In organic chemistry, a peptide bond is an amide type of a covalent chemical bond that combines two consecutive alpha-amino acids of C1 (carbon number one) of one alpha-amino acid and N2 (nitrogen number two) of another along a peptide or protein chain.  Theoretically, the free rotation around these links allows angles of -180 to 180 degrees. In reality, steric and energetic factors limit the possible combinations. These binding angles play a key role in determining the secondary structure of proteins. For example, the values of Φ and Ψ in α propellers are about −60 and −45 degrees respectively. The secondary structure will be discussed in more detail later in this chapter. The absorption wavelength of a peptide bond is 190–230 nm (making it particularly sensitive to UV rays). The so-called isopeptide bonds refer to the amide bonds between the amines of the side chain or the carbonyl carbons on the side chain and not to the α-amine or the α-carbonyl. In glutathione, for example, the γ-carboxyl group of glutamic acid is related to the α amino group of cysteine. During translation, peptide bonds are formed from amino (N) to the carboxyl terminus (C) by removing water (also called dehydration or condensation) and catalyzed by RNA (called ribozyme), which is part of the ribosome.37 Peptides are also synthesized in vitro for therapeutic and experimental purposes. Such chemical peptide synthesis proceeds from C to N-terminus using N-protected amino acids and catalyzed by N,N`-dicylohexylcarbodiimide.38,39 In this scheme, the nucleophilic amine group reacts with a carbodiimide: carbonyl intermediate, which leads to the formation of a new peptide bond and a dicyclohexylurea. Dicyclohexylurea is insoluble in most solvents and can be easily removed from the maturing peptide.
The cleavage of peptide bonds can be obtained non-specifically by acid hydrolysis or specifically by a variety of proteolytic enzymes having affinity for bonds between specific amino acid residues. These protease systems are described later in this chapter. Selection of the specific aminoacyl tRNA to bind to ribosomal site A is done by base matching between the relevant mRNA codon and tRNA anticodone. Since this interaction comprises only one base triplet and therefore a maximum of nine hydrogen bonds (see Fig. 1B), it is inherently unstable at physiological temperatures and is probably stabilized by ribosome components to allow sufficient time for the synthesis of peptide bonds. In addition, the codon-anticodon pairing should be monitored for accuracy to minimize translation errors. In E. Coli, there is genetic and biochemical evidence that one of the proteins of the small ribosomal subunit, S12, is involved in the accuracy of normal translation and causes the mistranslation that occurs in the presence of the antibiotic streptomycin due to incorrect codon-anticodon interactions.
The four-atom function group -C(=O)NH- is called an amide group or (in relation to proteins) a peptide group. Long-chain polypeptides can be formed by combining many amino acids via peptide bonds. The amide bond can only be broken by amide hydrolysis, in which the bonds are divided by adding a water molecule. Protein peptide bonds are metastable and break spontaneously in a slow process. Living organisms have enzymes that are capable of both forming and breaking peptide bonds. In living organisms, the process is usually catalyzed by enzymes known as peptidases or proteases, although there are reports of hydrolysis of peptide bond caused by a conformation strain when the peptide/protein folds into the native structure.  This non-enzymatic process is therefore accelerated not by the stabilization of the transitional state, but by the destabilization of the ground state. In a highly alkaline solution, all compounds containing two or more peptide bonds react with copper salts to form a purple color. This reaction is used as the basis for a qualitative test for proteins; When quantified, it provides a useful colorimetric measurement of proteins. In the case of helical peptide layers, which have a positive surface potential, the situation is significantly different from peptide layers, which have a negative surface potential. The surface potentials of the BA16Lipo SAM and the UL16T and BL16T multilayers were between 400 and 600 mV. These three types of helical peptide layers differ in the thickness of the layer; a single layer for BA16Lipo, about five layers for UL16T and about 10 layers for BL16T.
