U2.5 cell Membranes

Word :

Cell membrane cell membrane

A very thin membrane, composed of lipids and protein, that surrounds the cytoplasm of a cell and controls the passage of S Ubstances into and out of the cell.

Defined:

The boundary of the cell. There are lipid, protein, a small amount of carbohydrate, surrounded by cytoplasm, control the inside and outside of the cell material.

cell membrane Composition :

Lipid 50%, protein 40%, sugar 2%-10%.

One of the most abundant phospholipids.

The more complex the cell membrane, the more the type and number of proteins.

Cancer and cell membranes

The malignant proliferation and metastasis of cancer cells were related to the change of cell membrane composition and the production of AFP, CEA.

AFP and CEA abnormalities in blood tests indicate that the cancer cells are present.

cell membrane function :

1. Isolate the cells from the outside world and keep them stable.

2 controlling substances in and out of cells

Antibodies, hormones, and waste are synthesized in cells, secreted outside the cell, but important substances such as nucleic acids are not lost outside the cell.

Some harmful substances in the environment may enter, and some viruses and germs can invade the cells, causing the organism to become sick.

3. Inter-cell information exchange

The diversity of communication means that multicellular organisms are a busy and orderly cellular society. Without cell communication, organisms cannot complete life activities as a whole. Most of the intercellular information exchange is related to the structure and function of cell membrane.

Plant cells also have a layer of cell wall outside the cell membrane, and its chemical composition is mainly cellulose and pectin. Cell walls have a supportive and protective effect on plant cells.

Cell membrane Structure:

It is a double-molecule layer of phospholipids, which is composed of two layers of phospholipids, which are made up of various types of membrane proteins and sugar and sugar lipids that bind to membrane proteins. The primary membrane is an important channel for the exchange of material and information between the cell and the surrounding environment and the cells and cells. The primary membrane through its pores and the transmembrane proteins of certain properties, to achieve a selective, controllable material transport.

1972, the mobile mosaic model, the American University of California, Singh (S. J. Singer) and Nixon (G. L. Nicolson) proposed.

The mobile mosaic model (Fluid Mosaic models) is currently the most widely accepted and recognized view. This view argues that the protein and lipid molecules that make up the membrane have a mosaic relationship, and that the membrane structure is in flux. Many experimental results support the model of the mobile mosaic model.

structure

In the theory of flow mosaic model, the phospholipid molecule in the membrane is arranged in a double layer, which forms the net frame of the membrane and is the substrate of the membrane. The phospholipid molecule is a bisexual molecule, which is divided into the hydrophilic head end and the hydrophobic tail end, the tip of the double-layer phospholipid molecule is toward the water phase, and the hydrophobic end is 22-phase buried in the membrane. The structural asymmetry of the inner layer (facing the surface of the cytoplasm) and the outer layers (facing the outside face) of the hydrophilic head end of the lipid bilayer molecule is mainly due to the different chemical compositions of the two hydrophilic heads.

Another major ingredient of the membrane is protein, some of which are embedded in the lipid double-decker grid, while others adhere to the lipid-bilayer surface . Depending on the location of the membrane, the membrane protein can be divided into two categories, one is strong hydrophobic or hydrophilic action with the membrane grease firm combination is not easy to separate, called the Integrated protein (Integral protein) or membrane intrinsic protein, the second is attached to the surface of the membrane, and the membrane is easy to separate, Called Membrane peripheral protein (peripheral protein) or external protein.

U2.5 cell Membranes