Proteins - an Overview

Proteins and life

  • Proteins are abundant in all organisms and are indeed fundamental to life.


    • The diversity of protein structure underlies the very large range of their function:

    1. Enzymes - biological catalysts
  • Most of the chemical reactions which occur in biological systems are catalyzed by enzymes, which are proteins*. (In fact, some RNA molecules, called 'ribozymes' have been shown to have catalytic activity, so that in fact not all enzymes are proteins.)
  • Enzymes are a central component of "cellular machinery". The rates of the reactions they catalyze are generally increased by the order of at least a million-fold.
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    2. Storage
  • Various ions, small molecules and other metabolites are stored by complexing with proteins; for example haemoglobin carries oxygen and iron is stored by ferritinin the liver.

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    3. Transport
  • Proteins are involved in the transportation of particles ranging from electrons to macromolecules. Iron is transported by transferrin; haemoglobin occurs in red blood cells, and so delivers oxygen from lungs to other tissues.
  • Some proteins form pores in cellular membranes through which ions pass; the transport of proteins themselves across membranes also depends on other proteins.

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    4. Messengers
  • Proteins are involved in the transmission of nervous impulses, by acting as receptors of small molecules which cross junctions separating nerve cells.
  • Within an organism, biological processes must be coordinated between cells in tissues and indeed between different organs. This is achieved by the signalling molecules called hormones; a number of hormones are proteins (for example insulin).
  • Proteins also act as hormone receptors.

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    5. Antibodies
  • The immune system depends on the production of antibodies: proteins which bind to specific foreign particles such as bacteria and viruses.

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    6. Regulation
  • Enzymes synthesize proteins by translating sequences of DNA, and this production can be promoted or repressed by other proteins, in complex feedback mechanisms.

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    7. Structural proteins
  • Some proteins have a structural role, providing mechanical support. The "skeleton" of a cell consists of a complex network of protein filaments.
  • On a larger scale, muscle contraction depends on the action of large protein assemblies.
  • Collagen is found in all multicellular animals, occurring in almost every tissue. It is the most abundant vertebrate protein; approximately a quarter of mammalian protein is collagen.

    • Protein Structure

  • Proteins are linear heteropolymers of fixed length..
  • The monomers are amino acids, and there are 20 types, which themselves have a range of chemical properties.
  • The linear chains fold into specific three-dimensional conformations, which are determined by the sequence of amino acids; proteins are generally self-folding.
  • The three-dimensional structures of proteins are therefore also extremely diverse, ranging from completely fibrous, to globular.
  • Protein sequences are encoded in DNA, the holder of genetic information.
    • * Protein structures can be determined to an atomic level by X-ray diffraction and neytron-diffraction studies of crystallized proteins, and more recently by nuclear magnetic resonance (NMR) spectroscopy of proteins in solution. However there are many proteins whose structures cannot yet be solved.
    The reason that this field is so important is that the structure of a proteins is of course intrinsically related to its function. Experimental structure determination, or structure prediction, aids the elucidation of protein function; conversely, synthetic protein sequences might be designed so that the protein performs a desired function.

    The study of protein structure is therefore not only of fundamental scientific interest in terms of understanding biochemical processes, but also produces very valuable practical benefits.
     

    Benefits- past, present and future

    Medicine

  • Drug Design - The understanding of enzyme function allows the design of drugs which inhibit specific enzyme targets for therapeutic purposes.
  • Design Protein - for example, a current area of research focusses on the engineering of insulin so that it dissociates into its active form more readily, and therefore would quicken the response if injected into a diabetic patient.
  • Mass production - Gene technology has also allowed the mass production of human insulin in microorganisms, for use in the treatment of diabetes.

    • Agriculture

    Just as therapeutic proteins and drugs can be produced for medical and vetinary purposes, so can knowledge of protein structure and function be used to treat diseases of plants, and to modify growth and development of crops; for example the production of "stay-ripe" fruits.

    Industry

  • Protein engineering has potential for the synthesis of enzymes to carry out various industrial processes on a mass scale.
  • Use of lipases for the industrial breakdown of fats.
  • Introduction of biological detergents, containing enzymes.

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    The manipulation of genes and their protein products

  • A typical cell synthesizes approximately 15,000 different proteins;
  • of these, about 2,000 are abundant, with over 50,000 copies present.
  • There are only minute amounts of the remainer.
  • The traditional problems of protein research, i.e. purification of minute homogenous quantities from tissues, have been conquered with the advent of recombinant DNA technology.

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