Prof. Dr. Suat Erdoğan EBN School of Medicine Medical Biochemistry Department October 2013.
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Transcript of Prof. Dr. Suat Erdoğan EBN School of Medicine Medical Biochemistry Department October 2013.
Prof. Dr. Suat ErdoğanEBN School of Medicine
Medical Biochemistry DepartmentOctober 2013
OutlineDescription of lipidsFunction of lipids Fatty acids Triglycerides Cholesterol Steroids
LipidsLipids (or fats) are 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 nonpolar solvents, including ether, chloroform, benzene and acetone.
Major lipids Lipids may be polar or nonpolar
(amphipatic). Polar lipids have limited solubility in water because they are amphipatic.
Major lipids includetriacylglycerols, phosphodiacylglycerols,
sphingolipids, glycolipids, lipid-soluble vitamins, and prostaglandins
cholesterol, steroid hormones, and bile acids
Properties of LipidsDo not readily dissolve in waterFats are solid at room temperatureOils are liquid at room temperatureTriglycerides are the main form of
lipids in food and body (storage)Energy dense (9 kcal/g)
Functions of LipidsProvide energy Efficient storage of energyInsulationProtectionTransport fat-soluble vitaminsMembrane componentsSatietyFlavor and mouth feel
Provide and Provide and storage of energy storage of energy
In the body, fat serves as an efficient source of energy (ATP), both directly and potentially when stored in adipose tissue.
Fat cells in the bodyThe fat is stored in living cells, called fat cells (= adipocyte). Adipocytes makes adipose tissue.
Isolation Fats serves as a thermal
insulator in the subcutaneous tissues and around certain organs, and
Nonpolar lipids act as electrical insulators allowing rapid propagation of depolarization waves along myelinated nerves.
Protection Protection Below the dermis lies a layer of fat that helps insulate the body from heat and cold, provides protective padding, and serves as an energy storage area.
Transport fat-soluble vitaminsCombinations of fat and protein (lipoproteins) are important cellular constituents, occurring both in the cell membrane and in the mitochondria within the cytoplasm, and serving also as the means of transporting lipids in the blood.
Membrane componentsMembrane componentsMembrane lipids are a group of compounds (structurally similar to fats and oils) which form the double-layered surface of all cells. The three major classes of membrane lipids are phospholipids, glycolipids, and cholesterol.
SatietySatietyLipids suppress food intake when present in the small intestine of both humans and animals.
Flavor and mouth feelFlavor and mouth feelFats have little taste, but contribute
mouth feel and carry odorants.
Fat has a major influence on the sensory perception of food products. Fats enhance the taste and acceptability of foods, and lipid components largely determine the texture, flavor and aroma of foods.
LipidsLipids are classified as simple and complex are classified as simple and complex
1. Simple lipids: esters of fatty acids with various alcohols.a.Fats: esters of fatty acids with glycerol. A fat in the liquid state is known as oil.b.Waxes
2. Complex lipids: esters of fatty acids containing groups in addition to an alcohol and fatty acids.PhospholipidsGlycolipidsOther complex lipids
Fatty acidsFatty acids occur mainly as esters in natural fats
and oils but do occur in the unesterified form as free fatty acids (FFA), a transport form found in the plasma.
The fatty acid chain may be saturated (containing no double bonds) or unsaturated (containing one or more double bonds). Unsaturated fatty acids may be further subdivided as follows:
a.Monoansaturated acids, containing one double bond (oleic acid).
b.Polyunsaturated acids containing two or more double bonds (linoleic acid, arachidonic acid).
omega end alpha end
degree of saturation
H H H H H H H H H H H H H H H H H O
H-C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C-C-OH
H H H H H H H H H H H H H H H H H
Stearic acid: C18H38O2
Saturated fatty acidsLauric acid (12 C) Myristic acid (14 C) Palmitic acid (16 C) Stearic acid (18 C) Arachidic acid (20 C)
Unsaturated fatty acids Palmitoleic acid (16:1) Oleic acid (18:1) Linoleic acid (18:2) -Linolenic acid (18:3) -Linolenic acid (18:3) Arachidonic acid
(20:4)
16:1 mean: a fatty acid contains 16C and 1 double bond in the structureColored in red demonstrates essential fatty acids.
