Question

Different types of cells have different types of integral membrane proteins. What would you expect to reside in the plasma membrane of an epithelial cell that might be absent from that of an erythrocyte? How do such differences relate to the activities of these cells? explain d in etail and give reference. (15points)

Answer 1

Membrane proteins represent about a third of the proteins in living organisms. Based on their structure, there are main three types of membrane proteins: the first one is integral membrane protein that is permanently anchored or part of the membrane, the second type is peripheral membrane protein that is only temporarily attached to the lipid bilayer or to other integral proteins, and the third one is lipid-anchored proteins

According to their their relationship with the bilayer, integral membrane protein can be classified two primary types: integral polytopic proteins and Integral monotopic proteins. Integral polytopic proteins are also known as “transmembrane proteins” which can span across the membrane at least once

the plasma membrane of the human erythrocyte membrane as an example of a plasma membrane. The mammalian erythrocyte has a simple structure compared to other eukaryote cells because it has no intracellular organelles (interestingly avian erythrocytes do have nuclei—mammalian erythrocytes become enucleated during maturation). The simple structure and the relative ease with which erythrocytes can be isolated from mammalian blood made the erythrocyte plasma membrane accessible for early studies of plasma membrane structure and function.

As all plasma membranes, the mammalian erythrocyte plasma membrane facilitates transport of nutrients. The plasma membrane of the human erythrocyte contains a membrane protein specific for the transmembrane movement of the cellular nutrient glucose. If this transport system is blocked, glucose transport into the cell is effectively blocked (and since the erythrocyte is too simple a cell to make ATP it is dependent upon obtaining glucose from the blood plasma). The protein responsible for glucose transport is a (transmembrane) protein embedded in the plasma membrane. Membrane proteins responsible for transport of molecules into or out of a cell are usually embedded in the membrane. Another example of transport is provided by one of the most abundant membrane proteins of the human erythrocyte membrane, the anion transport protein. This protein functions as a channel that specifically allows anions to move rapidly across the membrane. In erythrocytes, rapid chloride–bicarbonate exchange across the plasma membrane is functionally integrated with the binding and absorption of oxygen by hemoglobin inside the erythrocyte and in CO2 transport.

The inside and outside of the mammalian erythrocyte, as in the case in most cells, is distinctly different in ion composition. Sodium ion concentration is relatively low inside the cell and potassium ion concentration is relatively high inside the cell. Correspondingly outside the cell, sodium ion concentration is relatively high and potassium ion concentration is relatively low.The Na+ K+ ATPase, an enzyme (and transmembrane protein) of the erythrocyte plasma membrane, simultaneously pumps sodium ion out of the cell and potassium ion into the cell. The ion-pumping function of the Na+ K+ ATPase maintains the distinct difference in Na+ and K+ concentrations between the inside and the outside of the cell. The pump (the Na+ K+ ATPase) hydrolyzes ATP to provide the necessary energy for the transport process, to transport these ions against their respective concentration gradients.

In humans, mature red blood cells are flexible and oval biconcave disks. They lack a cell nucleus and most organelles, in order to accommodate maximum space for hemoglobin; they can be viewed as sacks of hemoglobin, with a plasma membrane as the sack.

The red blood cell membrane is composed of 3 layers: the glycocalyx on the exterior, which is rich in carbohydrates; the lipid bilayer which contains many transmembrane proteins, besides its lipidic main constituents; and the membrane skeleton, a structural network of proteins located on the inner surface of the lipid

Plasma membrane is made up of a two layers . This bilayer is composed of two layers of lipids (consists mostly of phospholipids and to a smaller extend of glycolipids). Glycolipids are generally found in the outside layer, whereas phospholipids are predominantly in the inside layer (cytoplasmic side). The other important component of the plasma membrane is protein. Proteins can be associated with the outside (peripheral) of the membrane or they extend throughout the entire membrane (transmembrane). Plasma membrane has 50-50% of both lipids and proteins

Epithelial cells form tightly cohering sheets whereas erythrocytes occur as single cells. type of integral proteins expect to reside in the plasma membrane of an epithelial cell that might be absent from that of an erythrocyte isproteins involved in cell-cell adhesion or cell-cell communication. the tightly cohering cells would definitely need effective cell to cell adhesion or communication for the epithelial cells to adhere into cohering sheets of cells. Erythrocytes because they exist a 'single cells' would probably not require too many of these types of proteins