Peptides are chains of amino acids that form proteins. Amino acids have amino and carboxylic acid groups, and their structure affects the properties of peptides. Peptide synthesis occurs when amino and carboxylic acid groups bond to form amide groups. Proteins have different levels of structure, including primary, secondary, and tertiary. The tertiary structure determines the protein’s biochemical properties, which can be used in pharmaceutical product design.
Peptides are biological polymers formed by the bonding of amino acids, the key elements of which are carbon (C), hydrogen (H), oxygen (O) and nitrogen (N). The term “peptide sequence” refers to the order in which amino acids are linked. Peptides are very important in living systems and combine to form much larger chains called proteins. While there are many varieties of biological peptides, most of them consist of only 20 amino acids. Proteins perform a number of biological functions, including those as enzymes and in the structure of plant cell walls and membranes in animal cells.
Amino acids are so called because they have amino groups (-NH2) and carboxylic acids (-CO2H). Most of the amino acids found in biological systems have the general formula R-CH(NH2)-CO2H, where R is a range of groups. The variable structure of R is what affects the structure and properties of peptides and proteins.
Peptide synthesis occurs when the amino group of one amino acid reacts with the carboxylic acid group of another amino acid. The result is the formation of an amide group of the structure -N(H)-CO- where the nitrogen-carbon bond is called a peptide bond. The reaction can occur any number of times to form a peptide sequence of several functional groups, each of which is interspersed with an amide group.
Peptides and proteins have different levels of structure. The structure of the primary protein is the order in which the amino acids are found; this is its peptide sequence. The functional groups on the protein interact with each other to give it a shape. The individual twists of a peptide are called its secondary structure. Its overall shape, the net result of all these twists and turns, is the tertiary structure of the peptide.
The biochemical properties of proteins or peptides depend on the tertiary structure. As with all chemicals, protein will take the most energetically favorable form. This shape is due to the attractive and repulsive forces between groups on individual amino acids. Thus, the tertiary structure is due to the primary structure, which means that deducing the peptide sequence of a particular protein will ultimately explain its properties.
Processing the peptide sequence of a protein has applications in pharmaceutical product design. Many biological processes depend on the actions of proteins, and drugs often work by copying or blocking the action of these proteins. Understanding the behavior of proteins could lead to the design of more effective drugs. For this reason, a pharmaceutical company’s R&D department typically has a peptide library or peptide catalog that it will use in researching new drugs.
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