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Protein: a detailed discription

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Biology Proteins Section A The primary structure of a protein is the sequence of the amino acids it contains, in the formation of a chain. This chain is held together by peptide bonds creating a polypeptide chain made up of hundreds of amino acids. These peptide bonds are formed from condensation reactions. When the amino group and carboxyl group join, water is then produced as a bi-product. The sequence of amino acids inside I cell is determined by the DNA in the chromosomes of the nucleus. It is so specific that changing just one amino acid could alter its function entirely. An example of a polypeptide chain would be: NH2 - Valine - Cysteine - Arginine - Glutamine - Leucine - Serine - COOH. The secondary structure of a protein is made when the polypeptide chain configures itself into a particular shape. ...read more.


These opposite charges attract to form the bonds. Ionic - these bonds occur between any charged groups that are not joined by a peptide bond. This type of bonding is stronger than the hydrogen but can be broken by temperature of a change in pH levels. Disulphide - Some amino acids like methionine and cysteine contain sulphur within them, and this is where the disulphide bonds occur. Disulphide bonds are exceptionally strong and they contribute to most of the structural strength of the protein. Hydrophobic effect - this helps only some proteins maintain their structure by when globular proteins are placed in a solution, their hydrophobic groups point inwards away from the water. Tertiary proteins can also be split into two categories: Globular and Fibrous Proteins. ...read more.


This diagram below provides an example of a quaternary structure. Section B A Haemoglobin molecule consists of four polypeptide chains. These chains are two identical alpha-glucose chains and two beta-glucose chains, all held together by a series of disulphide bonds. Within each chain there is an iron-containing group called Haem which allows it to pick up 4 oxygen molecules (one for each Haem group). The haemoglobin molecule is an example of a prosthetic group, which when joined to another protein creates a conjugated protein. Collagen is a Fibrous tertiary structure which contains three polypeptide chains. Each chain is coiled to form a helix and is then coiled round one another to form a rope like structure (as shown below). This structure is reasonably tough considering it is held together by hydrogen bonds. Collagen is a component of the blood, tendons and bones. ...read more.

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