Although most genetic information is stored in the nucleus of eukaryotes, protein synthesis takes place in cytoplasmic ribosomes, either as free ribosomes or on the rough endoplasmic reticulum. The genetic information in the nucleus must be transmitted to these ribosomes in order for protein to be produced. mRNA is responsible for this (messenger ribonucleic acid). It’s extremely similar to DNA, but there are two key differences.

• In mRNA, the nucleotide uracil replaces the base thymine in DNA.
• In DNA, the sugar deoxyribose is replaced by mRNA’s sugar ribose.

The double helix shape of DNA uncoils at the start of protein synthesis, much like it does during DNA replication, allowing mRNA to duplicate the genetic sequence responsible for coding a specific protein. The DNA has uncoiled at the start, allowing the enzyme RNA polymerase to enter and transcribe (copy) the genetic material into mRNA.

If the coding strand of DNA is G-G-C-A-T-T, then the template strand would be G-G-C-A-T-T. The mRNA would be G G C A U-U and the codon would be C C G T T A. (remembering that uracil replaces thymine). The mRNA strand travels out of the nucleus and away from the DNA, towards the ribosomes, now that the genetic information required to create substances is available on the mRNA strand.