Protein assembly continues until the ribosome encounters a “stop” codon (a sequence of three nucleotides that does not code for an amino acid).
(Amino acids are the building blocks of proteins.) A type of RNA called transfer RNA (tRNA) assembles the protein, one amino acid at a time. Each sequence of three nucleotides, called a codon, usually codes for one particular amino acid. The mRNA interacts with a specialized complex called a ribosome, which "reads" the sequence of mRNA nucleotides. Translation, the second step in getting from a gene to a protein, takes place in the cytoplasm. The type of RNA that contains the information for making a protein is called messenger RNA (mRNA) because it carries the information, or message, from the DNA out of the nucleus into the cytoplasm. Both RNA and DNA are made up of a chain of building blocks called nucleotides, but they have slightly different chemical properties. Together, transcription and translation are known as gene expression.ĭuring the process of transcription, the information stored in a gene's DNA is passed to a similar molecule called RNA (ribonucleic acid) in the cell nucleus. It consists of two major steps: transcription and translation. (A few genes produce regulatory molecules that help the cell assemble proteins.) The journey from gene to protein is complex and tightly controlled within each cell. Most genes contain the information needed to make functional molecules called proteins.
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