Biochemistry of Lipids PDF

Biochemistry of Lipids Dr. Margaret Doherty Lipids Lipids Atlantic Technological University Definition Function Classes Nomenclature Simple and Complex  Definition of lipids...

Biochemistry of Lipids Dr. Margaret Doherty Lipids Lipids Atlantic Technological University Definition Function Classes Nomenclature Simple and Complex  Definition of lipids Atlantic Technological University Lipids are defined as water insoluble organic biomolecules - composed of C, H, O (some contain P) - can be extracted from cells and tissues by non-polar solvents e.g. chloroform, benzene or ether  Function of lipids Atlantic Technological University Structural Precursor of Act as Protection of Storage form component many steroid thermal internal of energy of cell hormones, insulator organs membrane. vitamin D  Function of lipids Atlantic Technological University Fats serve as Helps in Acts as Lipoproteins surfactants Improve absorption electric transporting by reducing taste and of fat soluble insulators in lipids surface palatability. vitamins neurons. tension.  Classification of Lipids Simple Lipids Complex Lipids Atlantic Technological University Fatty Acids Phospholipids Steroids Glycolipids (Cholesterol) Triglycerols Sphingolipids  Fatty Acids (FAs) These are building blocks for complex lipids Atlantic Technological University e.g. Triglycerides contain three fatty acids and a glycerol Provide a lot of energy Precursors of other important compounds e.g. Certain hormones May have a major impact on health - Risk of Cardiovascular Disease  Types of Fatty Acids The Length of Carbon Chain Atlantic Technological University Long chain Medium chain Short chain Degree of Saturation Saturated Unsaturated Location of Double Bonds Omega 3 fatty acids Omega 6 fatty acids  Atlantic Technological University Length of Carbon Chain  Saturated Atlantic Technological University Degree of Unsaturation Monounsaturated Unsaturated Cis/Trans Polyunsaturated  Saturated Fatty Acid All Single Bonds between Carbons Atlantic Technological University Monounsaturated Fatty Acid One carbon-carbon double bond Atlantic Technological University Polyunsaturated Fatty Acid Two or more carbon-carbon double bonds Atlantic Technological University Atlantic Technological University  Fatty Acids (FAs) Saturated chains pack Atlantic Technological University tightly and form more rigid, organized aggregates (i.e., membranes) Unsaturated chains bend and pack in a less ordered way, with greater potential for motion  Structure of FAs All contain Atlantic Technological University - A long hydrocarbon chain - Terminal carboxyl group The chain length varies 4 carbons – 22 carbons The nature of the chain varies - Saturated or unsaturated i.e. no double bonds vs. double bonds The number/position of double bond can vary  Essential fatty acids Most saturated and monounsaturated fatty acids can be Atlantic Technological University synthesized by mammals Unable to synthesis linoleic (Ω6) and linolenic acid (Ω3) - Essential fatty acids - Necessary in diet - If absent in the diet, deficiency diseases arise  Fatty acid Nomenclature Atlantic Technological University Nomenclature reflects the location of the double bond The Δ system counts from the carboxyl end Find Carbon in the carboxyl group - # No. 1 Subsequent carbons numbered sequentially 2,3,4,5 etc.  Atlantic Technological University Carboxyl Group Butanoic acid  Atlantic Technological University Carboxyl Group 1 Butanoic acid 2 3 4  Shorthand notation A shorthand notation is used indicating Atlantic Technological University The number of carbons in the chain The number double bond(s) in the hydrocarbon chain, if any The position of any double bonds in the hydrocarbon chain, counting from the carboxyl carbon (i.e. carbon #1) Double bond in carboxyl group not included Double bonds assumed to be cis-type (natural fats)  Butanoic acid Atlantic Technological University 4 3 2 1 Shorthand notation: C4:0  Linoleic acid Atlantic Technological University Shorthand notation: C18:29,12  ω – notation system The number of carbons in the chain Atlantic Technological University The number double bond(s) in the hydrocarbon chain The position of the double bonds in the hydrocarbon chain numbering from the methyl group (CH3-) which is done by using the symbol ω e.g., linoleic acid is represented by 18:2 ω6  Linoleic acid Atlantic Technological University Omega notation count this way! 18:2 ω6  Omega (ω) – notation system