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... The nucleus houses most of the genetic material of the cell, DNA (there is some too in the mitochondria and plastids). Unless the cell is divided, the DNA is long and stringy and is not highly folded. ...
The endoplasmic reticulum is made of many folded membranes throughout the cell. ... One of the roles of the ER is to form membranes and to insert phospholipids or proteins which make up the membrane. The newly formed membrane is then exported as transitional ER to an appropriate site in the cell. ... Rough ER is covered in ribosomes which may produce antibodies or glycoproteins, which are secreted by the cell. ... Tiny vesicles are formed and pinched off the Golgi apparatus and then can attach to the cell membrane and release their contents by exocytosis.
Lysosomes contain hydrolytic enzymes (catalysts of hydrolysis reaction) which could digest the cell and must therefore be sequestered away. ... There are 4 ways in which the lysosomes function:
1) In damaged cells, lysosome membranes break releasing enzymes into cytoplasm. ...
2) Cell death during development. ... If a cell is actively involved in protein synthesis, it will contain many ribosomes. ... Bound ribosomes make proteins that are usually for export or for inclusion into membranes. ... They form long narrow tubes and provide support to the cell. ... They are therefore associated with movement of the cell and within the cell. ... They are involved in cell division. ... We will examine these organelles with an eye to their role at a molecular level in the cell, and leave descriptive cell biology for another course. For example, our interest in the mitochondrion lies in its ability to generate energy in a form that is useful to the cell, and to that end we are interested in how the membrane structure allows the energy generation to proceed. ... Mitochondria have two membranes, an inner and an outer, clearly visible in this electron microscope photo of a mitochondrion. ... The existence of this double membrane has led many biologists to theorize that mitochondria are the descendants of some bacteria that was endocytosed by a larger cell billions of years ago, but not digested. ... These sacs can be targeted at various locations in the cell and even to its exterior.
Lysosome
This organelle digests waste materials and food within the cell, breaking down molecules into their base components with strong digestive enzymes . Here we can see an advantage of the compartmentalisation of the eukaryotic cell: the cell could not support such destructive enzymes if they were not contained in a membrane-bound lysosome . ... They are the cell membrane, the cytoplasm, and the cytoskeleton. The cell membrane is so important that we devote the entire next module to it. ... All of these are absolutely necessary to the survival of the cell, and are spread randomly throughout the cytoplasm. ... The DNA of prokaryotes floats freely around the cell; the DNA of eukaryotes is held within its nucleus. ...
Cell Wall
Prokaryotes have a cell wall composed of peptidoglycan, a single large polymer of amino acids and sugar . Many types of eukaryotic cells also have cell walls, but none made of peptidoglycan.
Membrane Structure and Composition
Biological membranes are bilipid layers . In a real cell the membrane phospholipids create a spherical three dimensional lipid bilayer shell around the cell. ... This is known as the fluid mosaic model of biological membranes (mosaic because it includes proteins, cholesterol, and other types of molecules besides phospholipids). The phospholipids can move to the opposite side of a bacterial cell membrane in a few minutes at room temperature. ... Cholesterol is a necessary component of biological membranes. ... Therefore, one way for a cell to control the fluidity of its membrane is by regulating its level of cholesterol in the cell membrane.
Another way for the cell to control the fluidity of its membrane is to regulate the ratio of saturated to unsaturated hydrocarbon chains of the phospholipids.
Approximate Word count = 3196
Approximate Pages = 12.8
(250 words per page double spaced)
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