Introduction to Lipids

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Introduction to Lipids
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What are Lipids ??

• Lipids are organic compounds which are related to
  fatty acids
• Lipids are insoluble in water soluble in
  nonpolar solvents (fat solvents) such as alcohol,
  ether, benzene, acetone, chloroform

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classification of lipids
Derived Lipids
Simple Lipids
Conjugated Lipids

• Phospholipids
• Galactolipids
• lipoproteins

Substances obtained by hydrolysis of lipids
Natural fats
waxes
4
Simple lipidsNatural fats or (Triglycerides,
Triacylglycerols)

• They are esters of 3 fatty acids with the
  tri-hydroxy alcohol glycerol
• They include two types
• Solid at ordinary temperature FATs
• Liquid at ordinary temperature OILs
• Occurrence of neutral fat
• 1- in plants e.g. oils of cotton seed, olive,
  lin seed , palm oil, coconut .etc
• 2- in animals e.g. butter, lard etc
• 3- in marin oils e.g. oils of sea animals as
  cod liver

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Chemistry of Triacylglycerols

• Triacylglycerols are esters resulting from the
  reaction of
• fatty acids glycerol
• CH2- OH R1-COOH
  CH2-O-C-R1
• I
  -3 H2O I
• CH2 OH R2-COOH
  CH -O- C - R2
• I
  I
• CH2 OH R3-COOH
  CH-O- C- R3
• GLYCEROL 3 molecules of fatty acids
  Triacylglycerol

O
O
O
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Chemistry of Fatty Acids

• They are monocarboxylic acids (R- COOH) with
• 1- Hydrocarbon chain (R) hydrophobic
• 2- Carboxyl group (COOH ) that ionize to
  COO- (hydrophilic)
• so,
• Fatty acid is an amphipathic molecule
• i.e. it have both hydrophilic hydrophobic
  regions on the same molecule

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Classification of Fatty Acids in Nature
(according to saturation)

• 1- Saturated Fatty Acids
• contain even number of carbon atoms with no
  double bonds
• general formula Cn H2n1 COOH
• important examples
• Butyric acid (4C) CH3 - CH2 - CH2
  - COOH 40
• Palmitic acid (16 C) CH3 - (CH2)14
  COOH 160
• Stearic acid (18C) CH3 - (CH2)16 -
  COOH 180

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Classification of Fatty Acids according to
saturation (cont.)

• 2-
• 2- Unsaturated Fatty Acids
• They contain even number of carbon atoms
• and one or more double bonds
• The most important
• Oleic acid (18C) contains one double bond
  between C9 C10 in the chain
• 
  CH3-(CH2)7-CHCH-(CH2)7-COOH
• 
  181(9)
• Linoleic acid (18 C) contains two double
  bonds between C9 C10 and C12 C13
• 
  CH3-(CH2)4-CHCH-CH2-CHCH-(CH2)7-COOH
  
• 
  182(9,12)
• Linolenic acid (18 C) contains three double
  bonds between C9-10 , C12-13 C15-16
• 
  CH3-CH2-CHCH-CH2-CHCH-CH2-CHCH-(
  CH2)7-COOH

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Essential Fatty Acids

• Essential fatty acids
• can NOT be synthesized in human body.
• So, MUST be supplied with food.
• Two fatty acids are dietary essential in humans
• Linoleic acid
• precursor of arachidonic acid
• which is important for prostaglandin synthesis
• a-Linolenic acid
• precursor for other w3 (omega3) fatty acids
• which are important for growth and development

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Transport of Fatty Acids in Blood

• - Fatty acids are highly water-insoluble
• - So, a fatty acid must be transported in blood
  in with a protein
• 1- Fatty Acid Esters
• gt 90 of blood fatty acids are esters
• i.e. included in triacylglycerol, in
  cholesterol esters in phospholipids
• that are transported in blood with
  lipoprotein particles
• 2- Free Fatty Acids (Unesterified)
• lt 10 of blood fatty acids are free
  (unesterified)
• i.e. not bound to any other molecule
• They are transported in blood with albumin.

