The term biotechnology refers to the use of living organisms or their products to modify human health and their human environment. For example, 'testtube' programme, synthesis of a gene or correcting a defective gene are all part of the biotechnology. The basis of the modern biotechnology are genetic engineering and maintenance of sterile conditions. Genetic engineering is the technique that alter the chemistry of genetic material i.e. DNA and RNA, then this genetic material is introduced into host organisms, which alter the phenotype of the host organism.
Discovery of _molecule made genetic engineering possible.

Options

A. Restriction exonuclease
B. Restriction exonuclease
C. Ribozyme
D. DNA polymerase

Explanation

**Step-by-Step Solution:**

1. **Understanding Biotechnology**: The term biotechnology encompasses the use of living organisms or their products to enhance human health and the environment. This includes various applications such as gene synthesis and correction of genetic disorders.

2. **Role of Genetic Engineering**: Genetic engineering is a crucial aspect of modern biotechnology. It involves altering the genetic material (DNA or RNA) of an organism, which can lead to changes in the organism's phenotype.

3. **Importance of Sterile Conditions**: Maintaining sterile conditions is essential in biotechnology to prevent contamination and ensure the success of genetic manipulation.

4. **Mechanism of Genetic Engineering**: The process of genetic engineering involves manipulating DNA. This includes cutting specific parts of DNA, which is facilitated by enzymes known as restriction endonucleases.

5. **Discovery of Key Molecule**: The question asks about the discovery of a molecule that made genetic engineering possible. The key molecule in this context refers to restriction endonucleases, which are enzymes that can cut DNA at specific sequences.

6. **Conclusion**: The discovery of restriction endonucleases is what enabled the techniques of genetic engineering, allowing scientists to manipulate DNA and introduce it into host organisms to alter their genetic makeup.

**Final Answer**: The discovery of restriction endonucleases made genetic engineering possible.

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