Amino Acids and Peptides

A single amino acid unit is a dipeptide; chains of three or more are tripeptides. The peptides are isolated from protein sources by hydrolysis or microbial fermentation, and then identified and confirmed for bioactivity.

Their use has been delayed by the challenges of scalable production methods, oral absorption, gastro-intestinal stability and lack of well-designed clinical trials to support health claims.

Amino Acids

Amino acids are the building blocks of peptides and proteins. They are organic compounds that join together by forming a covalent bond between the amino group (-NH2) of one amino acid and the carboxyl group (-COOH) of another amino acid. Amino acids may be genetically encoded or synthesized in the laboratory, and they are found naturally in both plants and animals.

The sequence and spatial structure of the amino acid side chains determine how a peptide folds into its three-dimensional shape to perform its biological function. A peptide chain containing two or more amino acid residues is called an oligopeptide; when the chain has 20 or more amino acid residues, it is referred to as a polypeptide.

Amino acid side chains can be basic, like lysine, or acidic, such as glutamic acid. Moreover, some of them can form hydrogen bonds with other amino acids in the peptide chain or with water molecules, which contribute to the stability of the peptide structure and the formation of a cyclic structure that is required for the functional activities of peptides.

Although the primary structure of a peptide can be assembled in the lab by joining amino acid residues, chemists cannot assemble the secondary, tertiary and quaternary structures that are established in living organisms, because these higher-order structural features depend on the dynamic interactions of many factors, including pH, temperature and inorganic ion concentration. These factors affect the conformational coiling of the peptides and their tertiary structures, which then influence their functions.

As a result, the bioactive effects of peptides are primarily the result of the specific amino acid side chains that constitute the peptides’ primary structure and not their three-dimensional structure. Consequently, the only bioactive peptides currently approved for human use are synthetic short peptides (2-10 amino acids) such as anidulafungin and palmitoyl tetrapeptide-7. However, the ability to extract naturally occurring bioactive peptides from foods such as chicken and eggshells may become an important new method for producing therapeutic peptides.

Natural peptides may be extracted from food products using the methods of enzymatic hydrolysis and fermentation, or by chemical synthesis. The latter method involves the chemical synthesis of amino acids and other building blocks, which are then joined together by a peptide bond to form the desired peptide. The peptides are then subjected to purification steps to ensure their quality and safety for use as human health supplements.

Peptide Bonds

The peptide bond is the covalent chemical bond that connects two amino acids together. It forms when the carboxyl end of one amino acid reacts with the amine end of the next amino acid and eliminates a water molecule during the process. Two amino acids connected by peptide bonds form a polypeptide chain. There are 20100 possible combinations of monomers (amino acid chains) that can be joined together to form a polypeptide. Polypeptides are the basic building blocks of proteins.

The polypeptide chain has different functions depending on its length and composition. It can be folded into a three-dimensional structure, known as secondary structure, or it can be arranged in a flat sheet called tertiary structure. It can also have a network-like structure, known as quaternary structure.

Proteins have many different functions in living organisms. They perform tasks such as transporting, binding, catalyzing, and regulating processes. Proteins are naturally occurring polymers, and there is a wide variety of proteins in different organisms. There are even different types of proteins in a single organism. The number of amino acids in a protein depends on its function and on the organism’s needs.

There are four groups that make up an amino acid: a carbon atom with two hydrogen atoms, a carboxyl group and an amine group. The amine group has a nitrogen atom attached to it. The carboxyl group has a carbonyl oxygen attached to it. The peptide bond is formed when the carboxyl oxygen from one amino acid reacts with the amine nitrogen from another amino acid. This reaction is called a condensation reaction. The resulting peptide bond is called the amide bond.

The peptide bond has the same properties as a double bond, except that it cannot rotate like a single bond can. Because of this, the peptide backbone has a limited amount of flexibility. In addition, the peptide bond is usually found in cis configuration, meaning that the carbonyl oxygen and the amino hydrogen face each other.

