Question

how do ABC transporters and P-type ATPases work to pump drugs and Ca²⁺

what are the major steps and molecules in clathrin-mediated endocytosis

how does negative and positive feedback regulation work in a simplistic kinase cascade and predict how changes in one kinase’s activity would affect another

Answer 1

Viruses can enter the cell in a variety of ways, either through direct membrane fusion/penetration reactions at the plasma membrane, or by undergoing endocytosis followed by similar breaching of the cell membrane in an early endosome.

Endocytosis is a process by which a vesicle buds off from the cell membrane to be released into the cytosol. As the initial step in the shuttling events of vesicles from the plasma membrane and between endosomal compartments; this process modulates several essential cellular functions.

Clathrin-mediated endocytosis (CME) requires assembly of a protein coat on the membrane in order to induce curvature and form a spherical invagination.Besides the scaffolding protein clathrin some key factors implicated in CME include Epsin,Eps15, Ampiphisin,Adaptor protein 2(AP2), Dynamin,Actin, and the phospholipid phosphatidylinositol 4,5-bisphosphate(PIP₂).

In the case of endocytic trafficking from the plasma membrane, these proteins co-localize and complex on the cytosolic side of the plasma membrane to form coat at the site of endocytosis. The phospholipid PIP₂ which makes up less than 1 percent of all lipids, has been shown to localize to endocytic sites in high concentrations,where it binds a variety of membrane proteins. The process of CME can be seperated into several steps, which include: 1) the nucleation of a clathrin coated pit(CCP) 2) cargo capture in coated pits 3) curvature induction and membrane invagination 4) vesicle scission and uncoating.

ABC transporters are active transporters,they use energy in the form of ATP to translocate substrates across cell membranes.The transport protein contains an ATpase, which hydrolyzes ATP to generate the energy required for transport(Ion pump). Substrates of ABC transporters are lipids and sterols,ions and small molecules, drugs and large polypeptides.

P-type ATPase are family of transport enzymes which pump cations across the membrane using primary active transport.The solute carrier family includes transporters that function by secondary active transport and facillitate diffusion.They are located on cell membranes as well as on the intracellular membrane of organelles.

Protein kinases are enzymes that regulate the biological activity of proteins by phosphorylation of specifi amino acids with ATP as source of phosphate, thereby inducing conformational change from inactive to active form of protein.

These activities are regulated by stimuli which participates in controlling protein kinases activities.