Lipids

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					   Def: lipids are heterogeneous group related
    to fatty acids.
   Lipids are relatively insoluble in water.
   They are soluble in nonpolar solvents such as
    chloroform , diethyl ether, acetone, benzene
    and ether.
   The hydrophobic (water hating) nature of
    lipids is due to the predominance of
    hydrocarbon chain.(-CH2-CH2-CH2-) in their
    structure
   Lipids are important dietary constituent
    because:
   A) They are a source of high energy value.
   B) They contain fat soluble vitamins.
   C) They contain essential fatty acids.
   Lipids in adipose tissues serve as storage
    form of energy.
   They serve as thermal insulator in the
    subcutaneous tissues.
   Lipoproteins(a combination of fat and
    proteins) are important because:
   1. They enter in the structure of cell
    membrane and mitochondria.
   2. They serve as a transport form of lipids in
    the blood .
   Simple
   Complex
   Derived
   Simple lipids are esters of fatty acids with
    various alcohols.
   (Ester bond = R-coo-R).They are either fat or
    waxes.
   R-COOH(H) + R-(OH)=> R-COOH-R + H2O
   Are esters of fatty acids with glycerol .Fat are
    either solid or liquid.
   Are esters of fatty acids with higher molecular
    weight alcohols containing one (-OH) group
    i.e monohydric alcohols.
   Are esters of fatty acids and alcohols ,in
    addition of other groups . They include:
   Phospholipids: they consist of
   Fatty acids + alcohols + phosphoric acids
    residue + nitrogenous base. They include:
   Glycerophospholipids : when alcohol is
    glycerol.
   Sphignophospholipids : where the alcohol is
    sphingosine.
   Glycolipids : they consist of fatty acids +
    sphingosine + carbohydrate.
   Other complex lipids are :which include
    sulpholipids (containg suphur) ,amino
    lipids(containing amino acids) and
    lipoproteins (containing proteins).
   Substance which are given by hydrolysis of
    simple and complex lipids.
   Substance which are insoluble in water but
    soluble in nonpolar solvents as :
   Fatty acids.
   Glycerol
   Steroids
   Alcohols
   Ketone bodies
   Fatty aldehydes
   Neutral lipids: are those which carry no
    charge and include:
   Neutral fats: (acylglycerols).
   Cholesterol and cholesteryl esters.
   Water insoluble
   They are monocarboxylic
   They are mostly aliphatic (not branched)
   Fatty acids are present as free fatty acids in
    plasma.
   Fatty acids occur in natural fats contain an even
    number of carbon atoms , because they are
    synthesized from 2 carbon units.
   Fatty acids may be saturated (containing no
    double bonds) or unsaturated (containing one or
    more double bonds).
   Solubility:
   Short chain fatty acids e.g acetic (2C) and butyric
    (4C) are soluble in water.
   Long chain fatty acids are insoluble in water in
    nonploar solvents.
   Melting points: this depend upon length on fatty
    acids and the degree of unsaturation , so
   1.short chain and unsaturated fatty acids are
    liquid at RT.
   2.long chain and saturated fatty acids are solid at
    RT
   Have no double bonds in the chain’.
   General formula is -CH3-(CH2)n-CooH
    ,where (n) equals the number of methylene (-
    CH2) group between the methyl and
    carboxylic group.
   The systemic name of saturated fatty acids
    ends by the suffix (-anoic).e.g palmitic
    acids(16 C) has symmetric name hexadeconic
    acids(hexa =6;deca10)
   Have one (monosaturated) or more
    (polyunsaturated) double bonds in the chain.
   The general formulae is Cn-H2n-1-COOH.
   The systemic name is unsaturated fatty acids
    ends by the suffix (-enoic) e.g oleic
    acids(18C) has systemic name octadecenoic
    acids (octa=8,deca=10)
   They are called non-essential fatty acids
    because they are synthesized in the body
    .Thus need not be obtained from the diet.
   They can be synthesized from acetyl CoA
    (Activate acetate) derived from glucose
    oxidation.
   They are called essential because they cannot
    be synthesized in the body . They must be
    supplied diet
   Essential fatty acids include those which
    contain more than one double bonds
    (polysaturated fatty acids) e.g linolenic acids
    and arachidonic acids.This is because there
    are no human enzyme that can be introduced
    a double bond except at the ninth carbon
    atoms(9-10) position.
   Normal growth
   They enter in the structure of phospholipids
    and cholesterol esters
   Vegetable oil e.g corn oil is rich in essential
    fatty acids
   They are formed only from alcohols and fatty
    acids.
   They are called neutral fats because they
    carry no charge.
   The main site for storage of fat in human is
    the cytoplasm of cells located in
    subcutaneous fat and around important
    organs . Adipose tissues is important source
    of energy .Each gram fat gives 9.3Kcal.
   Human fat is liquid at RT and contain high
    content of oleic acid.
   In animals      Butter and lards

   In plants       Cotton seed oil ,
                     linseed oil, sesame
                     oil and olive oil.

