Transcription and Translation: Making proteins from DNA

April 2010
Written by Hana Kucera

Proteins are responsible for some of the most important functions in a cell. The instructions for making proteins exist as DNA sequence on the chromosomes of living things. There are several steps needed to convert these instructions into a protein molecule. The first step is transcription, in which DNA sequence is read and messenger RNA is produced. In eukaryotes, the second step is called post-transcriptional processing and involves preparing the mRNA for the third step, translation. During translation, the message on the RNA molecule gets converted into an amino acid sequence. The process of information transfer from DNA to RNA to protein is called “The Central Dogma of Molecular Biology.”

The information on chromosomes is determined by the order in which the individual nucleotides are found on the DNA. The genetic code is a set of rules that dictate which amino acids make up each particular protein. Think of the genetic code as the language that is used to convey biological information. Within this code, a group of three nucleotides is called a codon, and many codons in a row make up a gene. Think of the nucleotides as the letters in the alphabet of this biological language, and the codons as words. Genes, then, would be entire sentences, and chromosomes would be books. Each chromosome has many genes on it, and each gene codes for a particular protein. RNA acts as a “middle-man” messenger that works to convert the DNA information into protein.


 

Transcription
Transcription is the process of converting DNA sequence information into messenger RNA molecules. A number of enzymes work together to read the DNA molecule and produce the mRNA.  This process is called transcription because it can be thought of as analogous to when court transcribers write down what is said in court—the information is still in the same language (English) but in a different format (written instead of spoken). Think of transcription as information staying in the same language (nucleic acids) but being converted to a different format (RNA instead of DNA).

Post-transcriptional processing
In eukaroytes, after transcription, the RNA is still not ready to be translated into a protein. The mRNA message that codes for the protein product contains regions of RNA that interrupt the protein message and need to be removed. These interrupting regions are called introns. During post-transcriptional processing, introns are removed and the two ends of the mRNA are modified to help with the translation process. One end gets a special addition called a 5’ cap and on the other end, a large number of adenosines are added. These additions protect the mRNA from being broken down from either end, help with exporting the mRNA from the nucleus and help with the next step, translation. Prokaryotes do not have any of these post-transcriptional modifications.

Translation
Translation is the process of converting RNA sequence information into protein sequence.  In this case, transfer and ribosomal RNA work in concert to read the mRNA message, bring amino acids together and form a protein polymer. This process is called translation because it is similar to translation between languages. Think of it as translation from the language of nucleic acids to the language of proteins.

Read more about Transcription

Read more about Translation