Question

Explain the questions detailed. 10 pts each

1. In which compartment you would find a low concentration of both K+ ions and Proteins and why?

2.  In a given molecule which are the determinants for its transport through a membrane (active/passive/receptor mediated etc.) ?

Answer 1

1. In the intracellular compartment there is more concentration of protein and potassium ion, Sodium potassium pump is responsble for high concentration of potassium which actively transports sodium out of and potassium into the cell at a ratio of 3:2

2 Some molecules can diffuse through the cell membrane without any assistance from the cell. Others require the help of transmembrane proteins to move into or out of the cell. Primary factors which determine whether a molecule will diffuse across a cell membrane are concentration, charge and size.

The primary determinant of whether a molecule will diffuse across a cell membrane is the concentration of the molecule on each side of the cell membrane. For example, the extracellular concentration of oxygen is higher than the intracellular concentration, which is why oxygen diffuses into the cell and carbon dioxide diffuses out. Small molecules can easily pass through while it is harder for large molecules to pass through, for example sugar molecules cannot pass through easily because of their large size they require the help of transmembrane protein to pass through.  Cell membranes prevent charged molecules from entering the cell unless the cell maintains an electrical potential.

Passive transport such as diffusion and osmosis, moves materials of small molecular weight across membranes.without use of energy, In passive transport, substances move from an area of higher concentration to an area of lower concentration. Sometimes, molecules cannot move through the cell membrane on their own. These molecules need special transport proteins to help them move across the membrane, a process known as facilitative diffusion.These are called channel protein or carrier protein, . Channel proteins are specific for the molecule they transport,for example a sodium ion crosses the membrane through a channel protein specific for sodium ions.

Active transport : Active transport moves molecules against their concentration gradient, from an area of low concentration to an area of high concentration, with the help of energy, ATP is the most common source of energy for active transport, as molecules are moving against their concentration gradients, active transport cannot occur without assistance, they use pumps for their assistance, The sodium-potassium pump uses ATP to move three sodium ions and two potassium ions to where they are already highly concentrated. Sodium ions move out of the cell, and potassium ions move into the cell.There are two types of active transport: primary active transport that uses adenosine triphosphate (ATP), and secondary active transport that uses an electrochemical gradient.

Bulk transport : The movement of macromolecules such as proteins or polysaccharides into or out of the cell is called bulk transport. There are two types of bulk transport,receptor mediated exocytosis and endocytosis, and both require the expenditure of energy (ATP).

Receptor-mediated endocytosis is a form of endocytosis in which receptor proteins on the cell surface are used to capture a specific target molecule, when the receptors bind to their specific target molecule, endocytosis is triggered, and the receptors and their attached molecules are taken into the cell in a vesicle. Sometimes Flu viruses, d and cholera toxin all use receptor-mediated endocytosis pathways to gain entry into cells.