BBC Science Focus

EXPANDING THE GENETIC ALPHABET

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Adding additional building blocks to the DNA of E.coli bacteria has enabled researcher­s to create synthetic life forms capable of producing entirely new types of protein. Here’s how they did it…

PROTEINS are large, complex molecules that are essential for life. They perform many different tasks inside our bodies such as acting as antibodies, transporti­ng smaller molecules within cells, and transmitti­ng signals to coordinate biological processes between different organs. They also help form many of the body’s intricate structures, such as hair, skin and muscle.

There are hundreds of thousands of different proteins in the human body and many, many millions more throughout the natural world. Difference­s in our genes causes variation in the proteins our cells produce, which leads to diversity in our physical characteri­stics.

Proteins are formed when small organic compounds called AMINO

ACIDS link together in long chains There are only 20 naturally occurring amino acids but each protein molecule contains hundreds of them joined together in a unique sequence. This gives each protein its own individual properties.

Each strand of DNA is made from chemicals known as BASES. There are four different bases – thymine, adenine, guanine and cytosine. The two strands that make up DNA’s double helix are joined together by chemical crosslinks between the different bases. Thymine always pairs with adenine, and guanine with cytosine. However, the Scripps team created two new bases: X and Y. The order of the bases running along the strands forms a chemical code or set of instructio­ns for creating proteins. Each section of DNA that codes for a particular protein is called a GENE.

The process of manufactur­ing a protein has two major steps. First, informatio­n in the DNA needed to make a specific protein is transferre­d to an mRNA (messenger RNA) molecule by a process known as transcript­ion. During this process, thymine ( T) is converted to uracil (U). A second type of RNA, tRNA (transfer RNA) picks up specific amino acids and returns them to the mRNA. The amino acids are lined up according to instructio­ns on the mRNA and join together to form a protein.

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