Therefore, the surface potentials of these helical peptide layers can be saturated and independent of the thickness of the layer. This observation can be explained by the charge exchange mechanism at the gold-polypeptide interface, since the dipole moment of the propellers favors the transfer of the electric charge from the gold to the polypeptide layer at the interface . The positive surface potential must be generated under thermodynamic equilibrium at the interface. A peptide is a molecule composed of two or more amino acids. The bond that holds the two amino acids together is a peptide bond or covalent chemical bond between two compounds (in this case, two amino acids). It occurs when the carboxylic acid group of one molecule reacts with the amino group of the other molecule, connecting the two molecules and releasing a molecule of water. The ribosome is a very large and complex cellular structure composed of proteins, RNA and various other components that help in the catalysis of the formation of a peptide bond. This is called the stretching step of protein synthesis. The ribosome helps to match the tRNA with the corresponding mRNA.
In turn, RNA changes shape slightly, which catalyzes the reaction between two amino acids and ejects a molecule from water. The chain that forms leaves the ribosome. The ribosome, which is itself a large protein, changes shape after the reaction has taken place and moves lower into the mRNA strand, causing the process to start again. Finally, a codon that signals the end of the protein is encountered and the ribosome is informed that the entire protein has been created. At this point, the mRNA and the new protein are expelled and a new mRNA is absorbed, creating a completely different protein. It can also be called eupeptide bond to separate it from an isopeptide bond, another type of amide bond between two amino acids. Serine endoproteases with a serine residue at their active sites involved in the catalytic reaction have broad specificities, and in fact these enzymes catalyze hydrolytic reactions with esters and amides, as well as peptides. Important known enzymes in this subgroup are chymotrypsins and subtilisins. Many serine proteases have a high optimal pH in the range of 7-12, with those in the pH range 9-10 known as alkaline serine proteases or the first generation of detergent proteases and those with a pH optima of 11-12 as highly alkaline proteases, the second generation of detergent proteases.
Subtilisins are an important family of serine proteases produced by Bacillus species. These enzymes were also the starting material for the development of a third generation of detergent enzymes resistant to oxidation by bleach and oxidants of related detergents, in which an oxidation-sensitive amino acid near the active center of the enzyme was replaced by an oxidation-resistant amino acid. These enzymes are discussed below under the commercial proteases of Bacillus. The division of electrons in the amide bond (also known as the ω bond) is delocalized and effectively prevents rotation around this bond. This binding is fixed in a layer. The conformational flexibility of the peptide backbone results entirely from the rotation around the axes of the two carbon bonds α. The angles of rotation around these bonds are called Ramachandran angles.40 The nitrogen-α-carbon bond angle is called the Φ angle, and the α-carbon-carbon bond is called the Ψ (bottom) angle. A peptide bond is a covalent bond formed between two amino acids.
Living organisms use peptide bonds to form long chains of amino acids called proteins. Proteins are used in many roles, including structural support, catalysis of important reactions, and detection of molecules in the environment. A peptide bond is therefore the basis of most biological reactions. The formation of peptide bonds is a prerequisite for all life, and the process is very similar in all forms of life. A peptide bond is a chemical bond formed between two molecules when the carboxyl group of one molecule reacts with the amino group of the other molecule, releasing a water molecule (H2O). The formation of peptide bonding consumes energy, which is derived from ATP in organisms.  Peptides and proteins are chains of amino acids held together by peptide bonds (and sometimes by certain isopeptide bonds). Organisms use enzymes to produce non-ribosomal peptides and ribosomes to produce proteins through reactions that differ in detail from dehydration synthesis.  Some peptides, such as alpha-amanitin, are called ribosomal peptides because they are produced by ribosomes, but many are non-ribosomal peptides because they are synthesized by specialized enzymes rather than ribosomes. For example, glutathione tripeptide is synthesized in two stages from free amino acids, by two enzymes: glutamate-cysteine ligase (forms an isopeptide bond that is not a peptide bond) and glutathione synthetase (forms a peptide bond).   The carbon-nitrogen bond formed in a peptide bond is different from the carbon-nitrogen bonds in other parts of the molecule. The oxygen on the carboxyl side of the bond is slightly negative in charge.