For example, consider a tetrapeptide having N-terminal valine, glycine, methionine and a C-terminal leucine is sequenced as follows All the amino acids are sequenced or numbered from the N-terminal to the C-terminal of the peptide chain. While sequencing the amino acids in a peptide chain, the N-terminal is written on the left side while the C-terminal is written on the right side. These ends are known as N-terminal and C-terminal respectively. The peptide chain formed as a result of peptide bonds have a free amino group at one end and a free carboxylic group at the other end. In a peptide chain, only the terminal carboxylic and amino groups and the groups present in the side chains of amino acids can accept or release electrons at the physiologic pH of our body. However, a peptide bond is polar in characteristic due to highly electronegative atoms (O and N)and thus takes part in the formation of hydrogen bonds. The carbonyl and the amide groups present in the peptide bond do not release or accept electrons and remain unchanged at the physiologic pH. This rigid characteristic of the peptide bond prevents the free rotation of groups around it. It is shorter and rigid than a typical single covalent bond. The peptide bond is considered to have partial characteristics of a double bond. One amino acid is determined by a collection of three nucleotides known as genetic code. The sequence of amino acids in a polypeptide chain is dependent on the sequence of nucleotides in the gene encoding the protein. Thus, it can also form additional peptide bonds at both of its ends.Īll the amino acids present in a protein are together linked and sequenced via peptide bonds to form long linear chains. The resultant dipeptide also has a free amino group on one end and a free carboxylic group on the other end. It is a covalent bond that is formed when the carboxylic group of one amino acid reacts with the amino group of another amino acid. All the properties and functions of a protein are dependent on the sequence of amino acids in the peptide chains present in it.Īt the level of primary structure, we study the sequence of amino acids that are linked via peptide bonds in the polypeptide chains present in a protein. This is the basic level of protein structure. Primary StructureĪt this level of protein structure, the sequence of amino acids in proteins is studied. In this article, we will study these four levels of protein structure. In order to understand this complexity, the structure of proteins is studied at four levels of organization: Rather, the chains of amino acids are arranged to form molecules having complex structures. The amino acids present in these long chains determine the final structure, properties, and functions of proteins.Īmino acids in proteins don’t lie in linear chains. These amino acids are linked together via peptide bonds in the form of long chains. Proteins are the organic molecules made up of amino acids.
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