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CARNIVAL OF CHEMISTRY: THE STRUCTURE OF PROTEIN CHEMISTRY

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Proteins can be defined as the realization of genetic information, it is only thanks to them whether the cells can function adequately, there are multiple types with different functions: enzymes involved in cellular reactions, proteins transport such as hemoglobin, etc. ... Protein is a miracle of engineering molecular stability of protein structures is crucial for their correct operation and to lord it in determining the correct three-dimensional conformation of the proteins involved must take specific chemical bonds in a particular hydrogen bonding, hydrophobic interactions, covalent bonds for example.

Bricks "molecular" with which a cell manufactures proteins are molecules known as amino acids, proteins are composed of specific sequences of amino acids, which determine the structure and specific functionality. Because a protein to function it needs to perform a specific riiegamento of / and peptide sequences that make? but mostly because a native conformation of a protein is preferred to another?

cellular environment, the amino acid sequence, chemical bonds between the aqueous environment and the same amino acid structure to make it all an intricate jigsaw puzzle where each molecule has a definite post to be filled to maintain the native conformation of a protein.

The base of protein structures: the peptide bond.

Because the amino acid sequences that form a protein can not take many shapes? The amino acids tend to bond with each other ... through the covalent bond is a type. The formation of covalent bonds between amino acid residues poses important constraints on conformations of a peptide. The structure that is to look at is as follows:

Cα - C - N - Cα . that is, each alpha carbon is separated by three covalent bonds arranged in the specific sequence. Many studies carried out by techniques of X-ray diffraction showed that the amide bond C - N in a peptide are shorter than those formed in an amine and fli asociar atoms to bond soo Sulo same plane. This indicates the presence of a resonance or a partial redistribution of pairs of electrons between the oxygen atom cabonilico and the amide nitrogen atom. The oxygen is in such a way you've bought a small partial negative charge, and nitrogen partial positive charge, creating an electric dipole possoclo. All this determines that the peptide bond is planar and the six atoms of the bond he peptide are prepared on the same level Doing that the oxygen atoms of the carbonyl group and amide nitrogen are in a position

trans addition amide are not able to rotate freely due to the redistribution of electrons just before you come to ccennata formed by the bond, which causes the presence of a partial double bond. then the rotation is limited only to the bonds N - Ca and Ca - C with the result that legmai cvalenti that are created between the various amino acids greatly reduced the number of conformazion that could be taken.

The secondary structure EFERENCE term secondary structure is the conformation of local parts of a polipepride. The discussion will focus Nosrati princialemente on some type of repetitive folding of a sheletro polipepride. The type of secondary structure stavili and universally distributed proteins are in fact relatively few. The most relevant conformations are the alpha helix and beta sheet folded. ...

alpha helix

The alpha helix is \u200b\u200bperhaps the simplest provision na polypeptide chain can assume, as you can see in the picture is a true helical structure, where the portion internal structure of atoms are involved in peptide bonds, while the exterior side chains of amino acids. Because this type of structure is better compared to other form?

The answer is because in this conformation the atoms carrying hydrogen bonds ... in fact, the alpha helix is \u200b\u200bstabilized by hydrogen bonds between the hydrogen atom bonded to nitrogen and electropositive of all bonds pepetidico atoo of the ossigenocarvonilico elettronegatico the fourth amino acid residue next amminoterminale Set in the amino acid chain. quindiogni peptide bond partecpa the maintenance of this structure through hydrogen bonds. The set of three or four hydrogen bonds per revolution of the propeller, mean that the structure is carefully resealed and kept stable. There is an important detail to add, it depends on the stability of alpha helix by hydrogen bonds formed between atoms of hydrogen and nitrogen of peptide bonds, but also depends on the amino acid sequence, in fact, not all peptides can form a stable alpha helix. Some amino acid residues may destabilize the secondary structure unlike the other. Take for example a polypeptide chain with many basic amino acid residues (containing many residues Arg or Lys or Glu, for example) can not be formed because the carboxyl groups of all positively charged side chains are preventing repingeranno the formation of alpha helix. Restrictions may also be due ale latarali size of chains, such as amino acid residues Asn, Ser, Thr, and Cys (... serine, threonine, cysteine) can cause instability if the alpha helix are very close ... Instability is also a result of chance of amino acid residues proline (Pro) and glycine (Gly). Proline as you can see in the picture consists of a rigid ring, the nitrogen atom is part of the ring and can not be any rotation around the CN bond of the peptide bond, which determines that each proline residue introduces a retreat in destbilizzante an alpha helix structure. In addition, the nitrogen atom of a proline residue involved in a peptide bond, the atom has no ifrogeno sostituiente is necessatuio Fenera for a hydrogen bond with other residues motii For these offspring and only rarely present in na 'alpha helix. Glycine instead for various reasons can confer instability. Unlike the proline ... Other reasons may cause instability of alpha helix, esmepio to the type of amino acid end of the segment involved in this particular qusto folding. In each peptide bond exists poccolo dopolo Electric, the sum of the dipoles through the hydrogen bonds inside the helix dipole and the net increase with the length of the propeller. Typically the last three or four reisdui amino acid tend not to participate in the formation of these bonds, eg give some support through their positive or negative. In fact, the positive or negative charges on the helix dipoles residing on the C = O and NH groups of peptide bonds to the carboxyl and amino terminal ends, because another feature of the helices is that the positively charged amino acids tend to carboxy end is found terminal and the negative end amminoterminale ... So there are five restrictions possoo marshmallow structure of alpha helix:

electrostatic repulsion between amino acid residues with charged R groups

The size of the amino acid chains positively or negatively charged side

interaction between amino acid residues spaced three or four remaining

the presence of Pro and Gly residues of the interactions between amino acids fli all'estrmitàò prop, and generated dopolo from this structure.

The beta sheet fold.

A second reason is highly repeated in the protein known as beta conformation. In the beta conformation of the polypeptide chain covalent skeleton is extended to zigzag like a real piece of paper folded. The polypeptide chains are subject of a side by side. In general, the R chains of amino acid residues protruding outside the structure, forming a zig zag in this way a staggered sequence. Again there may be restrictions on the sequences that can form these structures. When two layers are very close in a protein structure of the chain R groups must be relatively small in order to avoid any steric hindrance.

be noted in particular the folding beta, a withdrawal of 180 ° which consists of four amino acid residues with the carbonyl group of the first amino acid that forms a hydrogen LM with the amino group of the fourth residue, the central peptide groups do not participate the link. Ripegamenti are often present in these amino acids such as Gly and Pro, the first as small and flexible, the second because it lends itself very well to induce folding because of its structure.

Tertiary structure
• For tertiary structure refers to the final folding of the protein, while Specimen layout secondary folds are sub-regions that are associated with the amino acid sequence, tertiary structure in the various secondary structures, and then residual in sub-structural amino acid that were far apart in the sequence are close together.
• Some proteins contain multiple polypeptide chains that can secodna cases to also be identical or different. the union of these polypeptide chains is to determine a particular type of folding defined quaternary structure. The proteins can be divided into two types, fibrous and globular. The two groups are distinct structurally and functionally anhée, the former are mainly involved in the formation of structures that determine the shape of the resistance of the cells of vertebrates, while the enzymes and proteins with transport functions, for example, have essentially a globular structure.