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Phospholipids

• PL are conjugated lipids
• PL are ionic polar structure formed of an
  alcohol that is attached by bridge to a back bone
  either diacylglycerol or sphinogosine

Long hydrophobic Tail
A
hydrophilic head
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Phospholipids Glycolipids
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Cholesterol
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Cholesterol (cont.)

• It is the major sterol in animal tissues
• It is available in cells of the body and in blood
• Most plasma cholesterol is in esterified form
  (bound with a fatty acid attached to C-3).
• Free cholesterol esterified cholesterol in
  blood is transported with a protein in
  liopoproteins
• Blood cholesterol level is normally 150-250 mg/dl
• High cholesterol levels in blood
  (HYPERCHOLESTEROLEMIA) may lead to
  ATHEROSCLEROSIS (i.e. deposition of cholesterol
  on inner walls of blood vessels)

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Cholesterol (cont.)

• Sources of cholesterol
• 1- Diet in animal sources
• 2- Synthesis by liver cells others
• Excretion of cholesterol
• cholesterol is excreted in bile
• BUT NOT excreted in urine

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Functions of Cholesterol

• 1- Cholesterol enters in the structure of cell
  membrane, brain, liver other
• organs
• 2- Cholesterol is the precursor for vitamin
  D3
• 3- Cholesterol is the precursor of steroid
  hormones
• 4- Cholesterol is the source of bile acids
  salts which are secreted with
• the bile juice essential for the
  digestion of lipids in the intestine

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Plasma Lipoproteins

• Plasma lipoproteins are spherical
  macromolecular complexes of
• lipids and proteins (apoproteins,
  apolipoproteins)
• They include
• chylomicrons,
• very low density lipoproteins (VLDL),
• low density lipoproteins (LDL)
• high density lipoproteins (HDL)
• They differ in lipid protein composition, in
  size, density site of origin
• lipoproteins function to keep their component
  lipids soluble to
• transport them in plasma

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Structure of Plasma Lipoproteins

• lipoproteins are composed of lipids
  proteins
• 1 - a neutral lipid core of hydrophobic
  lipid
• (containing triacylglycerol and
  cholesterol esters)
• 2 - surrounded by a shell of amphipathic
  lipids
• (phospholipids nonesterified
  cholesterol)
• 3 - Then, the outermost layer is amphipathic
  apolipoprotein (protein)
• Amphipathic compounds are oriented so that their
  polar portions are exposed on the surface of the
  lipoprotein thus making the particle soluble in
  aqueous solution
• The triacylglycerol and cholesterol carried by
  the lipoproteins are obtained either from the
  diet (exogenous source) or from de novo synthesis
  (endogenous source)

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Structure of Plasma Lipoproteins
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Size Density of Plasma Lipoprotein Particles

• 1- Chylomicrons
• lowest in density largest size of all
  lipoproteins
• contains the highest percentage of lipid the
  lowest percentage of protein
• 2- VLDLs LDLs
• are denser, having higher ratios of protein to
  lipid than chylomicrons
• 3- HDL
• the densest as it contains the highest level of
  protein to lipid in all lipoproteind
• Plasma lipoproteins can be separated
• - on the basis of their electrophoretic
  mobility (lipoprotein electrophoresis)

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Plasma Lipoprotein Electrophoresis
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Functions of plasma lipoproteins

• Chylomicrons
• They carry dietary lipids (TG
  Cholesterol) fat soluble vitamins to blood.
• Very low density lipoproteins (VLDL)
• is to carry lipid from the liver to
  tissues.
• Low density lipoproteins (LDL)
• transfers cholesterol from blood to
  tissues (originated from VLDL in blood).
• High density lipoproteins (HDL)
• HDL takes cholesterol from peripheral
  tissues and transfers it to liver.