Lesson 6 of 14 · 5 min
Proteins
NCERT §9.4
Kabir asks Farah to name one thing protein does in her body. She says 'builds muscle'. He says that is one job out of many, and starts listing.
The lesson in notes
In short
Proteins are polypeptides: linear chains of amino acids joined by peptide bonds.
Since a protein is built from up to 20 types of amino acid, it is a heteropolymer. A homopolymer has only one type of monomer repeated n times.
Some amino acids are essential: the body cannot make them, so they must come from food, and dietary proteins are their source. Non-essential amino acids are those the body can make.
Proteins do many jobs: some carry nutrients across the cell membrane, some fight infectious organisms, some are hormones and some are enzymes.
Examples from NCERT's table: collagen makes up the ground substance between cells, trypsin is an enzyme, insulin is a hormone, antibodies fight infectious agents, receptors sense smell, taste and hormones, and GLUT-4 lets glucose into cells.
Collagen is the most abundant protein in the animal world. RuBisCO (ribulose bisphosphate carboxylase-oxygenase) is the most abundant protein in the whole biosphere.