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1. Protein structure and function.pdf

5 Pages

Biology (Sci)
Course Code
BIOL 200
Richard Roy

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Naveen Sooknanan McGill Fall 2011 Protein structure and function: DNA is responsible for the transmission of information through transcription and translation in order to form RNA, and eventually, proteins. Proteins are an important part of the body as they perform a variety of functions depending on their shape.  Structural proteins determine the shape of a cell o The provide the structural rigidity of the cell o They also guide intracellular movements of various molecules and organelles  Enzymes are catalytic proteins which catalyze (speed up) various intercellular and intracellular reactions o RNA with 3D structure can also have enzymatic properties  Membrane transport proteins permit the flow of ions small organic molecules through the plasma membrane o i.e. oxygen, carbon dioxide, nutrients and waste  Regulatory proteins act as sensors which can control the activities of a cell o They can do this by regulating the function of other proteins, such as enzymes  Signalling proteins such as hormones or cell-surface receptors can transmit intracellular signals to the cell exterior  Scaffolding proteins bring other proteins together in order to increase functionality  Motor proteins are responsible for moving cells, organelles and consequently, the organism as a whole o They are molecular machines All of these proteins have 3 generalized functions:  Binding (motor proteins)  Catalyzing (enzymes)  Folding (plasma membrane) The shape of a protein is very important  It is the unique 3D structure of a protein which determines its function  An alteration in shape caused by a mutation can result in the loss of function or altered function of the protein A protein is built from monomers called amino acids. Their structure is made up of an alpha (α) carbon, a carbonyl group, an amino group, a hydrogen, and a varying group called an R group, all attached to the carbon in the following way:  On each amino acid, there is an amino terminus and a carboxyl terminus  The amino group of one amino acid can form a covalent bond with the carboxyl group of another amino acid. This bond is called a peptide bond.  There are 20 different R groups creating 20 different amino acids There are 2 possible isomers for an amino acid: D and L isomers, which are enantiomeric  L isomers make up almost all naturally occurring amino acids 1HYDROPHILIC AMINO ACIDS Basic amino acids SPECIAL AMINO ACIDS COO COO COO *H3N-C-H H3N-C-H CH H2C CH SH Proline Cysteine Glycine (Cys or C) Gly or G) (Pro or P) HYDROPHILIC AMINO ACIDS Basic amino acids SPECIAL AMINO ACIDS COO COO COO *H3N-C-H H3N-C-H CH H2C CH SH Proline Cysteine Glycine (Cys or C) Gly or G) (Pro or P)Naveen Sooknanan McGill Fall 2011  D isomers are rarely found naturally in living organisms although mutations can occur causing them to become more and more common  D isomers are useful for creating drug resistant bacteria because very few organisms have enzymes capable of digesting these bacteria which contain artificially synthesized D isomer amino acids As stated previously, there exist 20 different amino acids varying in functional groups. The ones above are hydrophilic (water loving) and can be subdivided into further subcategories. Add of these molecules are polar and water soluble  Lysine, arginine and histidine are all basic amino acids with positive R groups  Glutamate and aspartate are both acidic amino acids with negative R groups  Serine, Threonine, Glutamine and Asparagine are all polar amino acids with no charged R groups The nonpolar, hydrophobic (water fearing) amino acids are alanine, valine, isoleucine, leucine, methionine, phenylalanine, tyrosine and tryptophan  These amino acids are water insoluble There are three special amino acids:  Cysteine contains a sulfhydryl group useful for forming disulphide bridges, which stabilizes the folding structure of proteins and is also involved with intra and inter crosslinking  Glyceine has 2 hydrogens on the alpha carbon. This is useful in making compact polypeptide chains  Proline has a rigid ring structure which is also useful in compacting These amino acids arrange themselves in various levels of organization to eventually form unique 3D structures which are called conformations.  Function is derived from 3D structure and 3D structure is derived from the amino acid sequence The primary (1°) level of structure is the sequence of amino acids forming the polypeptide chain  Peptides are between 20 and 30 amino acids in length  Polypeptides are 200-500+ amino acids long  Proteins are usually thousands of amino acids in length and have 3D structure The secondary (2°) level of structure of a protein comes from the interactions between the carboxyl and amino groups of the individual amino acids which are found on the backbone of the polypeptide chain  These interactions produce localized folding in certain regions of the polypeptide chain 2Side view Side viewNaveen Sooknanan McGill Fall 2011  The reactions are stabilized, noncovalent interactions forming α helices, β sheets and β turns o These intera
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