A polymer of amino acids connected by peptide bonds is referred to as a protein structure. Protein structure is when the peptide backbone of the protein structure will fold into itself, to give proteins their unique shape. This folding of the polypeptide chains happens due to the interaction between the carboxyl groups along with the amine groups of the peptide chains.
What is the secondary structure of protein?
It refers to local folded structures that form within a polypeptide due to interactions between atoms of the backbone.
- The proteins do not exist in just simple chains of polypeptides.
- These polypeptide chains usually fold due to the interaction between the amine and carboxyl group of the peptide link.
- The structure refers to the shape in which a long polypeptide chain can exist.
- They are found to exist in two different types of structures α – helix and β – pleated sheet structures.
- This structure arises due to the regular folding of the backbone of the polypeptide chain due to hydrogen bonding between -CO group and -NH groups of the peptide bond.
- However, segments of the protein chain may acquire their own local fold, which is much simpler and usually takes the shape of a spiral, an extended shape or a loop. These local folds are termed secondary elements and form the protein’s secondary structure.
Different kinds of shapes formed in the secondary structure.
There are two kinds of shapes formed in the secondary structure.
- α-helix: The backbone follows a helical structure. The hydrogen bonds with the oxygen between the different layers of the helix, giving it this helical structure.
- β-pleated sheet: here the polypeptide chains are stacked next to each other and their outer hydrogen molecules form intramolecular bonds to give it this sheet-like structure
Rules of Protein Structure
- The type determines the function of a protein.
- A protein’s shape is determined by its primary structure (the amino acid sequence).
- The amino acid sequence within a protein is determined by the encoding sequence of nucleotides in the gene (DNA).
About Protein Structure
Linderstrom-Lang (1952) in particular first suggested a hierarchy of protein structure with four levels: central, secondary, tertiary , and quaternary. You are already familiar with this hierarchy, because the most useful starting point for teaching basic protein structure is this structural grouping.
- The primary structure of protein is the hierarchy’s basic level, and is the particular linear sequence of amino acids comprising one polypeptide chain.
- Secondary structure is the next level up from the primary structure, and is the regular folding of regions into specific structural patterns within one polypeptide chain. Hydrogen bonds between the carbonyl oxygen and the peptide bond amide hydrogen are normally held together by secondary structures.
- Tertiary structure is the next level up from the secondary structure, and is the particular three-dimensional arrangement of all the amino acids in a single polypeptide chain. This structure is usually conformational, native, and active, and is held together by multiple noncovalent interactions.
- Quaternary structure is the next ‘step up’ between two or more polypeptide chains from the tertiary structure and is the specific spatial arrangement and interactions.
Proteins’ Classification
Proteins are divided into two categories based on their molecular form.
- Fibrous Proteins: Fibrous proteins are proteins that are made up of fibres.
The fibre-like structure is generated when the polypeptide chains run parallel and are kept together by hydrogen and disulfide bonds. In most cases, these proteins are water insoluble. These are proteins that aren’t soluble in water.
Example;Keratin (found in hair, wool, and silk) and myosin (found in muscles), for example
- Globular Proteins: This structure is formed when polypeptide chains coil around each other to form a spherical shape. These are frequently water soluble.
Example-Insulin and albumin, for example, are examples of globular proteins.
Conclusion
Biological polymers are what we refer to as proteins (i.e. they occur naturally in nature). Amino acids are the building components of proteins, as we previously learned. Proteins have a lengthy chain-like structure, with amino acids as the major constituent. Peptide bonds join these amino acids, and a polypeptide chain is formed when several of these bonds bind together. A protein is created when one or more of these polypeptide chains twist or fold spontaneously.