Transcript essential fatty acid

CHAPTER THREE: BIOCHEMISTRY
CARBOHYDRATES
There are three main types of carbohydrates:
• monosaccharides – these are simple sugars which cannot be broken down to
anything simpler.
• disaccharides – double sugars, yield two monosaccharides on hydrolysis.
• polysaccharides – complex sugars, yield many simple sugars on hydrolysis.
MONOSACCHARIDES
Categorized according to the number of carbons.
Hexoses - glucose, fructose and galactose.
All contain 6 carbon atoms.
CHO
H
HO
OH
H
H
OH
H
OH
CH2OH
H OH
H O
HO
HO
H
H
H
OH
OH
glucose
Chapter 3/p1
NB. For properties of glucose, fructose and galactose, refer to notes.
IDENTIFICATION OF GLUCOSE
To test for glucose in the urine which is a strong indication of diabetes, add
Benedict’s reagent.
Glucose (-CHO) + Cu2+ + OH- → - COO- + Cu2O
blue solution
red ppt.
DISACCHARIDES
Sucrose, maltose and lactose.
Sucrose – glucose + fructose, found in sugar cane and sugar beet.
Maltose – glucose + glucose, malt sugar – hydrolysis of starch.
Lactose – glucose + galactose, milk sugar.
POLYSACCHARIDES
Starch, cellulose, glycogen and dextrin.
Chapter 3/p2
LIPIDS
Lipids are organic compounds and in general:
• insoluble in water.
• soluble in nonpolar organic solvents such as ether, acetone and carbon
tetrachloride.
• contains carbon, hydrogen and oxygen; sometimes contain nitrogen and
phosphorus.
• yield fatty acids on hydrolysis or combine with fatty acids to form esters.
• Take part in plant and animal metabolism.
FATTY ACIDS
Straight – chain organic acids and contain an even number of carbon
atoms.
Can be either saturated or unsaturated.
Saturated fatty acids contain only single bonds between carbon atoms
whereas unsaturated fatty acids contain a few double bonds between carbon
atoms.
Polyunsaturated fatty acids contain many double bonds.
Chapter 3/p3
Unsaturated fatty acids can be subdivided into the following categories:
• monounsaturated, only one double bond.
• polyunsaturated – many double bonds.
• eicosanoids – includes prostaglandins, leukotrienes, prostacyclins and
thromboxanes.
Linoleic acid is called the nutritionally essential fatty acid – it is essential for
the complete nutrition of the body.
The absence of the essential fatty acid from the diet of an infant causes loss of
weight.
CLASSIFICATION OF LIPIDS
SIMPLE LIPIDS
Simple lipids are esters of fatty acids.
Hydrolysis of a simple lipid may be expressed as:
simple lipid + H2O
hydrolysis
fatty acid(s) + alcohol
Chapter 3/p4
If the hydrolysis of a simple lipid gives three fatty acids and glycerol, the
simple lipid is called a fat or an oil.
If the hydrolysis of a simple lipid gives a fatty acid and a high molecular mass
monohydric alcohol, the simple lipid is called a wax.
COMPLEX LIPIDS
Complex lipids on hydrolysis yield one or more fatty acids, an alcohol and
some other type of compound.
Some examples are phospholipids and glycolipids.
Phospholipids undergo hydrolysis as follows:
phospholipid + H2O
hydrolysis
fatty acid(s) + alcohol + phosphoric acid + a
nitrogen compound
Chapter 3/p5
FATS AND OILS
Fats are esters formed by the combination of a fatty acid with glycerol.
Unsaturated fats and oils combine with iodine whereas saturated fats and
oils will not.
The iodine number of a fat or oil is the number of grams of iodine that
will react with the double bonds present in 100 g of that fat or oil.
The higher the iodine number, the greater the degree of unsaturation of
the fat or oil.
In general, animal fats have a lower iodine number than vegetable oils.
SOAPS
Soaps are produced by the saponification of fats, soaps are salts of
fatty acids
C17H35COOH
stearic acid
+
NaOH
sodium hydroxide
→
C17H35COONa
+ H2O
sodium stearate, a soap
Chapter 3/p6
WAXES
Compound produced by the reaction of a fatty acid with a high molecular
mass monohydric alcohol such as ceryl alcohol, C23H53OH.
STEROIDS
e.g. cholesterol.
Chapter 3/p2
PROTEINS
AMINO ACIDS
Building blocks of proteins.
An amino acid is an organic acid that has an amine (-NH2) group attached
to a chain containing an acid group.
Amphoteric compounds, i.e. can react with an acid or base, account for
their ability to act as buffers in the blood.
At a certain pH, amino acids will not migrate towards the positive or the
negative electrode, they will be neutral, i.e. there will be an equal number of
positive and negative ions.
This point is called the isoelectric point.
DIPEPTIDES
Proteins consist of many amino acids joined together by what is called a
peptide linkage or a peptide bond.
Chapter 3/p8