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Renin Angiotensin Mechanism.

Structure of Proteins

Structure of Proteins


Proteins:


Proteins are large biological molecules consisting of one or more chains of amino acids.


Amino Acids:


Amino acids are biologically important organic compounds made from amine (-NH2) and carboxylic acid (-COOH) functional groups, along with a side-chain specific to each amino acid.


Structure of Proteins:



  • A protein function depends upon on its specific conformation.

  • The primary structure of a protein is determined by the gene corresponding to the protein. In molecular biology, protein structure describes the various levels of organization of protein molecules, which includes:-


• Primary structure

  • Secondary structure

  • Tertiary structure

  • Quaternary structure


structure of proteins

Primary Structure



  • The primary structure of proteins is the unique sequence of amino acids.


 

Secondary Structure



  • The secondary structure of protein results from hydrogen bond at regular intervals along the polypeptide backbone.

  • The typical shapes that develop from the secondary structure are:-



  1. An Alpha Helix (Coil)

  2. Beta Pleated Sheet (Fold)


 

Tertiary Structure



  • Tertiary structure refers to a three-dimensional structure of a single protein molecule.

  • The tertiary structure of protein results from varieties of attraction between the R groups or between the R group and the polypeptide backbone.

  • The interactions includes



  1. Hydrogen Bonds (among polar areas)

  2. Ionic Bonds (among charged R – group)

  3. Hydrophobic interactions (among hydrophobic R-group)

  4. Van Der Waals Interactions (among hydrophobic R-group)

  5. Disulfide bridges (Strong covalent bond that forms between sulfhydryl groups (SH) of cysteine monomers, stabilize the structure)


 

Quaternary Structure



  • Quaternary structure results from the aggregation of two or more polypeptide subunits.

  • The quaternary structure is stabilized by the same non-covalent interactions and disulfide bonds as the tertiary structure.


Examples:


Hemoglobin 



  • The protein hemoglobin is made up (primarily) of 4 polypeptides.

  • Typically, when a protein is made up of multiple polypeptides, each polypeptide is simply called a protein subunit.

  • However, in the case of hemoglobin, the subunits are each called globin.

  • hemoglobin

  • The 4 globins are of two types.  2 of them with identical amino acid sequences (primary structure) are called alphaglobins (a-globins), while the other 2 also have identical amino acid sequences and are called beta-globins (b-globins).

  • Every hemoglobin molecule contains 2 a-globins and 2 b-globins.

  • Each of the globins is folded into a secondary and tertiary structure.

  • Then, all four are put together into the hemoglobin molecule's quaternary structure.


Insulin 



  • Insulin is composed of two peptide chains referred to as the A chain and B chain.

  • human insuline

  • A and B chains are linked together by two disulfide bonds, and an additional disulfide is formed within the A chain.

  • In most species, the A chain consists of 21 amino acids and the B chain of 30 amino acids.

  • It is a dimer of an A-chain and a B-chain, which are linked together by disulfide bonds.


Albumin


albumin

  • The general structure of albumin is characterized by several long α (alpha) helices, this allows it to maintain a relatively static shape, something essential for regulating blood pressure.

  • Serum albumin contains eleven distinct binding domains for hydrophobic compounds. One hemin and six long-chain fatty acids can bind to serum albumin at the same time.


Myoglobin (Does not Possess Quaternary Structure)



  • Myoglobin consists of a single protein chain with 153 amino acids and one heme group that stores oxygen in the muscle cells.

  • myoglobin

  • Myoglobin has a stronger affinity for oxygen than hemoglobin, which enables the oxygen to shift from one to the other.


 

Globulin 


globuline

  • It has helices and strands, 13 and 19 respectively.

  • The major beta-sheets of globulin are named the A-sheet and the B-sheet.

  • The 13 helices are each lettered beginning with letter A.

  • The molecule has five cysteine residues but has no disulfide bonds; so sulfur so is not responsible for holding together globulin structure.


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