Intracellular metabolic machinery

Recent reviews pertaining to such topics as the role of calcium in growth control (82), lectins as natural membrane components (83), fibronectins (84), and biochemical studies of the cell cycle (85, 86, 87, 88), together with many of the works cited earlier, suggest a dynamic, time-dependent relationship between extracellular factors, membrane components and the intracellular metabolic machinery as a cell goes from... 

Intracellular uptake of glucose itself raises certain problems. How is metabolic breakdown of glucose prevented if passage of the sugar from the lumen to blood proceeds via an intracellular route Do transporting cells contain diffusion barriers to prevent access of glucose to the metabolic machinery The metabolism-linked membrane permeability mechanism, used by certain other cells (2, 41), would be self-defeating in this case. 

Viruses are small infective agents consisting essentially of nucleic acid (either RNA or DNA enclosed in a protein coat). Some viruses contain additional lipoproteins, which may contain antigenic viral glycoproteins. Viruses are intracellular parasites with no metabolic machinery of their own. To replicate, they must attach to and enter the living host cell animal, plant, or bacteria and use its metabolic process. 

The intracellular PHA depolymerase system can act very efficiently in MCL PHA producers. Carbon limitation often leads to extremely rapid depolymerization. The diversity of metabolic machinery among PHA-accumulating microorganisms indicates that unusual and potentially valuable PHA copolymers await discovery. 

Viruses act as self-reproducing intracellular parasites. Although they have no metabolic machinery of their own and are unable to generate ATP or synthesize proteins, they are able to penetrate living cells and put the cell s metabolic machinery to their own use, causing it to manufacture new virus particles instead of normal cell products. Viruses contain either DNA or RNA but not usually both. The nucleic acid that carries the information that instructs the host cell to produce new virus particles is enclosed by a protein coat which protects it from mechanical breakage and enzymic attack. The coat also determines the specificity of the virus, i.e. the nature of the cell that the virus can infect. Bacteria may be infected by viruses known as bacteriophages. 

GH clearly has effects on carbohydrate and lipid metabolism, the protein-synthetic machinery, expression of specific proteins, and cell differentiation and proliferation. For a hormone concerned with the overall control of somatic growth such a wide spread of activities is potentially physiologically meaningful. It is at least possible that GH mediates these various actions via several different intracellular mechanisms and that it will not be possible to identify any one action as of key importance. 

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