The Structure & Function of a mRNA

Ribonucleic acid, or RNA, is one form of genetic material. DNA is the genetic material that holds genetic coding. RNA is the genetic material that allows the coding in DNA to be transformed into proteins. There are many different types of RNA including messenger RNA or mRNA, ribosomal RNA or rRNA, and transfer RNA or tRNA. Messenger RNA copies the code from DNA and takes it out into the cell, where it can be translated and used to make a protein. RNA is found in most cells and viruses.

Building Blocks of RNA

• All three types of RNA have the same basic building blocks. There are four bases: Adenine (A), Guanine (G), Cytosine (C) and Uracil (U). This is very similar to the bases of DNA: Adenine, Guanine, Cytosine and Thymine. In DNA, which is double stranded, Guanine pairs with Cytosine and Adenine pairs with Thymine. RNA is single-stranded, so when it makes a copy of the DNA, Guanine pairs with Cytosine and vise verse, Adenine pairs with Thymine, and Uracil pairs with Adenine.

Structure

• The structure of mRNA includes more than simply a copy of the gene from the DNA. On one end of the mRNA is a cap. This is a structure that allows the mRNA to bind to the ribosome and is very important in protein synthesis. Then there is a section of RNA that is non-coding. This section can vary in length. Next is an initiation codon, which signals the beginning of the coding sequence. Finally, there is the coding region which contains the copy of the genes.

mRNA and Protein Synthesis

• DNA carries the genetic code and the copy of all proteins made in the body. The first step in protein synthesis is for a copy of the gene to be made in the form of mRNA. This process is called transcription. When the copy is complete, the mRNA travels out of the cell nucleus and into the cytoplasm of the cell. The mRNA then connects with the ribosome, which is made of rRNA. The next step is for tRNA to string together the amino acids coded by the mRNA. This is called translation. When the end of the coding sequence on the mRNA is reached, the final amino acid is added and the protein is complete.

Genetic Code

• The genetic code is found in the sequence of nucleotides and can be expressed as either DNA codons or RNA codons. RNA codons are found specifically in mRNA. The genetic code or RNA codons are found in the triplets of nucleotides (A, G, C, and U) in various combinations. Each combination codes for one of the 20 amino acids. This is the code that tells the tRNA which amino acid to connect to the chain to create the protein.

Breakdown of mRNA

• The lifespan of a strand of mRNA is very short and can range from a couple of minutes to a couple of days. The mRNA is constantly broken down to its individual nucleotides by ribonucleases. This is unlike the other forms of RNA (rRNA and tRNA) which are much more stable. In some cases, the mRNA that has been translated is already broken down before the complete protein is made.