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Carbohydrates .
Proteins .
Lipids .
Nucleic Acids .

• Carbohydrates are the most abundant biomolecule on earth .
Chemically carbohydrates are polyhydroxy ketone or aldehyde derivatives , or substances that yeild such compounds on hyderolysis. Many have the emperical formula (CH
2
O) n
Where n is 3 or larger .
• Biological significance of carbohydrates;
Carbohydrate functions as an energy source for cells (acts as
Bio fuel), producing 4kcal/g of carbohydrate.

 They act as forms of energy storage (carbohydrates are stored in the form of glycogen in animal cells, while stored as starch in plant cells)
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They have a structural role (Cellulose forms cell wall of plant , Peptidoglycan forms cell wall of bacteria).
They have other specialized functions such as an
anticoagulant, Heparin is a polysaccharide
(carbohydrate) which acts as anticoagulant and prevents intravascular clotting.
Carbohydrate functions as Antigen,
Many antigens are glycoprotein (which contains oligosaccharide) in nature and give immunological properties to the blood.

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– Monosaccharide .
– Disaccharide .
– Oligosaccharides .
– Polysaccharide .

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Are the simplest form of carbohydrates consisting of a single polyhydroxy aldehyde or ketone unit .
They resemble the building block of carbohydrates .
The monosaccharide can be a ketone or aldehyde sugar.
All monosaccharides have reducing powers.
The most abundant monosaccharide in nature is glucose.
Examples of monosaccharides;

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Disaccharides; They consist of two monosaccharides joined covalently by a glycosidic bond.
Some have reducing powers (those that have a free carbonyl group) some lack reducing powers (those that lack a free carbonyl group).
Example of a non-reducing disaccharide , sucrose ;
 Reducing disaccharide
Maltose .

How do two monosaccharides combine to make a disaccharide ?
- By dehydration reaction and formation of O-Glucosidic bond .

 Oligosaccharides; oligosaccharides consist of short chains of monosaccharide units or residues (3-10 ) joined by glycosidic bonds.
 Polysaccharides;
The most abundant carbohydrates in nature are polysaccharides.
-They are made up of a large number of monosaccharide units (hundreds or thousands) joined by glycosidic bonds.
- They can form linear(amylose) , or branched chains
(amylopectin).

 They can be made up of repeating units of a single type of monosaccharide (homopolysaccharides) , or made up of two or more different types of monosaccharides
(heteropolysaccharides).

Polysaccharides are long chains of monosaccharides linked together .

 Lipids represent a group of heterogenous compounds
,chemically they are a diverse group of compounds that are united by their common defining feature which is their insolubility in water and solubility in organic solvents ( such as ether , benzene).
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Biological significance of lipids ;
Concentrated source of energy (9 kcal/gm)
Energy reserve: any excess energy from carbohydrates, proteins and lipids are stored as triglycerides in adipose tissues

Provide insulation to the body from cold
 Maintain body temperature
 Mechanical insulation
 Protects vital organs.
 Electrical insulation
 Protects nerves, help conduct electro-chemical impulses (myelin sheath).
 Supply essential fatty acids (EFA)
 They have a structural role;
 Phospholipids, are a major component of cell membranes.

Examples of lipids;
1- Fatty acids ;
They are carboxylic acids with hydrocarbon chains ranging from 4-36 carbons long.
 With a few exceptions, natural fatty acids:
 Contain an even number of carbon atoms
 Arranged in an unbranched line
 Have a carboxyl hydrophylic group (-COOH) at one end.
 Have a long hydrophobic hydrcarbon chain that ends with a methyl group (CH
3
) at the other end.

Fatty acids could be saturated (contain single C-C bonds
))
Or unsaturated (contain double C= C bonds ) .

fatty acids are amphipathic molecules that have a polar hydrophylic head( Coo-) and a non-polar hydrophobic hydrocarbon chain .

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2- Triacylglycerols;
They are the most abundant fat in food .
Fat is stored in our bodies in the form of triacylglycerols
(triglycerides)
Triacylglycerols are composed of a glycerol unit linked by ester bonds to three fatty acids .

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There are two types of nucleic acids , DNA
(deoxyribonucleic acid) and RNA (ribonucleic acid).
The function of the DNA molecule is to preserve and carry the genetic information needed for the development and functioning living organisms .
RNA molecules play an important role in the biosynthesis of proteins.
 DNA is a normally a double stranded macromolecule , made up of two polynucleotide chains twisted and held together by a large number of hydrogen bonds , forming the double helix structure.
- Neocleotides are the building blocks of both DNA and
RNA molecules.

 A molecule of DNA is made up of millions of nucleotides.
 Each nucleotide consists of:
1.
2.
3.
Phosphate group
Pentose sugar
Nitrogenous base
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Phosphate
Nitrogenous
Base
Pentose
Sugar

 The pentose sugar is 2-deoxyribose in the case of DNA , and ribose in RNA.

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Nitrogeneous bases ;
In DNA ; Adanine , Guanine , Cytosine and thymine.
 In RNA ; Adanine , Guanine , Cytosine and
Uracil.

Neocleotides are linked together in the polyneocleotide chain through a 3 5 phosphodiester bond.

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Is made up of a single strand of polyneocleotides.
There are three types of RNA molecules ; mRNA ( messenger RNA) ; it carries the genetic information from the DNA in the nucleus to the ribosomes for protein synthesis.
tRNA(transfer RNA) , carries the amino acids from the amino acid pool to the ribosomes during protein biosynthesis.
rRNA(ribosomal RNA) is part of the ribosome structure and is involved in translating the genetic code carried by the mRNA during protein biosynthesis.

Proteins are the most diverse biomolecule and is virtually involved in every activity in the living cell .
-Proteins are polymers of amino acids , they are made up of a large number of amino acids joined together by peptide bonds .
The peptide bond formation involves a dehydration reaction.
The number and sequence of amino acids in a protein is genetically determined.
- Proteins occur in great variety; thousands of different kinds, ranging in size from relatively small peptides to huge polymers with molecular weights in the million
The building blocks of proteins are amino acids.

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Functions of proteins ;
-Catalytic functions, (enzymes).
- Cellular Receptors (insulin receptor).
- Structural function (collagen), proteins are a major component in cell membranes.
-Transport (haemoglobin, albumin).
Protective functions antibodies(immunoglobulins i.e
antibodies ).
- Blood clotting factors (fibrinogen)
- Hormonal functions [insulin, glucagon, GH]
- DNA packing [histones]
- Act as buffers.

■ The 20 amino acids commonly found as residues in proteins contain an αcarboxyl group, an αamino group, and a distinctive R group substituted on the α-carbon atom.
General structure of an amino acid