A polyhydroxy compound that has an aldehyde or a ketone functional group present, either free or as hemiacetal
or acetal are called carbohydrate.
Their structure has been elucidated as follows :
(i) Analysis and molecular-weight determinations show that the molecular formula of the aldohexoses is C6H12O6.
(ii) When treated with acetic anhydride, aldohexoses form the penta-acetate. This indicates the presence of five
Glucose : Glucose is the most common monosaccharide. It is known as Dextrose because it occurs in
nature principally as the optically active dextrorotatory isomers. It is act as a reducing agent (reduces both
Fehling’s solution and ammonical silver nitrate solution). When heated with sodium hydroxide, an aqueous
solution of glucose turns brown. It is known as dextrose and found as grapes, honey, cane sugar, starch and
cellulose
Chemical Reactions Reaction due to OH group
Structure
Either of 2 form (a & b glucose) are dissolve in water and allow to stand for some time. The specific rotation of
solution changes gradually until a final value of + 53º is reached. This change in optical rotation of solution of
either form until a constant value is called mutarotation
It froms fructose pentaacetate with acetyl chloride
Haworth projection : Fructofuranose
Haworth projection : Fructofuranose
When it is hydrolysed with dilute acids or by the enzyme maltase, maltose yields two
molecules of D (+)-glucose. Maltose is a reducing sugar, e.g., it reduces Fehling’s solution
it forms an oxime and an osazone, and undergoes mutarotation. This indicates that at
least one aldehyde group (of the two glucose molecules) is free in maltose.
Lactose
Starch is the main contributor of carbohydrates in our diet. It exists exclusively in plants, stored in the seeds,
roots, and fibres as food reserve. Example rice, potato
Cellulose is the main structural material of tree and other plants. Wood is 50% cellulose, while
cotton wool is almost pure cellulose. Other sources of cellulose are straw, corncobs, bagasse, and
similar agricultural wastes
Each living cell is made up of thousands of different proteins All proteins contain the elements like carbon,
hydrogen, oxygen, nitrogen and sulphur. Some of these also contain phosphorus, iodine and traces of metals
Amino acids are the building blocks of the molecular structure of the important and
very complex class of compounds known as proteins. The proteins on hydrolysis
yield mixture of the component amino acids.
Zwitter ion (Dipolar Nature of Amino acids)
When an ionised amino acid is placed in an electric field, it will actually migrate towards the
opposite electrode. Depending upon the pH of the medium, three things can happen
The pH at which the amino acid shows no tendency to migrate when placed in an electric field is known as its
isoelectric point
Isoelectric Table
General methods of preparation
Formaldehyde reacts with amino acids to form N-methylene amino acids. In this reaction basic character is lost
and thus, free acid can be determined by titration - Sorenson titration method for amino acids
Other Reactions of a Amino Acid
Zwitter ion formation in amino acids
Peptides (Proteins) Peptides (Proteins) may be defined as condensation polymers of a-amino acids
and having peculiar overall structure which determines their specific physiological functions in the living organism.
Proteins are the most abundant-biomolecules of the living beings. The chief source of proteins are milk, cheese,
pulses peanuts, fish meat etc. These are high molecular mass complex, biopolymers of amino acids. They
occur in every part of the body and form fundamental basis of structures and determine functions of life. The word
protein is derived from Greek word proteios which means primary or of prime importance
Simple proteins : These proteins on hydrolysis give only a-aminoacids. For example albumin
in the white portion of eggs, glutenin in wheat, oxygenin in rice, keratin in hair, nails horns etc
Proteins are biopolymers obtained by condensation of large number of amino acids through peptide bonds
having three dimensional (3D) structures. Structure and shape of proteins can be studied at four different levels
i.e. primary, secondary, tertiary and quarternary, each level being more complex than the previous one
The tertiary structure of protein represent overall folding of the polypeptide chains i.e further
folding of the secondary structure. In other words, tertiary structure refers to the manner in
which the entire protein molecule folds up in the three dimensional space to produce a specific
shape. It gives rise to two major molecular shapes fibrous and globular
Although many proteins exist as a single polypeptide chain but there are certain proteins which are
composed of two or more polypeptide chains referred to as sub-units or protomoss. These subunits may
be identical or different and are held together by non-polar covalent forces such as, H-bonds, vanderwaals
interaction and electrostatic interactions
A protein found in a biological sytem having a unique three dimensional structure and specific
biological activity is called a native protein. When a protein in its native form is subjected to a
physical change like change in temperature or pH, the hydrogen bonds are disturbed. As a
result-globules unfold and helices get uncoiled and protein loses its biological activity. This is
called Denaturation of proteins
Enzymes Nitrogenous complex compounds with basic nature are called Enzymes. Enzymes are biological
catalysts. All biological reactions are catalysed by enzyme. enzyme lower the activation energy thereby increasing
the rate of the reaction.
(i) Specificity : Each enzyme catalyses only one chemical reaction.
(ii) Efficiency : Enzymes are very efficient catalyst. They increase the rate of reaction by 10 times.
(iii) Small quantity :- Only small amount of enzyme can be highly efficient because. They are regenerated after
their catalytic activity
Definition Vitamins may be defined as a group of biomolecules which are required in small amounts for
normal metabolic process and for the life, growth and health of human beings and animal organisms
Nucleic acids were first discovered by a Swiss biochemist, Friedrich Miescher (1869) who called them nuclein
due to their acidic nature.
Chemical analysis of chromosomes shows presence of two nucleic acids-DNA (Deoxyribo nucleic acid) and
RNA (Ribo nucleic acid)
J.D. Watson and F.H.C. Crick (1953) proposed double helical structure of DNA based on the results of
M.H.F.Wilkins and co-workers. All these three persons were awarded Nobel Prize in 1962 for this work.
The following are some of the characteristic features of double helical structure of DNA.
(1) r-RNA (Ribosomal – RNA) It is found in the ribosomes and it is usually associated with protein to form
the ribosomes. It is synthesised in the nucleus by DNA. It is single stranded, comprising about 80% of the total
RNA. It is metabolically stable
These are very high molecular mass substances where each molecule is derived from very large number of
simple molecules joined together in a regular way. This simple molecule is monomer and the process of formation
of polymers from simple molecule is polymerization.
Polymers can be classified by following ways
It is obtained by polymerization of vinyl chloride. PVC is used in the manufacture of imitation leather, floor
covering, corrugated roofing material, and gramophone records
Some polymers and their uses
Some commercially Important Polymers
A large number of polymers are quite resistant to the environmental degradation processes and are thus responsible
for the accumulation of polymeric soild waste materials. These soild wastes cause acute environmental problems
and remain undegraded for quite a long time. In view of the general awareness and concern for the problems
created by the polymeric soild wastes, certain new biodegradable synthetic polymers have been designed and
developed. These polymers contain functional groups similar to the functional groups present in biopolymers.
Aliphatic polyesters are one of the important classes of biodegradable poylmers. Some examples are given
below
