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A Handbook of Biology

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FÜÑÇTÏØÑS ØF

PRØTËÏÑS

For growth and tissue repair.

Transport nutrients across cell membranes

(e.g. GLUT-4 enables glucose transport into cell).

Acts as intercellular ground substance (e.g.

collagen).

Acts as antibodies to fight infectious

organisms.

Acts as receptors (e.g.receptors of smell,

taste, hormones). Some are hormones (e.g.

Insulin), enzymes (e.g. trypsin), pigments

(e.g. hemoglobin) etc.

KNOWLEDGE CORNER

Most abundant protein in animal world: Collagen.

Most abundant protein in the biosphere: Ribulose

bisphosphate carboxylase - oxygenase (RuBisCO)

(NEET 2020)

STRÜÇTÜRÅL LËVËLS ØF PRØTËÏÑ



Primary structure: It describes the sequence of amino acids, i.e. the

positional information in a protein. Left end of the chain has first amino

acid (N-terminal amino acid). Right end has last amino acid (C-terminal

amino acid).

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Secondary structure: Here, a polypeptide chain is folded in the form of

α-helix or β- pleated sheets. Proteins have only right- handed helices.

E.g. Keratin, Fibroin (silk fibre).