Ω-3 (omega 3) fatty acids are Atlantic Technological University - polyunsaturated fatty acids - Have the first double bond at carbon #3 starting from the methyl carbon Ω-3 fatty acids are thought to have major health benefits Ω-6 fatty acids are - polyunsaturated fatty acids - have the first double bond at carbon #6 - starting from the methyl carbon  Lipolysis Hydrolysis of lipids by Atlantic Technological University lipase Occurs in fat adipocytes Glycerol and free fatty acids are released  Steroids Many different compounds Atlantic Technological University Distinctive functions / activities All originate from a terpene called squalene Cholesterol - Most abundant steroid in animal tissues Precursor of bile acids, androgens (male hormones), oestrogens (female hormones) and other hormones Excessive blood cholesterol is associated with increased risk of atherosclerosis  Cholesterol The liver is primary site of cholesterol synthesis Also be acquired from diet Atlantic Technological University Intake of dietary cholesterol reduces the synthesis of cholesterol Adults on a low cholesterol diet - synthesize c.800 mg cholesterol / day Two different classes of lipoprotein carry cholesterol around the body - LDLs - HDLs  Low-density Lipoprotein Atlantic Technological University Contain largest portion of total cholesterol Carry cholesterol to the tissues High levels of LDLs associated with increased risk of cardiovascular disease (CVD)/heart attack Diets high in monounsaturated fat/ low in saturated fats decrease the LDL cholesterol which, in turn, results in a reduction in the risk of CVD  High-density Lipoprotein Transport cholesterol from the tissues to the liver Atlantic Technological University High levels of HDLs are associated with decreased risk of CHD Diets high in polyunsaturated fats beneficially decrease LDL cholesterol  Triacylglycerols (Triglycerides) Atlantic Technological University Most abundant family of lipids Major component of deposit or storage lipids in plant and animal cells In animal, the deposit lipids are stored as adipose tissue 98-99% of vegetable oil and the lipid component of butter, lard  Structure of Triglycerides Atlantic Technological University Glycerol backbone Three fatty acid residues are bound all three -OH groups of glycerol are esterified with fatty acids Most animal fats and plant oils are extremely complex mixtures of triglycerides  Atlantic Technological University A Triglyceride  Properties of Triglycerides Melting point increases as the number of carbons Atlantic Technological University increases and as the number of double bonds decreases Solubility Unsaturated are usually liquid at room temperature Saturated are usually solid at room temperature Lipolysis (as described for FA) Autoxidation  Phospholipids Atlantic Technological University Includes Phosphoglycerides Complex lipids Major components of cell membranes  Phospholipid Structure Atlantic Technological University Phospholipids consist of a backbone of glycerol There are two fatty acids esterified to the glycerol molecule The phosphoric acid residue to which the alcohol is esterified varies The nature of the alcohol varies Depends on the phospholipid e.g. Choline, Ethanolamine  Atlantic Technological University Phosphatidyl ethanolamine  Atlantic Technological University Amphipathic molecule  Occurrence Very important components of cell membranes The most abundant phosphoglycerides in higher plants and Atlantic Technological University animals are: 1. Phosphatidylethanolamine (cephalin) This important phospholipid contains ethanolamine as the alcohol group 2. phosphatidyl choline (lecithin) This phospholipid contains choline as the alcohol group Other phospholipids include: - phosphatidyl serine - phosphatidyl glycerol  Glycolipid Atlantic Technological University Contain both carbohydrate and lipid components. Derivatives of ceramide Key component of cell membrane – stability, cell-cell interaction Act as Cell surface receptors  Sphingolipids Atlantic Technological University Important membrane components in both plants and animals Present in especially large amounts in brain and nerve tissue Only trace amounts are present in fat deposits Contain sphingosine as backbone  Sphingolipids All sphingolipids contain three characteristic building block Atlantic Technological University components: 1) A molecule of fatty acid, 2) A molecule of sphingosine, 3) A polar head group e.g. phosphoethanolamine, phosphoryl choline