CBSE · Class 12 · Biology · Biotechnology and its ApplicationsWhat are transgenic animals? Give four major reasons why we study transgenic animals and explain how human insulin (Humulin) is produced using recombinant DNA technology.

Definition of Transgenic Animals\nAnimals that have had their DNA manipulated to possess and express an extra (foreign) gene are known as transgenic animals. Transgenic rats, rabbits, pigs, sheep, cows, and fish have been produced, although the vast majority of transgenic animals are mice.

Four Major Reasons for Studying Transgenic Animals

1. Normal Physiology and Development: Transgenic animals can be used to study how genes are regulated and how they affect the normal functioning of the body and its development. For example, studying the complex factors involved in growth such as insulin-like growth factor.
2. Study of Disease: Many transgenic animals are designed to increase our understanding of how genes contribute to the development of disease. These serve as models for human diseases such as cancer, cystic fibrosis, rheumatoid arthritis, and Alzheimer's.
3. Biological Products: Transgenic animals can be made to produce useful biological products by introducing a portion of DNA (or genes) which codes for a particular product such as human protein alpha-1-antitrypsin used to treat emphysema.
4. Chemical Safety Testing: This is known as toxicity/safety testing. Transgenic animals are made that carry genes which make them more sensitive to toxic substances than non-transgenic animals. Toxicity testing in such animals allows us to obtain results in less time.

Production of Human Insulin (Humulin)\nInsulin used for diabetes was previously extracted from the pancreas of slaughtered cattle and pigs. However, this caused allergic reactions in some patients. Recombinant DNA technology solved this problem:

• Insulin consists of two short polypeptide chains: Chain A and Chain B, linked together by disulphide bridges.
• In mammals, insulin is synthesized as a pro-hormone containing an extra stretch called the C-peptide, which is removed during maturation.
• In 1983, an American company Eli Lilly prepared two DNA sequences corresponding to A and B chains of human insulin and introduced them into plasmids of E. coli to produce insulin chains separately.
• Chain A and Chain B were produced separately, extracted, and combined by creating disulfide bonds to form functional human insulin (Humulin).