Gene expression: from DNA to protein

0:00How does the code in a gene become a protein?

0:04In our cells, most DNA is kept in the nucleus, but proteins are made in the cytoplasm.

0:11A gene is a section of DNA that codes for one protein.

0:16Its code is the order of four bases. Across the strands, A pairs with T, and C with G.

0:24Step one is transcription. The gene's two strands separate, and one acts as a template.

0:31RNA bases pair with it, but RNA has uracil, U, instead of thymine, T, so U pairs with A.

0:41They join into a single strand of messenger RNA, or mRNA, a copy of the gene's code.

0:48The mRNA leaves the nucleus through a small hole called a pore.

0:54Step two, translation, happens at a ribosome, which builds proteins from units called amino acids.

1:03The ribosome reads three bases at a time. Each group of three is a codon.

1:09The first codon, A U G, adds the amino acid methionine.

1:15Then G C U adds alanine, and G G A adds glycine, building a chain.

1:22A real chain usually has hundreds of amino acids. Once finished, it folds into a protein.

1:31It could be an enzyme, which speeds up reactions, or keratin, in hair and nails.

1:37Nearly all your cells have the same genes, but each type switches on only some of them.

1:44That is why a muscle cell is so different from a nerve cell.

1:48Transcription copies a gene into mRNA, then translation reads it, codon by codon, to build a protein.