Is Cell Membrane Rigid: 11 Important Facts You Should Know


In this article, we get know about 11 Important Facts regarding ‘is cell membrane rigid‘ , functions and composition along with some key models of plasma/ call membrane.

The membrane that divides the cell interior from the external environment is known as the plasma membrane, sometimes known as the cell membrane, and it is present in all cells. Cell walls are externally joined to the plasma membrane in bacterial and plant cells. A semipermeable lipid bilayer makes up the plasma membrane. The passage of materials into and out of the cell is controlled by the plasma membrane.

Important points

  • The membrane can rupture if it is pierced or if a cell absorbs in too much water. It is both fluid and rather hard.
  • The plasma membrane is mosaic in nature, which enables a very small needle to readily pierce it without rupturing it and enables it to self-sealing when the needle is removed.
  • When temperatures drop, saturated fatty acids constrict and press against one another to form a dense, comparatively rigid membrane.
  • The “kinks” in unsaturated fatty acids’ tails push adjacent phospholipid molecules apart when they are flattened, maintaining the fluidity of the membrane.
  • The ratio of saturated to unsaturated fatty acids affects the membrane’s fluidity at low temperatures.
  • Cholesterol acts as a buffer, preventing both lower and higher temperatures from impairing fluidity.
is cell membrane rigid
The membrane of a eukaryotic cell is shown from Wikipedia

Let us discuss some facts and try to understand is the cell membrane rigid or flexible.

  1. Is the cell membrane rigid or flexible?
  2. Why is the cell membrane rigid?
  3. When is the cell membrane rigid?
  4. What does make a cell membrane rigid?
  5. What are the functions of rigid cell membrane?
  6. Do all cells have a rigid cell membrane?
  7. Is plant cell membrane rigid or flexible?
  8. Is bacteria cell membrane rigid or flexible?
  9. Is fungi cell membrane rigid or flexible?
  10. Can cell walls be semi rigid?
  11. Can cell walls be flexible?

Let us look these facts in details and get the answer to is the cell wall rigid or not.

Is the cell membrane rigid or flexible?

Thus, the interior of the membrane can move freely due to the lengthy hydrocarbon chains of the fatty acids, making the membrane itself flexible and supple. Furthermore, the ability of proteins and phospholipids to freely diffuse laterally inside the membrane is a crucial characteristic for many membrane processes.

is cell membrane rigid
A detailed diagram of the cell membrane from Wikipedia

Ex: components responsible for fluidity of cell membrane

  1. A number of elements affect membrane fluidity. First off, the mosaic structure of the membrane helps to keep the plasma membrane fluid.
  2. The membrane contains independent but loosely bound molecules of the required lipids and proteins. The cell membrane is fairly hard and can burst if pierced or if a cell takes in too much water, unlike a balloon that can swell up.
  3. The second reason for fluidity is due to the properties of phospholipids. The fatty acids in the phospholipid tails are in their saturated state, which is saturated with connected hydrogen atoms and free of double bonds between neighboring carbon atoms.
  4. The third element that keeps mammalian membranes fluid is cholesterol. It is located in the membrane close to the phospholipids and helps the membrane resist the effects of temperature changes.

Why is the cell membrane rigid?

So, the portions of the fatty acid chains close to the phospholipid head groups engage with the rigid heterocyclic rings of cholesterol. This interaction makes this region of the membrane relatively rigid by reducing the movement of the outside fatty acid chains.

When is the cell membrane rigid?

The membrane can rupture if it is breached or if a cell absorbs in too much water. It is both fluid and fairly rigid. The plasma membrane is mosaic in nature, which makes it easy for a very small needle to pierce it without rupturing it and enables it to self-sealed when the needle is removed.

What does make a cell membrane rigid?

The portions of the fatty acid chains close to the phospholipid head groups engage with the rigid hydrocarbon rings of cholesterol. This interaction makes this region of the membrane more rigid by reducing the mobility of the outside fatty acid chains.

Ex:

  • More specifically, the saturated or unsaturated profile of the fatty acids affects the fluidity of the membrane. Saturated fatty acids have the highest hydrogen content and the absence of double bonds in their hydrocarbon chain. The membrane seems to be more rigid and densely packed because there aren’t any double bonds.
  • The plasma membrane, like all other cellular membranes, is made up of both lipids and proteins. The phospholipid bilayer, which forms a transient barrier between two aqueous compartments, is the membrane’s primary structural component.

What are the functions of rigid cell membrane?

Large, highly charged molecules like ions and sugars and amino acids cannot diffuse through cell membranes. These chemicals can move through the membrane due to specialised transport proteins that are embedded there.

Ex:

  • Membrane transport proteins frequently require energy to catalyse passage, and they are specialised and selective for the molecules they move. These proteins also move some nutrients against the gradient of concentration, which demands more energy.
  • For cells to stay healthy and function properly, they must be able to sustain concentration gradients and occasionally move materials against them.
is cell membrane rigid
Illustration depicting cellular diffusion from Wikipedia

Other key functions

1. Passive osmosis and diffusion: Diffusion, a form of passive transport, allows some substances (small molecules, ions), including oxygen (O2) and carbon dioxide (CO2), to penetrate the plasma membrane.

