Peptides VS Proteins

Peptides and proteins are natural and essential organic compounds in cells.They’re all made up of amino acids.Amino acids are naturally occurring compounds that join together to form peptides, polypeptides, and proteins.Each amino acid contains an amine (-nh 2) and an oh (-cooh), as well as specific side chains (R groups).Side chain groups vary in size, shape, charge, and reactivity, so each amino acid is unique.There are 20 single amino acids that can be joined together in different combinations, thus giving rise to a diversity of peptides and proteins.

What is a polypeptide?

A polypeptide is a polymer with a definite sequence of amino acids held together by covalent peptide bonds.The peptide bond is the result of a condensation reaction between two amino acids: the carboxyl of one amino acid reacts with the amino of its neighbor, releasing a molecule of water (H2O).Short chains of amino acids connected by peptide bonds are called peptides.Peptides usually consist of as many as 20-30 amino acids.Amino acid residues with long chain connections of specific sequences are called polypeptides.Polypeptides can contain up to 4,000 residues.Polypeptides are characterized by a polypeptide skeleton composed of repeated atomic sequences at the core of the linked amino acid chain.The R group of the specific side chain of amino acid is connected with the main polypeptide chain.Peptides can be folded into fixed structures that form proteins.Thus, peptides form linear sequences of amino acid residues forming the primary structure of proteins.

What is protein?

Proteins are structurally and functionally complex molecules.The term protein is used to describe a three-dimensional structure formed by folding one or more polypeptides.Proteins show four levels of structural organization, with polypeptides as the main structure.Proteins have secondary structure when polypeptide chains are folded into alpha helix and beta.The tertiary structure of the protein constitutes the complete three-dimensional structure of the polypeptide chain.When more than one polypeptide chain is involved in a protein complex, the protein structure is designated as quaternary ammonium.Polypeptide chain folding to form proteins is based on the formation of many weak non-covalent bonds between different parts of a chain or even two or more polypeptide chains.Non-covalent bonds involve atoms of the main polypeptide chain and side chain R groups, and have three types: hydrogen bonds, ionic bonds and van der Waals bonds.A large number of weak noncovalent bonds operate in parallel and their strength binds to ensure the stability of the folded protein structure.The substructure of protein tissue is protein domain.It consists of any part of a polypeptide chain that can be independently folded into a stable structure.Each domain contains 40 to 350 amino acids.The smallest proteins present a single domain, while large proteins may contain as many as dozens of domains.Each domain of a protein is usually associated with a different function.The functional properties of proteins depend largely on their structure and shape, enabling them to interact with other molecular physics.These interactions are always specific and selective.Each protein can bind to one or more molecules called ligands with a high affinity to its ligand binding site.Ligand binding sites are cavities on the surface of proteins formed by folding polypeptide chains.Individual ligand-binding sites in proteins can bind to different ligands, regulate protein function, or help move proteins to specific sites in cells.Protein function is closely related to its structure.Changes in an amino acid can destroy its shape and result in loss of function.

Difference between polypeptide and protein

1, Definition of polypeptide and protein

A polypeptide is a polymer formed by a defined sequence of amino-acids linked together through covalent peptide bonds.

A  protein is a structurally and functionally complex molecule formed by the folding of one or many polypeptide chains.

2, Structural differences in polypeptide and protein

A polypeptide presents a simple structure and consists of the polypeptide backbone formed by the repeating sequence of atoms at the core of the linked amino-acids chain. Attached to the polypeptide backbone are the amino-acids specific side chains, the R group

A protein, on the other side, is a complex molecule consisting of one or more polypeptide chains folding into secondary, tertiary or quaternary structure.

The protein shape is held stable by three types of weak non covalent bonds: hydrogen bonds, ionic bonds, and van der Waal bonds.

3, Function of polypeptide and protein

The main function of a polypeptide is being the primary structure of more complex proteins. Polypeptides lack the three-dimensional structure which enables a protein to bind to a ligand and be functional.

On the other side, the structural complexity of a protein, its stable shape with its ligand-binding sites enables it to bind specifically and with high affinity to particular ligands, to be regulated, and to participate in many vital cellular metabolic pathways.

Summary of polypeptide vs. protein

Polypeptides and proteins are naturally occurring and essential organic compounds of a cell.

While amino-acids are their common primary component, polypeptides and proteins present major structural and functional differences:

1, A polypeptide is a simple polymer of amino-acids linked by covalent peptide bonds, while a protein is a complex molecule characterized by a stable structure composed by the folding of one or more polypeptide chains, held together by non covalent bonds.

2, A polypeptide’s main function is being the primary structure of a protein, while a protein is a complex compound, with ligand-binding sites enabling it to bind to specific and different molecules and be functionally active in the cell.

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