Ø These -C=O and NH 2 groups occur along the length of the polypeptide chain in regular sequence. Ø Consequently, the slightly positive H is then attracted towards the neighboring electronegative oxygen of -C=O or nitrogen atom of -NH2 group. Ø Thus hydrogen attached to these high electronegative atoms will get a partial positive charge called δ positive whereas the electronegative atoms will get a partial negative charge called δ negative. Ø Due to the high electronegativity, Oxygen and Nitrogen attract the shared electron of hydrogen more towards them. Ø This is due to the high electronegativity of O and N when compared to hydrogen. Ø Hydrogen present in the –OH group or –NH 2 of amino acids become slightly electropositive. Learn more: How hydrogen bond is formed in Water? Ø Hydrogen bond definition: Hydrogen bond is an electrostatic attraction between a hydrogen atom, which is covalently bound to a high electronegative atom (such as Oxygen and Nitrogen), to another electronegative atom of same or different molecules of their close vicinity. Ø Disulfide bonds stabilize the tertiary structures of the protein. Ø A disulfide bond may be formed between the cysteine residues of same polypeptide chain or different polypeptide chain of a functional protein.
Ø They are very strong bonds and are not easy to break. Ø Disulfide bond in protein chemistry is better known as the disulfide bridge or S-S bond. Ø This reaction results in the formation of a permanent covalent connection between two cysteine residues called disulfide bond. Ø If two molecules of a cysteine line up alongside each other, the neighboring sulfhydryl groups can be oxidized. Ø The sulfhydryl is highly polar and highly reactive. Ø The cysteine (Cys or C, a sulfur containing amino acid) contain a highly reactive sulfhydryl group (-SH) in its side chain (R group). Ø Disulfide bond: a covalent bond formed from two thiol groups of two cysteine residues in a protein. Ø Tertiary and quaternary structures of proteins are stabilized by ionic bonds. Ø This is the reason for the denaturation of proteins in the acidic or basic medium. Ø Even a change in the pH may breakdown the ionic bonds.
Ø Ionic bonds are weak bonds and they are very fragile in an aqueous medium. Ø The attraction of oppositely charged R groups results in the formation of ionic bonds. Ø After the ionization of side chain as mentioned above, the amino acids in the protein chain can attract or repel each other based on their charges. Ø Basic R groups will be positively charged since they accept the H + ions from the medium. Ø Acidic R groups will be negatively charged since they release the H + ions. Ø These R groups can ionize to produce charged groups at certain pH. Ø The R groups (side chain) of certain amino acids contain additional acidic (-COO –) or basic (-NH 3 +) groups. Ø In proteins, the ionic bonds are formed between the ionized acidic or basic groups of amino acids. Ø Ionic bond definition: a chemical bond formed between two ions of opposite charges. Ø The primary structure of the protein is stabilized by peptide bonds. Ø In prokaryotes the 23S rRNA and in eukaryotes the 28S rRNA acts as the Peptidyl transferase enzyme. Ø Peptidyl transferase enzyme is a ribozyme it is a part of the ribosomal RNA (rRNA) of large subunit of ribosome. Ø Peptide bond formation is facilitated by the enzyme Peptidyl transferase during the translation process of protein synthesis.
Ø Many amino acids join together in this manner to form a polypeptide.
SHEPPARDSOFTWARE ION BONDING FREE
Ø The free amino group or carboxyl group of a dipeptide can form another peptide bond with a third amino acid and so on. Ø A dipeptide has a free amino group at one end and a carboxylic group at the other end. Ø The resulting compound after the peptide bond formation is called a dipeptide. Ø One molecule of water is eliminated during the formation of peptide bond by the condensation reaction of two amino acids. Ø Peptide bond formation is an example for a condensation or elimination reaction. Ø The peptide bond is represented as follows: Ø The carboxylic group (- COOH) of one amino acid combine with the amino group (-NH 2) of another amino acid to form the peptide bond. Ø It is formed by the joining of two amino acid residues during protein synthesis. Ø Peptide bond is a strong covalent bond with high bond dissociation energy.
0 kommentar(er)