2. Channels and transporters made of transmembrane proteins: These proteins penetrate the lipid bilayer of membranes and work on both sides of the membrane to move molecules across it.

3. Endocytosis: Endocytosis is the process by which molecules are taken up by cells and engulfed. The substance to be carried is caught in a little invagination that the plasma membrane forms that extends inward.

4. Exocytosis: In the same way that material can enter the cell through membrane vesicles and vesicle formation, the membrane of a vesicle can join with cell membrane, enabling its components to be expelled into the external medium. Exocytosis is taking place here.

Do all cells have a rigid plasma membrane?

While some cells have a flexible cell membrane, others have a stiff wall that limits their shape (and no rigid cell wall). The functions of cells are also influenced by their size.

Ex:

Plasma membrane models

  • The membrane theory of Gorter and Grendel (1920)

Evert Gorter and François Grendel, two Dutch physiologists, spoke about the discovery that led to our current understanding of the plasma membrane’s structure as a lipid bilayer. They basically assumed that, if the cell membrane is a bilayer, the experimentally determined area of the lipid monolayer would be twice as large as the surface area of the plasma membrane.

  • The Davson and Danielli model with backup from Robertson (1940–1960)

Hugh Davson, a physiologist, and James Danielli, a biologist, proposed that membranes do contain proteins. They claimed that the existence of these “membrane proteins” provided an explanation for the questions that the Gorter-Grendel model was unable to address.

  • Singer and Nicolson’s fluid mosaic model (1972)

Based on how they are connected to the lipid bilayer, the model divides membrane proteins into three classes:

Integral proteins: These proteins are completely entangled in the bilayer and are kept there by their affinity for the hydrophobic tails of the phospholipids that make up the layer’s interior.

Peripheral proteins are more hydrophilic and thus non-covalently connected to other hydrophilic regions of other membrane proteins and the polar heads of phospholipids on the membrane’s surface.

Lipid anchored proteins are covalently connected to lipid molecules that are embedded in the layer and are essentially hydrophilic, therefore they are also found on the membrane’s surface.

  • Henderson and Unwin’s membrane theory

By using the method on tilted specimens and the hypotheses put forward by DeRosier and Klug for the combination of such two-dimensional views, they were able to produce a 3D map of the cell membrane with a 7-resolution. The map displays the positions of the protein and lipid subunits as well as the locations of the polypeptide chains within each protein molecule and the connections between them in the lattice.

Is plant cell membrane rigid or flexible?

All living things, including plants, have cell membranes. In animals, it is the cell’s outermost layer and contains additional cellular organelles. Unlike the cell wall, the cell membrane is flexible and can change form as needed.

Is bacteria cell membrane rigid or flexible?

Peptidoglycan, often known as murein, makes up the majority of the bacterial cell wall. Only seen in prokaryotes, this hard peptidoglycan structure gives the cell its form and encloses the cytoplasmic membrane.

Is fungi cell membrane rigid or flexible?

It is thought that the cell membrane gives the fungal cell structural rigidity in a similar way as cell membranes provide bacteria’s cells rigidity. Sterols, glycerophospholipids, and sphingolipids make up the majority of the fungal cell membrane.

Ex:

  • While sphingolipids have a N-acylated phytosphingosine backbone known as ceramide, glycerophospholipids are made up of glycerol-3-phosphate, which contains two fatty acyl chains along with different substituents including choline, serine, and ethanolamine.
  • Phospholipids such as phosphatidic acid, phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylglycerol (PG), phosphatidylinositol (PI), cardiolipin, and sphingolipids such as inositol phosphate ceramide have been found in Saccharomyces cerevisiae
  • Sterols are amphipathic lipids with rigid and compact ring structures, sometimes known as steroid alcohols. Ergosterol often serves as the primary component of fungal cell membranes as opposed to cholesterol, which is the predominant sterol found in animal cells.

Can cell walls be semi rigid?

Essentially, a cell wall can be thought of as a thick, semi-rigid protective barrier that surrounds the cell membrane in some types of cells to protect it and determine the shape of the cell. The rigidity or strength needed cannot be provided by the cell membrane alone.

Can cell walls be flexible?

Yes. Cell walls may have a flexible character. The components of the cell wall that are present in different species vary as well.

Though typically hard, the cell wall can occasionally be found to be flexible. The species’ cell membranes are observed to be flexible.

One claims that the cell wall is a structural and functional component. The cell wall serves as a foundation for the cell. It protects cells from the hostile environment outside and also keeps their size and structure consistent.

Ex: For instance, fungi have flexible cell walls. Additionally, fungi cells have a component that gives their cell wall flexibility. Chitin, alpha-glycan, glycoproteins, and a few additional pigments make up the entire component.

Conclusion

In the above article, we studied about cell membrane rigidity and flexibility, causes for it. Rigidity of plant and bacterial cell membranes.

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