Cell growth cycle

Proteins also serve as chemical signals in the body. At the level of organ systems, proteins regulate immune responses, cell growth cycles, hormone responses, and many other functions. Blood proteins are involved in coagulation and dissolution of blood clots. Several hormones are short proteins, or polypeptides. Many polypep-... 

Product formation can take place during different phases of the cell growth cycle. When product formation only occurs during the exponential growth phase, the rate of product formation is... 

In batch fermentation, the number of cells of the microorganism present in the reactor typically varies with time in the manner shown in Figure 13.1. Readers should note that the scale of the ordinate is logarithmic while that of the abscissa is linear. Some authors describe the cell growth cycle shown in Figure 13.1 in terms of the four primary phases, while others include two smooth transitions between primary phases as additional growth phases. 

Grzelak, A., Janiszowska, W., 2002. Initiation and growth characteristics of suspension cultures of Calendula officinalis cells changes in the level of oleanoUc acid during the cell growth cycle of the culture. Plant Cell Tissue Organ Cult. 71, 29-40. 

The last part of this account will be devoted to protein kinases and protein phosphatases and some recent results we have obtained for them. Protein kinases and phosphatases are signaling biomolecules that control the level of phosphorylation and dephosphorylation of tyrosine, serine or threonine residues in other proteins, and by this means regulate a variety of fundamental cellular processes including cell growth and proliferation, cell cycle and cytoskeletal integrity. 

Product formation kinetics in mammalian cells has been studied extensively for hybridomas. Most monoclonal antibodies are produced at an enhanced rate during the Gq phase of the cell cycle (8—10). A model for antibody production based on this cell cycle dependence and traditional Monod kinetics for cell growth has been proposed (11). However, it is not clear if this cell cycle dependence carries over to recombinant CHO cells. In fact it has been reported that dihydrofolate reductase, the gene for which is co-amplified with the gene for the recombinant protein in CHO cells, synthesis is associated with the S phase of the cell cycle (12). Hence it is possible that the product formation kinetics in recombinant CHO cells is different from that of hybridomas. 

For type 3 processes, growth and metabolic activity reach a maximum early in the batch process cycle (Figure 3.1) and it is not until a later stage, when oxidative activity is low, that maximum desired product formation occurs. The stoichiometric descriptions for both type 3 and 4 processes depend upon the particular substrates and products involved. In the main, product formation in these processes is completely uncoupled from cell growth and dictated by kinetic regulation and activity of cells. 

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