Dynamic Changes In Lipid Composition

Structural Variability in Clam Cell Membranes: Differences between Different Yeast Strains Name : Minggu Menang Class : 19-A The yeast is a member of the Kingdom Fungi that most or all of its life cycle is in a single cell condition. Yeast is not an official taxonomic group and its grouping is based on its life form. Other members of Fungi that are also grouped based on the same characters are molds and fungi. The yeast cell is one of the models of eukaryote cells because it has the characteristics of this cell type: it has subcellular compartments that create organelles such as the nucleus, mitochondria, Golgi apparatus, and others. Cell membrane Yeast has a cell membrane with a thickness of 7.5 nm which is two layers of lipids interspersed by globular proteins and forms a fluid mosaic. The lipid component consists of phospholipids that play a role in membrane fluidity, and sterols that play a role in membrane rigidity. While the protein components that intersperse the lipid layer consist of proteins that play a role in substance transport, cell wall biosynthesis, signal transduction, and cytokeleton attachment. The structural components of cell membranes vary greatly between species, and even different strains within a single species can have variations in membrane lipid composition. For example, a baker yeast strain of Saccharomyces cerevisiae has a much lower amount of phosphotadylcholine (a phospholipid component) than a brewer yeast strain of the same species. These differences in cell membrane composition are not static characteristics, but dynamic depending on the growth conditions of the yeast. The yeast cell membrane is selectively permeable, i.e. able to select substances that can pass through, so its function is mainly in regulating the entry and exit of substances from and into the cytoplasm. An important role of the membrane is related to the nutritional process of the yeast, such as the process of taking carbohydrates, nitrogen compounds or ions; as well as the removal of harmful substances from the cell. Other roles include endo- and exocytosis of complex molecules, conducting signals from outside the cell in the process of cell response to the environment, and sporulation. Periplasm The periplasm is a 35-45 Å thick "empty" region between the cell membrane and the cell wall. The periplasm contains secretory proteins (mannoproteins) that are unable to penetrate the cell wall, including enzymes that hydrolyze substrates that are unable to pass through the cell membrane, including invertase, acid phosphatase, melibiase, and trehalase. Cell wall The yeast cell wall is a thick structure (100 - 200 nm) containing 80 - 90% polysaccharides, mostly glucan and manan and a little chitin. Glucan will form a network of microfibrils while manan generally binds to proteins to form mannoproteins. Chitin, a polymer of Nacetylglucosamine, is only found in very small amounts (2 - 4%) in the sell wall. However, in yeasts that are able to form hyphae, the amount of chitin is higher. In addition to polysaccharides, the cell wall of yeast also contains proteins, lipids, and inorganic phosphates. The yeast cell wall is a layered structure: at the outermost layer there is mannoprotein; then a network of glucan microfibrils; then chitin and mannoprotein in the innermost layer. Mannoprotein functions as a determinant of cell wall porosity and will "reject" the entry of molecules larger than 600 kDa, glucan functions to maintain cell wall rigidity, while chitin functions, among others, as a mycosine receptor and maintains cell osmotic integrity.