Deficiency of essential fatty acidsDeficiency of essential fatty acidsEssential fatty acid
deficiency results in dermatitis.
Clinical signs of essential fatty acid deficiency include a dry scaly rash, decreased growth in infants and children, increased susceptibility to infection and poor wound healing.
omega end alpha end
One double bond
H H H H H H H H H H H H H H H O
H-C--C--C--C--C--C--C--C--C=C--C--C--C--C--C--C--C--C-OH
H H H H H H H H H H H H H H H H H
omega end alpha end
> 2 double bonds
H H H H H H H H H H H H H O
H-C--C--C--C--C--C=C--C--C=C--C--C--C--C--C--C--C--C-OH
H H H H H H H H H H H H H H H H H
omega end alpha end
1st double bond is located on the 6th carbon from the omega end
H H H H H H H H H H H H H O
H-C--C--C--C-- C--C =C--C--C=C--C--C--C--C--C--C--C--C-OH
H H H H H H H H H H H H H H H H H
Omega-6 (linoleic) fatty acidFound in vegetable oilsOnly need ~ 1 tablespoon a dayArachidonic acid can be made from
omega-6Metabolized to form eicosanoids
omega end alpha end
1st double bond is located on the 3rd carbon from the omega end
H H H H H H H H H H H H H H H H H O
H-C--C--C=C--C--C =C--C--C=C--C--C--C--C--C--C--C--C-OH
H H H H H H H H H H H
Omega-3 (linolenic) fatty acidPrimarily from fish oilAlso found in canola or soybean oilMetabolized to form eicosanoidsRecommend intake of ~2 servings of fish
per week.
Essential Fatty AcidsMust be eatenBody can only make double bonds
after the 9th carbon from the omega end.
Needed for immune function, vision, cell membrane, and production of hormone-like compounds.
Signs and Symptoms of Essential Fatty Acids Deficiency
Itchy skinDiarrheaInfectionsRetarded growth and wound
healingAnemia
Fats
Triglycerides (=triacylglycerol)Triglycerides are the main storage forms of fatty
acids. Triglycerides are esters of the alcohol glycerol
and fatty acids.
(Ester bond)
Glycerol + 3 FA’s Triglyceride + 3 H20
H
H--C--OH
H--C--OH
H--C--OH
H
O
HO-C-R
O
HO-C-R
O
HO-C-R
+
H O
H--C--O--C--
O
H--C--O--C--
O
H--C--O--C--
H
R + H2O
R + H20
R + H20
esterification/reesterification
desterfication
H
H--C--OH
H--C--OH
H--C--OH
H
Fatty Acid
Fatty Acid
Fatty Acid
+
H O
H--C--O--C--
O
H--C--O--C--
O
H--C--O--C--
H
Fatty Acid
Fatty Acid
Fatty Acid
Trans and cis fatty acids
PhospholipidsPhospholipids are a class of lipids that are a
major component of all cell membranes as they can form lipid bilayers. Phospholipids contain a diglyceride, a phosphate group and choline.
Built on a glycerol backboneHas at least one fatty acid replaced with
phosphorus containing compoundFound in bodySynthesized by the body as needed
Structure of phospholipids
Functions of PhospholipidsMakes up cell membraneEicosanoid synthesisEmulsifier
Bile acidsLecithins
Hydrophilic end
(attracts water)
Hydrophobic end (attracts lipid)
Emulsification Emulsification refers to the process of dispersing a substance such as oil in an emulsion. It also refers to the process of converting two or more immiscible liquids into an emulsion. During this process, large fat globules are broken down into smaller, evenly distributed particles.
GlycolipidsGlycolipids are lipids with a carbohydrate attached to an -OH of the lipid. Their role is to provide energy and also serve as markers for cellular recognition.
