Complex of (Arginyl-tRNA synthetase/tRNA/Arginine)
Saccharomyces cerevisiae (Baker's yeast)
Proteins are some of the most important ingredients of life. Instructions on how to make specific proteins is stored in the sequence of the DNA. From DNA sequence to the amino acid sequence of the protein is a long way involving several intermediate steps. Most of the intermediate steps involved RNA, ribonucleic acids. RNA and DNA both contain a backbone made from five-membered sugar rings (pentose) connected by phosphate groups. The bases are attached to one atom of the sugar. DNA uses four types of bases and RNA also uses three of them, but uses the uracil base instead of the thymine base. The most important difference however is the addition of one extra oxygen to the sugar in the RNA backbone. In that position DNA has a hydrogen atom only and is missing the oxygen, which is why it is called deoxy (without oxygen). Proteins translate the DNA genetic code into a corresponding RNA genetic code, creating messenger RNA (mRNA). This step is called transcription. In the next step the information of the mRNA is used to create proteins. This step is called translation and takes place in a very large assembly of RNA and proteins called ribosome. One of the helper molecules for this process is the transfer RNA (tRNA).
It has a peculiar clover-leaf structure and on one of it loops, the anticodon loop which is complementary to the 3-base sequence on the mRNA. tRNA forms a complex with an amino acid corresponding to the code in the anticodon loop. When the tRNA-amino acid complex binds to the mRNA being read by the ribosome, a chemical reaction attaches it to the growing polypeptide chain of the protein. For each tRNA type there is one corresponding amino acid type. The amino acid is attached to the tRNA by a protein called an amino-acyl-tRNA synthetase. That is the molecule which you see here. Again, there is one type of synthetase for each type of amino acid. The one here is specific for the amino acid arginine. The structure shows the protein as a ternary complex, that is the protein itself, the tRNA and arginine. Once the synthetase has completed its task of attaching the amino acid to the tRNA, the tRNA with bound amino acid is released from the complex, ready to travel to its next destination, the assembly line called ribosome.
Protein Data Bank (PDB)
author: Arno Paehler