Dhristi JEE 2022-24

What is Polypeptide?

The answer to the question, what is polypeptide, is an easy one. A polypeptide helps make proteins by bonding several amino acids together. When two or more polypeptides bond, then proteins are formed. These are then folded into particular shapes to form a specific protein. The functions of polypeptides are structural support, hormones, enzymes, and transporters. Some polypeptide examples are discussed below.

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What is Polypeptide Chain?

Proteins happen to be complex polymers, and they comprise hydrogen, carbon, oxygen, and nitrogen. They are huge macromolecules that are created from amino acid monomers. An amino acid is a molecule that has a carboxyl group or COOH besides an amino group or -NH2. The side chain or R group that is linked to the carbon atom happens to be the identifier that conveys the distinguishing factors between amino acids.

A few R groups are non-polar, whereas some are polar. Again, some are tiny, while some are massive ring structures. More than twenty R groups are present, and so, there are more than twenty kinds of amino acids. They are joined together by some peptide bonds for forming polypeptides. To understand the polypeptide chain of amino acids, it is important to know that peptide bonds happen between a group of amino acids and carboxyl, and so, the R group doesn’t affect the formation of the bond. It means any amino acid is capable of forming peptide bonds with other amino acids. This arrangement of amino acids that happens in a polypeptide gets dictated by DNA.

Four Levels of Protein Structure

For understanding proteins well, you need to observe the four levels of protein structure, and they are:

  • The primary structure of a protein is its arrangement of amino acids.

  • When it is the secondary structure, then it is the shape of the peptide chain.

  • When a protein possesses several polypeptide chains, then the manner in which they are sequenced is called the quaternary structure.

The tertiary structure is considered the 3-dimensional structure of a polypeptide chain. Proteins happen to be vital in contracting muscles, the immune system, and transporting oxygen. A few proteins do regulate cell processes, whereas some control the reaction rate. A polypeptide bonds many amino acids together for creating proteins, and it also gives them their exclusive shape. 

What are Amino Acids?

Polypeptides and their specific amino acid groups have similarities in structure, but they are linked by electron-sharing bonds or covalent bonds. An amino acid is the fundamental building block of a polypeptide. There are twenty distinct amino acids, and all have particular structures. When you understand the amino acids’ structure, you can get the notion of the method in which they would bond together with various other amino acids.

The Classes of Peptides

People know various types of peptides, and they are categorized or classified based on their functions and sources. A group of peptides comprises bacterial or antibiotic peptides, plant peptides, invertebrate peptides, fungal peptides, venom peptides, skin or amphibian peptides, anticancer or cancer peptides, inflammatory peptides, vaccine peptides, ingestive peptides, endocrine peptides, cardiovascular peptides, gastrointestinal peptides, opiate peptides, respiratory peptides, blood-brain peptides, and neurotrophic peptides.

A few ribosomal peptides remain subject to proteolysis, and these function as hormones as well as signaling molecules. A few organisms create peptides in the form of antibiotics, like bacteriocins and microcins. Most frequently, peptides have post-translational modifications, like hydroxylation, phosphorylation, palmitoylation, sulfonation, disulfide formation, and glycosylation. 

Generally, peptides tend to be linear though lariat structures are observed. Again, more exotic manipulations too happen. Enzymes assemble some non-ribosomal peptides instead of the ribosome. A usual non-ribosomal peptide is called glutathione. This is an element of the antioxidant defenses of the majority of aerobic organisms. Some other non-ribosomal peptides tend to be common in plants, fungi, and unicellular organisms.

Polypeptides are considered biomaterials that comprise repeating units of amino acids, and they are connected by a specific polypeptide bond. A polypeptide is capable of conforming to various 3-D architectures based on its chemical composition. This kind of versatility, coupled with some inherent biological activity and biocompatibility, makes the polypeptide group ideal for gene transfer applications besides the growth of tissue scaffolds.

FAQs on Polypeptide

1.What are proteins, and how are they important?

Proteins are hugely vital for the functioning of the cells. The word “protein” has been derived from “proteios,” which is a Greek word, and it means first place. Proteins help support structures present in the cell and with the storage and transport of substances. Again, proteins also work for defending the cell besides controlling metabolic functions. Proteins happen to be hugely complex and diverse, and every kind of protein does hold its particular shape. When the pH or temperature of the environment of a protein is changed or when it remains exposed to chemicals, then some interactions get disrupted. This helps the protein in losing its 3D structure.

2.What is the polypeptide structure?

A polymer gets created by living organisms known as a biopolymer. Commonly, there are four significant categories of biopolymers, and they are:

  • Polypeptides

  • Polysaccharides

  • Fatty acids

  • Polynucleotides

Polypeptides are considered unbranched chains comprising amino acids, and they remain connected together through peptide bonds. A peptide bond does the job of linking the carboxyl group of amino acids with the amino group of another amino acid for forming an amide. A short polypeptide is named according to the monomeric amino acids. For example, a dipeptide happens to be a peptide that comprises a couple of amino acid sub-units, whereas tripeptides are peptides that comprise three amino acid subunits.

3.How are polypeptides formed?

The variation that is present in the R-group side chains changes the chemistry of an amino acid molecule. The majority of the amino acids possess side chains, and they are non-polar, which means they don’t have negative and positive poles. Some have negatively or positively charged side chains, whereas some possess polar side chains, and they remain unchanged. When the amino acids have charged side chains, then they form ionic bonds, and when the side chains tend to be hydrophobic, then they can be linked with van der Waals interactions. A polar amino acid can link with hydrogen bonds, and so side-chain interactions of long chains of amino acids besides their arrangement do determine the method in which a protein molecule will be formed.