O
(CH2)12CH3
HO
NHCRO
O
H
HO
H
HO
H
HOH
H
OH
a-glucosidebond
a unit of -D-glucopyranose
SterolsSterols, also known as steroid alcohols, are a subgroup of the steroids and an important class of organic molecules. They occur naturally in plants and animals, with the most familiar type of animal sterol being cholesterol. Cholesterol is vital to animal cell membrane structure and function and a precursor to fat-soluble vitamins and steroid hormones.A multi-ringed structureDo not have a glycerol backboneDo not readily dissolve in water
Functions of CholesterolEssential component of
cell membraneProduced by the liverFound only in animal
productsForms important
hormonesEstrogen, testosterone,
vitamin DPrecursor to bile acids
AndrogensAndrogens - male sex hormones
synthesized in the testesresponsible for the development of male
secondary sex characteristics
AndrosteroneTestosteroneO
HOH
H
H3C H
H
H3C H3C
H
HH3C
H
O
HO
EstrogensEstrogens - female sex hormones
synthesized in the ovariesresponsible for the development of female
secondary sex characteristics and control of the menstrual cycle
Progesterone Estradiol
H3C
H
HH3C
H
C=OH
O
CH3OH
HO
H
H
H
H3C
EicosanoidsA group of hormone-like compounds
Regulates blood pressure, childbirth, clotting, immune responses, inflammatory responses, & stomach secretions
By-pass the blood stream and work in the area of origin
Eicosanoids Have Different EffectsOmega-6 eicosanoids; archidonic acid
increase blood clottingincrease inflammatory responses
Omega-3 eicosanoids decrease blood clottingreduce heart attackexcess may cause hemorrhagic stroke
Eicosanoid has different effect on different tissues.
ProstaglandinsProstanoids are a subclass of eicosanoids consisting of the prostaglandins (mediators of inflammatory and anaphylactic reactions), the thromboxanes (mediators of vasoconstriction), and the prostacyclins (active in the resolution phase of inflammation.)
Prostanoic acid
192018
1716
1514
13
78
9
10
1112
65
43
21CO2H
ProstaglandinsProstaglandins are not stored in tissues as
such, but are synthesized from membrane-bound 20-carbon polyunsaturated fatty acids (arachidonic acid) in response to specific physiological triggers
Arachidonic acid1514
89
11 12
6 5CO2H
ProstaglandinsResearch on the involvement of PGs in
reproductive physiology has produced several clinically useful derivatives15-Methyl-PGF2 is used as a therapeutic
abortifacient
15
15-Methyl-PGF2
extra methyl groupat carbon-15
CO2H
HO
HOHO CH3
LeukotrienesLeukotrienes: derived from arachidonic acid
found in white blood cells (leukocytes)an important property is constriction of smooth
muscles, especially in the lungs
L-cysteine
Leukotriene C(its synthesis and release is
triggered by allergic reactions)
NH2
H S
HO H
CO2H
CH2CH2CHCO2-
Thromboxanesderived from arachidonic acidcontain a four-membered cyclic ether within a
six-membered ringinduce platelet aggregation and smooth muscle
contraction
(a potent vasoconstrictor)Thromboxane A2
CO2HO
OH
O
H
H
What are lipoproteins?A lipoprotein is a biochemical assembly that contains both proteins and lipids. The lipids or their derivatives may be covalently or non-covalently bound to the proteins. Examples include the high density (HDL) and low density (LDL) lipoproteins which enable fats to be carried in the blood stream, the transmembrane proteins of the mitochondrion and the chloroplast, and bacterial lipoproteins function of lipoprotein particles is to transport water-insoluble lipids (fats) and cholesterol around the body in the blood.
Classification of Lipoproteins
Atherosclerosis
Summary A knowledge of lipid biochemistry is important in understanding many current biomedical areas of interest e.g. obesity, diabetes, atherosclerosis, and the role of various polyunsaturated fatty acids in nutrition and health.
Content ReviewWhat are some important functions
of the essential fatty acids?How are saturated fatty acids
different from unsaturated fatty acids?
What is esterification?What are the main functions of lipid
in the body?What are emulsifiers?