   Marine oil      Cod liver and shark
                     oil.
   These include phospholipids , glycolipids ,
    lipoproteins , sulpholipids , and aminolipids .
   Phospholipids :They contain phosphoric acids
    residues .They are classified into
    glycerophospholipids (contain glycerol) and
    sphingophospholipids(contain sphingosine).
   Structure :
   1. Glycerol
   2. Saturated fatty acid(attached to 1(α)
    position.
   3.Unsaturated fatty acids (attached to2(β)
    position.
   4. Choline base (attached to phosphoric acid.)
    .Base differs in various phopholipids.
   It enters in the structure of cell membrane .It
    is most abundant phopsholipid in cell
    membrane.
   It act as body store of choline.
    Importance of Choline :
   1. It is important in nerve transmitter.
   2. It acts as methyl donor in transmethylation
    reaction.
   3.Dipalmitoyl lecithine(i.e lecithine which
    contain 2 palmitic acid residue)acts as
    surfactant in the lung.
   Dipalmitoyl lecithine continuosly secreted by the
    lungs cells in the alveolar wall,forming a monolayer
    over the watery surface of the alveolus and so lower
    the surface tension .This help expiration and
    inspiration.
   During expiration ,the surfactant becomes solid
    under pressure . This prevents the adherence of
    alveolar wall.
   During inspiration ,the surfactant makes the lungs
    easier to expand.
   In premature babies :lungs do not secret enough
    surfactant .This leads to lungs collapse and death
    from respiratory failure . Treatment of this case need
    the putting babies in incubator and administration of
    surfactant locally in the lungs.
   It is one of activating factor of coagulation
    mechanism
   They are called complex glycolipids , because
    they contain in addition to hexose , one or
    more sialic acid molecules.
   Function:
   They acts as receptors at cell membrane
   They are present in high concentration in
    brain.
   Cholesterol(animal origin)
   Ergosterol (plant origin)
   Vitamin D group
   Bile salt
   Steroids hormones
   1.Male sex hormones
   2. Female sex hormones
   3.Adrenal cortical hormones
   Distribution in the body:
   It is present in all cells especially;
   Adrenal cortex.
   Liver and kidney
   Brain and nerve tissues
   The level of blood cholesterol is normally less
    than 220mg/dl . Any increase above this level
    is called as hypercholesterolemia.
   Structure: similar to cholesterol but differ in
   1.double bonds
   2. the side chain is unsaturated and has extra
    methyl group.
   Properties;
   It is plant sterol, poorly absorbed by small
    intestine.
   Function: It gives vitamin D2 by ultra violet
    rays.
   Bile salt are bile acids
   Function:Bile salts are important for digestion
    and absorption of lipids.
   Estrogens: 3 types ;estrone , estradiol and
    estriol.
   Site for production:
   1.Ovary and placenta in female
   2.Adrenal cortex in both male and female.
   Functions
   1.They stimulate the development of female
    sex characters and organs.
   Structure:
   Ketone group at C3
   Double bond between C4 and C5.
   Methyl group at C10 and C13
   Methylketone at C17
   Site of production:
   Ovary and placenta in female.
   Adrenal cortex in both male and female
   Function:
   It prepares the uterus for implantation of the
    ovum.
   It stabilizes pregenancy (prevent abortion)
   Testerone :
   Structure
   Ketone group at C3
   Double bond between C3 and C5.
   2 methly group at C10 and C13
   -OH at C17.
   Site of production:
   Intestinal cells of leyding of the testis in male
   Adrenal cortex in both male and female.
   Function: It stimulates the development of male
    sex characters and organs.
   Site of production:
   Adrenal cortex
   Function:
   Glucorticoids :control the metabolism of
    carbyhydrates , proteins, and fats.
   Minerlcorticoids: control the metabolism of
    Na ,KCl, and water.

				
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posted:10/12/2011
language:English
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