5.7. ISOPRENOIDS STERIODS

• Membrane lipids in eukaryotic cells.
• They are derived from triterpenes containing 4
  rings phenathrene nucleus (3 rings containing 6
  C), and a pentane ring (5 C) Cyclopentanoperhydro
  phenanthrene.
• They are classified on the base of the number
  and position of the double bonds, location of the
  radicals, etc.

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• 5.7. ISOPRENOIDS STERIODS

Cholesterol Main steriod in animals (cellular
membranes) It is amphipathic. It is the precursor
in the synthesis of many steriods such as
hormones, vitamin D, bile acids
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• 5.7. ISOPRENOIDS STERIODS

Bile acids they act as detergents in gut. They
are more soluble than cholesterol. Steroid
hormones they promote metabolism and gene
expression changes. Types - Glucocorticoids
i.e cortisol involved in proteins, lipids and
carbohydrates metabolism. - Aldosterone and
mineralocorticoids, they regulate water and salt
excretion (kidneys). - Androgens and estrogens
sexual development.
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• 5.7. ISOPRENOIDS STERIODS

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• 5.8. LIPOPROTEINS

• Molecular complexes in blood plasma of mammals.
• They facilitate lipids transfer between tissues
  (triacylglycerols, phospholipids and
  cholesterol).
• Apolipoproteins or apoproteins are synthesised
  in the liver.
• They have different density and lipids/proteins
  ratio.

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• 5.8. LIPOPROTEINS

- Chylomicrons extremely low density. They
transport triacylglycerols and cholesterol esters
(food) from gut to adipose tissue and muscles. -
Very-low-density lipoproteins (VLDL) they
transfer lipids (triacylglycerols) to the
tissues to be used for energy. - Low-density
lipoproteins (LDL) they transport cholesterol
and its esters to the tissues. - High-density
lipoproteins (HDL) Rich in cholesterol but poor
in triacyglycerol (they promote the excretion of
the excess of cholesterol).
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• 5.8. LIPOPROTEINS