How do genes direct the production of proteins?
The journey from gene to protein is a complex, two-step process known as gene expression, consisting of transcription and translation.
The Process of Gene Expression
Most genes contain the information needed to make functional molecules called proteins. The flow of information from DNA to RNA to proteins is a fundamental principle of molecular biology, sometimes called the “central dogma.” This process occurs in two major steps:
1. Transcription
During transcription, the information stored in a gene's DNA is passed to a similar molecule called RNA (ribonucleic acid) in the cell nucleus. Both RNA and DNA are made of building blocks called nucleotides. The specific type of RNA that carries the information for making a protein is called messenger RNA (mRNA), which transports the message from the DNA out of the nucleus and into the cytoplasm.
2. Translation
Translation takes place in the cytoplasm. The process involves the following:
- The mRNA interacts with a specialized complex called a ribosome, which reads the sequence of mRNA nucleotides.
- Each sequence of three nucleotides, called a codon, usually codes for one particular amino acid.
- A type of RNA called transfer RNA (tRNA) assembles the protein one amino acid at a time.
- Protein assembly continues until the ribosome encounters a “stop” codon, which does not code for an amino acid.