S. cerervisiae

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Saccharomyces cerevisiae or S. cerevisiae is one of the many model organisms studied in laboratories all over the world. This is because its genome has been sequenced, its genetics easily manipulated, and it is easy to maintain in the lab. This species of yeast has been a vital resource in the comprehension of basic, essential cellular processes such as cell division and cell death. It is commonly known as Baker's yeast or Brewer's yeast and is found in the wild growing on the skins of grapes and various other fruits.

Contents

Classification

S. cerevisiae has a cell wall made of chitin and has no peptiodglycan in its cell walls, and its lipids are ester linked. Due to this, it is placed in the fungi kingdom. In addition, it also uses DNA template for protein synthesis and it has larger ribosomes.

Adaptations

S. cerevisiae has adapted in a number of important ways. One being, they are able to break down their food through both aerobic respiration and anaerobic fermentation. They can survive in an oxygen deficient environment for a period. The second is that they have the ability to have both sexual and asexual reproduction. Very few other Ascomycota can do both processes. Fewer organisms can do all four of these processes. This variety allows this species to live in many different environments.

Nutrition:

Obtain its energy from glucose (C6H12O6)

Life Cycle

S. cerevisiae has both asexual and sexual reproduction.

In asexual reproduction, the haploid of the yeast undergoes mitosis and forms more haploid yeasts. There is an a and ά strain of these haploids. Then these haploid yeasts, one from each strain, can fuse together and become a cell. Then the nuclei of both cell fuse together and this cell is now the zygote. These diploid cells can go through mitosis, which they call budding, and four more zygotes or they can undergo meiosis and from an ascus which will split into four ascospores. These haploids can then undergo germination and become haploid yeast again.


Uses/ Importance

Responsible for the production of ethanol in alcoholic drinks. That is where the names brewer’s and baker’s yeast come from. The process in which it produces ethanol is one way this yeast converts glucose into energy. There are two ways S. cerevisiae breaks down glucose. One way is through aerobic respiration. This process requires the presence of oxygen. When oxygen is not present the yeast will then go through anaerobic fermentation. The net result of this is two ATP, and it also produces two by-products; carbon dioxide and ethanol. So if this yeast is allowed to grow in a container lacking oxygen it will produce ethanol (alcohol). The yeast helps in the rising of bread with its other by-product carbon dioxide. The gas that is produced inside the dough causes it to rise and expand. Both of these processes use the haploid of this yeast for this process. In industry, they isolate one strain, either a or ά, of the haploid to keep them from undergoing mating. In the baker’s yeast, they have a strain where the production of carbon dioxide is more prevalent then ethanol and vice versa for brewing[1].

References

  1. J. Richard Dickinson, Michael Schweizer (2004) 'Metabolism and Molecular Physiology of Saccharomyces Cerevisiae', 2nd Edition
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