Cell Protein

2 Key excerpts on "Cell Protein"

• 

  eBook - ePub

  Fundamentals of Protein Biotechnology

  • Stein(Author)
  • 2017(Publication Date)
  • CRC Press

    (Publisher)

  In some proteins there can be further association of these units into dimers, tetramers, etc., and other hierachical arrangements which are referred to as the quaternary structure. The biological activity of a protein is totally dependent on the integrity of its three-dimensional structure. The folding of the polypeptide chain or the association of folded subunits defines a surface region which serves as the binding or active site through which proteins as well as other biosolutes interact via electrostatic forces, hydrogen bonds, hydrophobic Lipshitz and van der Waals forces, or covalent bonds to effect their biological actions. Proteins as biological effectors, as distinct from structural proteins, such as collagen and keratin, can be divided into six major groups. These are: 1.  Enzymes: Protein catalysts which mediate and accelerate the rate of biological reactions. 2.  Regulatory proteins: Hormones, lymphokines and growth factors which interact with membrane receptors to regulate cellular function. 3.  Receptors: Proteins on the cell membrane which interact with regulatory proteins and initiate the intracellular biochemical events which account for the biological response. 4.  Immune proteins: Proteins synthesized by cells of the immune system to bind to foreign substances or organisms and initiate a series of biochemical and cellular events leading to their destruction and removal. 5.  Carrier proteins: Ligand binding proteins which function intracellularly and extracellularly to create reservoirs of biologically important substances. 6.  Contractile proteins: Highly specialized proteins which transfer biochemical energy to cellular movement. In biological systems proteins from these groups are arranged into intricate intercommunicating networks through which the organism identifies and responds to changes in its internal and external environment. In this chapter we examine in detail some of these protein effector systems

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  eBook - ePub

  Protein Actions

  Principles and Modeling

  • Ken Dill, Robert L. Jernigan, Ivet Bahar(Authors)
  • 2017(Publication Date)
  • Garland Science

    (Publisher)

  CHAPTER

  2

  Proteins Perform Cellular Functions

  PROTEINS CARRY OUT MANY ACTIVITIES IN THE CELL

  Imagine a device that performs some chemical or physical action in a repetitive, self-sustaining way. Consider the basic requirements for such a device. It needs to take in raw materials, eliminate its waste, transduce the energy it needs, and transport or create a product. An advanced version of the device might seek its own supplies and energy, so it would need mobility and sensory and regulation systems. An even more advanced version would be self-sustaining beyond its component’s lifetimes. It would need to detect and repair its own broken parts, and even perhaps replicate itself, requiring memory, blueprints, and a way to translate blueprints into new component parts.

  Biological cells are such devices. And most of those functions are performed by proteins. Some proteins burn fuel (metabolic enzymes), some convert light to energy (rhodopsin and the photosynthetic reaction center), some serve as batteries to run chemical processes (ATPases), some carry oxygen (globins) to locations that burn the fuel, some store and transport energy (cytochromes), some enable the channeling of ions or transport of molecules across membranes (ion channels and transporters), some form the structural infrastructure (collagen and keratin), some transduce energy to motion (actin, myosin, kinesin, and dynein), some copy the DNA and RNA blueprints (polymerases), some repair the DNA and RNA blueprints (ligases and exonucleases), some eliminate old or broken components (nucleases and proteases), some control, regulate, and signal to keep the system functioning smoothly (transcription factors, hormones, receptors, and kinases), and some (immunoglobulins and cytokines) provide defense against invaders [1 ].

  The functionalities of proteins are listed in the Gene Ontology (GO) database (http://www.w3.org/1999/xlink [2 ]). In GO, each protein is described with three different descriptors: its molecular function , its biological process , and its cellular compartment or localization within the cell. For example, the molecular function of cytochrome c is oxidative reduction; the biological processes in which it is involved are apoptosis (programmed cell death) and oxidative phosphorylation, and its cellular localizations are in the mitochondrial matrix and inner membrane, although it can also be released to the cytoplasm, which is viewed as a point of no return for initiating apoptosis. lists the biological processes and molecular functions for the proteins in the human genome, as deduced from the human genome DNA nucleotide sequence of

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