Up regulation and down regulation with examples

Down regulation

o   Is the process by which a cell decreases the quantity of a cellular component, such as RNA or protein in response to an external variable.

o   There are several ways in which a cell down regulates its cellular components.

1.      Receptor mediated endocytosis.

Occurs when the material to be transported into the cell binds to certain specific molecules in the membrane. Common cause for down regulation in membrane receptor. 

2.      Internalization.

Ligands bind to their receptors and ligand-receptor complex move laterally in the membrane to coated pits where they are taken into the cell by endocytosis. Some receptors are recycled and some replaced by de nova synthesis. 

The main characteristics of the erythrocyte cell membrane and relate these to the function of erythrocyte.

Organization of erythrocyte membrane

 

Human erythrocytes are small cells that lack nuclei when mature they appear as circular biconcave discs.

• The membrane structure agrees with the Fluid Mosaic Model.
• “the membrane protein ,intrinsic proteins(integral) deeply embedded and peripheral proteins loosely attached, that in an environment of fluid phospholipid bilayer.”
• Fluidity of the membrane largely depends on the lipid composition of the membrane
•  Due to presence of phospholipids erythrocyte membrane has high fluidity & flexibility.
  

The main sub cellular features of a protein secreting cell.

o   A protein secreting cell is metabolically very active

o   It receives signals via G protein coupled receptors.

o   It has a prominent nucleus which takes a large space of the cell. (Transcription, translation occurs in it.)

o   RER supports in synthesis of protein. So it is prominent in the cell. (RER has ribosome on its surface which involve in polypeptide synthesis using amino acids)

o   More mRNA, tRNA & rRNA make cytoplasm basophilic.

o   From RER synthesized polypeptides sent to Golgi apparatus for further modifications via vesicles. So large number of vesicles can be seen.

o   Well developed Golgi apparatus can be seen for post translational modifications of synthesized polypeptides.

o After that finished proteins exit from the cells by a secretory vesicles made out of Golgi apparatus, so large number of secretory vesicles can be seen.

The transport mechanism of monosaccharides across the intestinal mucosal cells.

o   Monosaccharides are formed by single saccharide molecules.

o   We normally talk about glucose, fructose & galactose as monosaccharides. There are so many except these three.

o   When we talk about starches, they are digested to various types of monosaccharides, disaccharides by gut enzymes secreted from various organs like pancreas.

o   There are same enzymes which digest disaccharides to monosaccharides. They are placed on brush border of the mucosal cells. Isomoltase, Moltase, Sucrose.

o   After the digestion final product is monosaccharides & they are transported across the intestinal mucosal cells to the portal system by various transport mechanisms.

How G protein help in signal transmission in to the cell from an incoming ligand & outline the steps.

• Ligand bind G protein coupled receptor which has α ,β & γ subunits.
• After binding, GTP in α dissociates from β & γ( all 3 subunits can produce physiological effects)
• Causes production of a 2^nd messenger eg:-cAMP via activation of adenylyl cyclase.
• cAMP produce activated protein kinase A( pK_A)  à  pK_A phosphorylate certain molecules & activate /inhibit  à brings about the physiological action
• When work is done , intrinsic GTPase activity of GTP-α converts GTP to GDP   à α ,β & γ subunits reassociates  à action terminates.