The primary structure of a protein is what is encoded in the DNA.
All other protein structures involve folding of the protein, chemical interactions within the protein, and protein-protein interactions. This lesson describes primary protein structure.
What Is the Primary Structure of a Protein?
By definition, the primary structure of a protein is the linear sequence of amino acids. Together, this linear sequence is referred to as a polypeptide chain. The amino acids in the primary structure are held together by covalent bonds, which are made during the process of protein synthesis (translation).The primary structure of a protein is encoded in your DNA. In order to make a protein, you must first make a copy of the DNA.
This process is called transcription. This copy is called mRNA. The copy is sent out of the nucleus to the cytoplasm. Once in the cytoplasm, ribosomes will interact with the mRNA. They can read the mRNA sequence and create a protein (polypeptide) from individual amino acids.
This process is called translation.
What Are the Pieces of a Polypeptide Chain?
A polypeptide chain is a string of amino acids (residues) linked together by chemical bonds. Each individual amino acid consists of a backbone part that is present in all the amino acid types. The sequence of molecules is always nitrogen-carbon-carbon. The middle carbon has a side group attached to it.
The side group is unique to each type of residue and gives each amino acid its name. Examples are valine, proline, and glutamic acid.Polypeptide chains have two ends. The beginning of a polypeptide is called the amino terminus (N-term).
It has this name because the molecule on the very end is nitrogen. The end of a polypeptide is called the carboxy terminus (C-term). It has this name because the molecule on the very end is carbon.
Counting of residues always starts at the N-term.DNA encodes the primary structure of a protein. The process of creating a protein from DNA is called the central dogma. In this process, a gene (a specific sequence of nucleotides) is first transcribed into mRNA. Unlike DNA, mRNA can leave the nucleus and enter the cytoplasm.
Once in the cytoplasm, mRNA is read by the ribosome in a process called translation. When the protein is translated from mRNA, it is created from N-term to C-term. In addition, the sequence of a protein is unique to that protein.
The sequence also defines the structure and function of the protein.Each protein is made up of a string of amino acids. There are twenty different amino acids. These amino acids are linked together by a chemical reaction. This reaction is called a dehydration reaction because one water molecule is lost in the process. Proteins can be modified after they are translated (post-translational modifications). These include disulfide formation, phosphorylations, and glycosylations.
These modifications are usually considered a part of the primary structure.
The process of creating a protein is called the central dogma. It has two steps.
The first is creating a copy of the DNA (transcription) and the second is creating a protein from the DNA copy (translation). Once a protein is created, it can undergo post-translational modifications. These modifications can be the addition of chemical groups to certain amino acids. This is determined by the amino acid and not encoded in the DNA.