3. How doe bloodstream from the small intestine to cells? Be sure to address eac

Question

3. How doe bloodstream from the small intestine to cells? Be sure to address each molecule and the structure used to transport it in detail. [3 pts s the human body transport the component molecules that are not readily soluble in the 4. Once delivered to a cell, these molecules usually need to be moved into the cell to be used. Shown below is a representation of the phospholipid bilayer that makes up a considerable proportion of a cell membrane. Based on this structure, which of the component molecules would require help to cross a cell membrane and why? [1.5 pts] outside cel polar nonpolar polar inside cel

Explanation / Answer

3. There are multiple ways in whch those molecule got transported. the details of those processes are as follow:

a) Passive Diffusion : The simplest mechanism by which molecules can cross the plasma membrane is passive diffusion. During passive diffusion, a molecule simply dissolves in the phospholipid bilayer, diffuses across it, and then dissolves in the aqueous solution at the other side of the membrane. No membrane proteins are involved and the direction of transport is determined simply by the relative concentrations of the molecule inside and outside of the cell. The net flow of molecules is always down their concentration gradient—from a compartment with a high concentration to one with a lower concentration of the molecule.

b) Facilitated Diffusion and Carrier Proteins: Facilitated diffusion, like passive diffusion, involves the movement of molecules in the direction determined by their relative concentrations inside and outside of the cell. No external source of energy is provided, so molecules travel across the membrane in the direction determined by their concentration gradients and, in the case of charged molecules, by the electric potential across the membrane.

Two classes of proteins that mediate facilitated diffusion are generally distinguished: carrier proteins and channel proteins. Carrier proteins bind specific molecules to be transported on one side of the membrane. They then undergo conformational changes that allow the molecule to pass through the membrane and be released on the other side. In contrast, channel proteins form open pores through the membrane, allowing the free diffusion of any molecule of the appropriate size and charge.

c) Ion Channels : In contrast to carrier proteins, channel proteins simply form open pores in the membrane, allowing small molecules of the appropriate size and charge to pass freely through the lipid bilayer. One group of channel proteins, discussed earlier, is the porins, which permit the free passage of ions and small polar molecules through the outer membranes of bacteria.

d) Active Transport Driven by ATP Hydrolysis: The net flow of molecules by facilitated diffusion, through either carrier proteins or channel proteins, is always energetically downhill in the direction determined by electrochemical gradients across the membrane. In many cases, however, the cell must transport molecules against their concentration gradients. In active transport, energy provided by another coupled reaction (such as the hydrolysis of ATP) is used to drive the uphill transport of molecules in the energetically unfavorable direction.

Related Questions

Navigate

• Browse (All)
• Browse 3
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.