When a peptide chain has a free amino group on one end, it is considered the N-terminus and the other end with a carboxylic acid has the C-terminus. In peptides and proteins, the N-terminus is usually indicated first. By convention, peptides and proteins are written with the N-terminus on the left side of the molecule.

Peptide Structure

The carboxyl group of one amino acid reacts with the amide nitrogen of another to form a covalent bond. These bonds link together the amino acids to form a linear molecule known as a polypeptide. The number of amino acids in a polypeptide determines its length and can be described by the term dipeptide (two amino acid residues) or oligopeptide (relatively few amino acid residues). A polypeptide can also be composed of several dipeptides connected by peptide bonds.

The peptide bond is slightly shorter than a standard single bond, due to the partial delocalization of pi electrons from the carbonyl carbon into orbitals shared by the amide nitrogen. This feature prevents rotation of the bond and limits the allowed values of three dihedral angles, Phi, Psi and Omega. The peptide bond has a cis conformation (chains are parallel to each other) and a trans conformation (chains are perpendicular to each other). The cis conformation is strongly favored over the trans conformation by steric interference between consecutive amino acid side chains.

Because of the structure of the peptide bond and its side chains, a polypeptide chain is able to fold into two types of structures known as alpha helices and beta sheets. The regularity of these structures is a result of forces acting on the polypeptide chain, which can be attributed to hydrogen bonding, ionic interactions between acidic and basic R groups, and van der Waals interactions.

As a result of these interactions, the hydrophobic R groups in nonpolar amino acids tend to lie in the interior of proteins and the more hydrophilic R groups on polar amino acids face outside. This creates a protein’s complex three-dimensional tertiary structure, which combines the primary structure, secondary structure and quaternary structure to produce its specific function.

The unique sequence of amino acid residues in a protein is determined by its gene, which provides the code for constructing that particular protein. This sequence is translated into an RNA transcript, which is then converted to the correct amino acid sequence during protein synthesis. The peptides that are formed during this process then join to form the protein’s primary, secondary and quaternary structures.

Peptide Function

Peptides are small molecules consisting of amino acid monomers connected by amide bonds. They are the building blocks of proteins and are important in many biological functions of living beings. In general, peptides are considered to be more bioactive than proteins because they have smaller molecular weights and shorter structures. In addition, peptides can be produced in large amounts using chemical methods while protein production requires a cell to produce the amino acids needed for the synthesis of protein chains.

Peptide function is an essential part of human and animal biology, ranging from immune system functioning to the control of appetite and body weight. Peptides are also used in the production of pharmaceuticals and cosmetics. In fact, peptides have been responsible for some of the most effective antibiotics in recent history.

The most famous peptide is insulin, the hormone that regulates blood glucose and is essential for life. Insulin is synthesized in the beta-pancreatic cells of the pancreas from a precursor molecule called proinsulin. Proinsulin is then cleaved by proteases into its A and B chains. The A chain is secreted into the bloodstream and the B chain is excreted into urine. C-peptide (also called connecting peptide, and with molecular formula C112H179N35O46) is the 31 amino acid link between the A and B chains of insulin. It is measured in the urine and represents approximately 5% of the endogenous insulin secretion by the pancreas.

C-peptide interacts with a receptor coupled to the G protein, which causes multiple effects at the cellular level. It increases the quality of red cells and improves oxygenation of tissues; it increases blood flow in skeletal muscles, skin and kidneys; decreases glomerular hyper-filtering and albumin urinary excretion; and enhances the structure and function of nerves. Deficiency of this peptide is associated with the development of chronic complications of diabetes mellitus such as neuropathy and nephropathy.

Another peptide that has been of interest in recent years is peptide YY (PNX), which is highly similar to insulin. Its deficiency is associated with obesity and impairs adipose tissue metabolism. PNX is believed to be important in brown adipose tissue metabolism and stimulates the activity of adipose-specific protein X, whose activation is accompanied by a fatty acid breakdown in the liver.

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