How are DNA sequences used to make proteins?

The instructions for making proteins are encoded within DNA sequences. They are found in short sequences of DNA called codons. 

The process of reading the instructions in the DNA sequences and using them to build proteins is highly complex and takes place over two major steps – transcription and translation.  

Transcription, which is the first step, takes place in the cell’s nucleus. During this step, the information stored in the gene’s DNA is copied into RNA (ribonucleic acid), a similar molecule in the cell nucleus. DNA and RNA are both composed of a chain of building blocks called nucleotides but their chemical properties are slightly different from each other. mRNA (messenger RNA), which is the specific type of RNA that contains the information for making a protein, carries the information from the DNA out of the nucleus into the cytoplasm.  

Translation, which is the second step, takes place in the cytoplasm. During this step, the mRNA that’s carrying the protein-making information, interacts with a specialized complex called a ribosome. The ribosome reads the sequence of mRNA nucleotides and converts the long string of codons into a long string of amino acids, which are the building blocks of proteins. Each string of amino acids arranged in a particular order codes for a specific protein. In the final step, tRNA (transfer RNA) assembles the protein one amino acid at a time, until the ribosome encounters a ‘stop’ codon, which is a sequence of 3 nucleotides that does not code for an amino acid.