Page 16 - Lesson Notes - Biomolecules 1

two types of monosaccharide monomers, e.g., Chitin, pectin, peptidoglycans
(murein), hyaluronic acid.
iii. One ofthem is explained below Chitin
It is the second most abundant natural polymer, found in exoskeleton of arthropods
(e.g., prawns, crabs, etc.) and in cell wall of fungi. It has building blocks of amino
sugars and chemically modified sugar.
iv. acetylglucosamine units interlinked by glycosidic bond
Glucosamine also acts as building block (like N-acetyl glucosamine) in other types of
heteropolysaccharide.
Functions of Polysaccharide
Polysaccharide plays multiple function and can be used in the following ways
(i) Acts as structural compounds in cell wall of plants certain fungi and protists, e.g.,
Cellulose, chitin.
(ii) Helps in anticoagulation and prevents blood clotting inside the vessels, e.g.,
Heparin.
(iii) Helps in lubrication of joints between bones, e.g., Hyaluronic acid.
(iv) Also used in tissue culture, e.g. Agar.
(v) Acts as a reserve food, e.g., Starch.
Nucleic Acids
The other type of macromolecule found as a part of acid insoluble fraction of any
living tissue is the nucleic acids. These are polymeric compounds of nucleotides, i.e.,
polynucleotides.
A nucleotide (as discussed previously in the chapter) is composed of three
chemically distinct components
(i) Heterocyclic compound-nitrogen base (adenine, guanine, uracil, cytosine and
thymine).
(ii) Monosaccharide (ribose or deoxyribose).
(iii) Phosphoric acid or phosphate.
A nucleic acid which contains deoxyribose sugar is called deoxyribonucleic acid
(DNA), while that which contains ribose sugar is ribonucleic acid (RNA).
Deoxyribonucleic Acid (DNA)
DNA is genetic material found in the nucleus of all living cells except some viruses.
In eukaryotic organisms linear DNA is found in nucleus, in the mitochondria and
chloroplasts, whereas in prokaryotes, DNA is circular in structure and is found in the
cytoplasm.
Structure of DNA
The structure of DNA was elucidated by Watson and Crick based on X-ray diffraction
studies. They proposed a double helix model of DNA. According to this model, DNA
exists as a double helix and consists of two strands of polynucleotides that are
antiparallel to each other, i.e., both run in opposite directions, one in 5′–> 3′ direction
and other in 3’—> 5’direction. ,