If you want to pick out a biomolecule to be called as an “all-rounder” then it is undoubtedly proteins. Proteins are the biomolecules that can play many roles inside a cell. It is the workforce inside the cells and has many functions.
Proteins are made up of 20 different kinds of amino acids joined by co-valent linkages called peptide bonds. Even though more than 300 amino acids are known, only 20 are called as standard amino acids as it is present in almost all cells.
Classification of Proteins based on Function
1. Proteins are enzymes: Enzymes are biological catalysts involved in almost all biological reactions. Enzymes speed up the biological reactions by lowering activation energy without undergoing any change. Nearly all enzymes are globular proteins.
Examples: protease, amylase, catalase, lipase etc
2. As structural proteins: Usually inert to biological reactions.
- Collagen is a structural protein and the most abundant protein in animals
- Keratin, is a structural protein in nails, hair, feather, tortoise shell etc
- Fibroin in spider webs
- Resilin in wing hinges of some insects
3. Transport proteins or carrier proteins
It is involved in the transport of essential biological factors or molecules to various parts of organisms.
- Hb of RBC carries oxygen to different tissues
- Blood plasma contains lipoproteins, which carry lipids from liver to other organs
- Ceruloplasmin, a transport protein transport copper in blood
4. Nutritional or storage proteins
- ovalbumin in egg white
- Casein a milk protein
- Ferritin stores Iron in bacteria, some plants and animal tissues
5. Proteins in movement: contractile or motor proteins
- Actin and myosin function in contractile system of skeletal muscles
- Tubulin in microtubule
6. Defense proteins: Antibodies involved in the immune response are proteins.
- Fibrinogen and thrombin are blood clotting proteins that prevents loss of blood on injury
7. Regulatory proteins: Many proteins are involved in signal transduction. Peptide hormones are present and regulates cellular and physiological activity.
- Insulin regulates sugar metabolism
- G proteins in signal transduction pathway
- GH for bone growth
8. Toxic proteins: Function is defence
- Snake venom, bacterial toxins, plant proteins like ricins.
Thus with amazing diversity in function, proteins are the most abundant bimolecule in a cell.