Module 2 - Case

Module 2 - Case

First Construction of cell membranes 

They have a continuous structure, are composed of lipids and proteins (about the same weight of the two components).  Phospholipids - form bilayer membranes in water, are liquid (building membrane lipid molecules move. Traffic is confined to the plane of the film - moving particles within a layer) Membrane fluidity depends on several factors. The most important of these is its lipid composition. In addition to phospholipids and glycolipids to membrane lipid components should also be cholesterol. It is immersed in a membrane constructed of lipid bilayer, so that the polar group-OH is directed towards the water surrounding the membrane, while the remainder enters the interior of the membrane. The presence of cholesterol alters the membrane - in areas where there is more, the film is less liquidity and its components are more difficult to move. The content of cholesterol in the membranes of individual cells varies greatly. 

Lipid molecules move in the plane of the film within the layer in which they are located. However, very rarely "jump" from one layer to another. Thanks to the two layers differ considerably lipid composition of lipids, glycolipids are located in this part of the membrane, which is directed outwards - this glycolipid sugar chains 'extend' the cell to the outside environment. 

Proteins are another important component of cell membranes. Some of them are attached to the membrane only because of their polypeptide chains are attached fatty acid chains or other non-polar portion that easily penetrates between the non-polar parts of the lipid. Other proteins in the membrane immersed their polypeptide chains (Think Quest, n.d.). These chains are arranged in such a way that they are exposed outside the group of non-polar amino acid side-thus can be immersed in a non-polar membrane lipid environment. 

Membrane proteins are immersed in the lipid layer in different ways: directed to one or other side of the membrane or pass through the whole film, projecting from both sides.  As lipids, proteins can perform limited movements in a plane, but can not move across the membrane. Cell membrane asymmetry thus relates to both its components: Each layer of the cell membrane has its own lipid composition and its own set of proteins. 

Proteins that are on the outer side of the cell membrane of eukaryotic cells are often attached to their polypeptide chains composed of sugar chains. Together with the chains which protects cell membranes against mechanical and chemical damage prevents some, not allowing many substances to the membrane. 

Ribosomes

These structures shape not separated from the matrix by any membrane. Components are ribosomal RNA and protein. They play an important role in protein synthesis. They consist of larger and smaller subunits.

Ribosomes can be divided into two types due to the place of occurrence: 70S ribosome smaller. It is found in prokaryotes and organelles of cells independent (mitochondria, plastids) large 80S ribosome occurs in the cytoplasm of the cells and are connected Eucariota of rough endoplasmic. Count depends on the activity of ribosomes cell. In prokaryotes the synthesis of ribosomes in the cytoplasm. However, Eucariota synthesize components (rRNA) needed to build ribosomes in the nucleolus , where he takes the process of ...