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Levels of protein structure.

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Levels of Protein Structure Proteins are a group of organic compounds whose molecules consist of carbon, oxygen, nitrogen and sometimes sulphur atoms. They are condensation polymers of amino acids. Each amino acid carries two functional groups ( an amino group - NH and a carboxyl group - COOH.) These two functional groups are attached to a alpha-carbon along with hydrogen and the 'R' group. The 'R' group differs from amino acid to amino acid. Amino acids can be joined together by condensation. A hydrogen atom is removed from the amino group of one amino acid and this combines with an - OH group removed from the carboxylic acid of the other, forming a molecule of water. This is called a dipeptide bond. ...read more.


or to fold into sheets (beta pleated sheet). The secondary structure of proteins occurs due to the formation of hydrogen bond in the polypeptide. It is the hydrogen bond which keeps the particular shape of the polypeptide chain. These hydrogen bonds are present in the backbone of every polypeptide. The backbone of every polypeptide is exactly the same and therefore many polypeptides can take up same shapes. In alpha-helix, hydrogen bonds are formed between the CO of one amino acid with the NH of and amino acid four further along the chain. This twists the chain into a spiral form which is maintained by the hydrogen bonds. There are 3.6 amino acids in 1 complete turn. The beta-sheets occurs as a flat zig-zag chain. ...read more.


These bonds are easily broken but very numerous. Ionic bonds form between amino and carboxyl parts present on some R-groups. They are stronger than hydrogen bonds. The ionic and hydrogen bonds are affected by changes in pH. The disulphide bond is a covalent bond which is formed between the R-groups of the amino acids such as cysteine which have -SH groups. This is the strongest bond of the 3. All these bonds and interactions cause proteins to have an irregular compact globular shape. The shape is also affected by the presence of hydrophobic R-groups. Some proteins are made up from more than 1 polypeptide chain. This is also known as the quaternary structure. An example is haemoglobin which consists of 4 separate polypeptide chains. This structure can be used to describe the structure of conjugated proteins. These proteins contain amino acid and some other chemical molecule. Finally they are specific in globular proteins. ...read more.

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