A short time ago
Ask me this question.
The cell membrane contain bilayer (Explain)?
My answer was as follows
- because bilayer lipid is semi-permeable and allow only certain molecules to diffuse through the cell membrane
But he told me that your answer is wrong and the correct answer is as follows
-their polar phosphate molecules (hydrophilic) plasen in top and bottom surface of bilayer and non polar lipid (hydroplobic) lies between
For specialists:Which of the two answers is correct or both are correct?
With clarification please
Dear Bahha Habeeb ,
The answers are both right and, in a way, both wrong as well. It is a matter of a somewhat ‘sloppy’ description in the initial question. Indeed here https://www.genome.gov/genetics-glossary/Cell-Membrane they state, “The cell membrane consists of a lipid bilayer that is semipermeable.”
A way better description is “The cell membrane consists of a lipid bilayer, made up of two layers of phospholipids with cholesterols (a lipid component) ... The membrane also contains membrane proteins, including integral proteins that span the membrane and serve as membrane transporters, and peripheral proteins …” and (one of the functions is) “The cell membrane controls the movement of substances in and out of cells and organelles, being selectively permeable to ions and organic molecules.” https://en.wikipedia.org/wiki/Cell_membrane
So, a bilayer of (phospho-)lipids is the main ‘principle’ of how the cell membrane is built and this a whole world by itself, see for example https://en.wikipedia.org/wiki/Lipid_bilayer Again, in a way both answers tell a part of the whole story but it is essential to be fully clear where they refer to: either the cell membrane (with proteins included) or a (pure) lipid bilayer.
By the way the world famous “fluid mosaic model” by Singer and Nicolson: Singer, S. J., & Nicolson, G. L. (1972). The Fluid Mosaic Model of the Structure of Cell Membranes: Cell membranes are viewed as two-dimensional solutions of oriented globular proteins and lipids. Science, 175(4023), 720-731 remains useful as basic concept but new experimental findings/phenomena like the asymmetry of the bilayer, lipid rafts etc. reveals that the cell membrane is way more complex, see for example: Bernardino de la Serna, J., Schütz, G. J., Eggeling, C., & Cebecauer, M. (2016). There is no simple model of the plasma membrane organization. Frontiers in cell and developmental biology, 4, 106.
So, the seemingly simply question is way more complicated to answer correctly.
Best regards.
Dear Dr. Bahha Habeeb:
I totally agree with Dr. Rob Keller.
Even though, in order to condense the information he has provided, we could say that cell membrane is indeed a bilayer, through which can passively diffuse molecules, thus balancing concentrations of those compounds on both sides of the bilayer.
Even though, as the cell often needs that concentrations of some compounds to be different at both sides of the membrane, the cell membrane also has mechanisms of active transport of molecules, allowing the cell to maintain very different concentrations of some chemicals between the both sides of the bilayer, thus offsetting the effect of passive transport, which tends to equalize concentrations on both sides.
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