Yeast reproduction

The converted mash is pumped to a clean sterilised fermentor and the yeast inoculum is added. The set temperature range for whiskey fermentation of 72 hours is usually 17—21°C. At the beginning, the mash converted composition is approximately 80% sugars, mainly maltose and some (<1%) dextrose (primary conversion). The pH is adjusted to reduce initial bacterial growth. Grain neutral spidts are usually set at 27—29°C to expedite fermentation. Temperatures above 35°C inhibit yeast reproduction and promote rapid bacterial growth. Above 40°C actual yeast kill occurs. 

This type of autocatalytic reaction is a simplification of many biological reactions such as fermentation, where the reaction produces products (species B in the previous example), which accelerates the rate. In fermentation, yeast cells in the solution produce enzymes that catalyze the decomposition of sugar to produce ethanol as a byproduct of yeast reproduction. Since the yeast population increases as the reaction proceeds, the enzyme concentration increases, and the process appears to be autocatalytic. A highly simplified description of fermentation might be... 

Yeasts belonging to Basidior cetes form external spores. ia.yiscomjcetes sexual reproduction occurs with the formation of spores in a cell that serves as a spore sac or ascus. Generally four, but sometimes eight or more, spores are formed in each ascus. This is sometimes reflected in the species name, ie,... 

Physiological Role of Citric Acid. Citric acid occurs ia the terminal oxidative metabolic system of virtually all organisms. This oxidative metabohc system (Fig. 2), variously called the Krebs cycle (for its discoverer, H. A. Krebs), the tricarboxyUc acid cycle, or the citric acid cycle, is a metaboHc cycle involving the conversion of carbohydrates, fats, or proteins to carbon dioxide and water. This cycle releases energy necessary for an organism s growth, movement, luminescence, chemosynthesis, and reproduction. The cycle also provides the carbon-containing materials from which cells synthesize amino acids and fats. Many yeasts, molds, and bacteria conduct the citric acid cycle, and can be selected for thek abiUty to maximize citric acid production in the process. This is the basis for the efficient commercial fermentation processes used today to produce citric acid. 

Bertsche U. 1978. The response of diploid yeast to radiations at different LET I. Potentially lethal and lethal damage to reproductive capacity. Radiat Res 76 349-367. 

The consequences of histone HI elimination in Tetrahymena and in the three species of fungi are consistent with the interpretation that linker histones do not have a role which is essential for the normal life-cycle of these organisms including sexual reproduction. Indeed, it has been reported that in yeast the HI occurs with a stoichiometry of about one molecule per 37 nucleosomes showing a preferential association with rDNA sequences [126]. The analyses of the effects of HI loss on transcription, particularly in Tetrahymena and yeast, provide strong... 

Computer] In fermentation processes sugar (AJ is converted to ethanol (C) as a byproduct of yeast (B) reproduction. In a simple model we can represent this process as... 

A number of other, more specialized systems are available to the reproductive toxicologist to answer specific mechanistic questions. In particular, the hormonal control of reproductive function and its perturbation by toxicants have received much attention. Such investigations can use intact cells to investigate the downstream consequences of toxicants on hormone-receptor interactions or use cells that respond to specific hormones (e.g., the MCF-7 breast cancer cell line and estrogen Soto et al., 1995). Receptor biology/ligand binding can be examined in membrane preparations of specific cell types or in recombinant cell systems (e.g., human and yeast cells Klein et al.,... 

Essential to ascidians ("sea squirts"), which concentrate in a miilionfold from sea water. Essential to chicks and rats. Deficiencies cause reduced growth, impaired reproduction and sirvival of young, impaired tooth and bone metabolism and feather development.4 May be a factor in manic-depressive illness/ Essential involved in gkicose metabolism and diabetes potentiates effect of insulin. Presence in glucose tolerance factor from brewer s yeast questioned/... 

The overall life cycle of a particular yeast Saccharomyces (S.) cerevisiae, is summarised in Fig. S.6 which shows how it is possible for the cells to fuse to form various cell and spore types. The figure shows the possible types of reproduction in yeast. Generally, industrial strains of S. cerevisiae, brewers yeast, reproduce by budding/ fission processes and only sporulate under specialised conditions. However, many strains of yeast are capable of cell fusion to form spores or cells with increased genetic complements. Such strains have many sets of chromosomes and are termed polyploid. Active fermentation of industrial strains involves growth by mitotic division and nutrient depletion which results in stationary cells with little or no spore formation. 

In addition to the limited number of expressed genes, bacteria feature a highly reproductive cycle but no cell nucleus, no organelles for compartmentation, no cell-to-cell communication as in tissues, and quite a straightforward metabolism. Favored bacterial systems for production of recombinant proteins are various strains of E. coli, Bacillus, and Pseudomonas. Non-bacterial options such as yeast or mammalian cells are discussed briefly later in this chapter. 

The molecular phylogeny and systematics of the fungi will be discussed elsewhere in this book [13]. A simple division of fungi with respect to clinical aspects is that into molds and yeasts, the former characterized by the formation of septate and nonseptate hyphae, the latter by an unicellular life cycle with reproduction mainly by budding. The so-called dimorphic fungi, such as Histoplasma... 

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