Membrane Surface Area

The plasma membrane, which covers the outside of the cell, is known as the surface area. The volume of a cell is the amount of space it contains. The surface area divided by the volume is the ratio. This shows how much surface area is accessible about the cell’s size.

Regulation Of Cell Surface Area

The wonderfully choreographed regulation of cell shape and volume is a fundamental theme in cell biology and physiology. Cell surface area regulation is also a specific duty for cells, albeit it is less well known. Maintaining a sufficient surface area is not an unintended consequence of volume regulation or shape modification. 

On the other hand, these enucleate cells are outliers because they lack an endomembrane. Endomembrane is used by most cells to constantly rework their plasma membrane while preserving their size and form. 

The targeting and output of proteins and the delivery of vesicle contents are all heavily investigated aspects of membrane traffic. Our main goals are to emphasise SAR as a distinct cellular process and gather evidence to support the notion that membrane tension is critical to the task. 

Cells can’t “measure” their volume or SA directly, yet they must regulate both. We suggest a homeostatic link between plasma membrane tension and plasma membrane area, implying that cells monitor and respond to changes in membrane tension set points. 

In the context of SAR, we look at how membrane strength is maintained during membrane turnover, which is a little-studied aspect of SA dynamics. The review reveals that the latter continues to do innovative work on tension-sensitive SAR, but it is primarily focused on animal cells. 

A Structure That Increases the Surface Area Of The Membrane

A cell membrane’s primary function is to receive nutrients from the surrounding environment.

To accomplish this, proteins in the cell membrane must recognise the presence of molecules that should be absorbed into the cell. A cell can improve its ability to identify essential chemicals in two ways. One way is to have more protein receptors that recognise the chemical on the surface membrane. 

The alternative option is to have a wider membrane region where these protein receptors can be placed. This second technique, having a more extensive membrane surface area, also allows a molecule to pass across multiple membranes.

Surface Area (Volume Ratio)

The volume of a cell expands faster than its surface area, resulting in a lower Surface area: Volume ratio. As a result, expanding cells tend to divide and remain tiny to maintain a high SA: Vol ratio optimal for survival.

Raising the SA: Volume Ratio

To improve material transfer, cells and tissues that specialise in material exchanges or gas also increase surface area. 

• Intestinal tissue in the digestive tract can form ruffled structures called villi. These villi increase the surface area of the inner lining. 
• Alveoli in the lungs have microvilli, which are membranous extensions whose function is to increase the surface area of the total membrane.

Microvilli Structure

Microvilli are tiny projections that protrude from a cell’s surface. Multiple microvilli can be found near one another, resembling many fingers extending from a cell. A microvillus has a height of one micrometre and a width of 0.1 micrometres. Long actin filaments line the inside of a microvillus. Actin filaments are a component of the cell’s internal skeleton. In this scenario, the internal skeleton takes the form of a finger, with a bundle of rods poking into and extending the cell membrane.

Microvilli and Their Function

Microvilli’s primary function is to increase the area of a cell’s membrane through which nutrients can be absorbed. The nutrients in digested food are absorbed into the intestines’ cells. 

Microvilli can number up to 1,000 in an epithelial cell in the intestines. Microvilli boost a cell’s surface area by 25 times. The microvilli also produce enzymes that break down proteins and carbohydrates into smaller, easier-to-absorb particles. Motor proteins pull the actin rods within a microvillus. The microvilli move due to the motor proteins pushing on them, causing a stirring action in the liquid surrounding them.

Non-Motile Cilia Structure

Non-motile cilia are structures that increase the surface area of a cell membrane. Cilia that are not motile exert force on the cell membrane like oars. They are more elongated and thinner than microvilli. Primary cilia are non-motile cilia, i.e. that do not move. They vary from motile cilia, which can move by beating back and forth like an oar, in that they cannot move by pounding back and forth. A primary cilium is similar to a motile cilium in structure, but it lacks the central column and motor protons that drive the cilium to bend.

Non-Motile Cilia and Their Function

A primary cilium, also known as a non-motile cilium, detects the presence of chemicals. Primary cilia, like microvilli, push into and expand the cell membrane like a finger, increasing the surface on which an excellent chemical receptor can be positioned. It also expands the area where protein channels that allow nutrients to enter the cell can be found. 

Non-motile cilia have proteins on their surfaces to convey messages to the cell’s command centre. Non-motile cilia function similarly to microvilli in that they aid the cell’s ability to identify substances in the environment.

Surface Area Division and Regulation

Two concepts for membrane supply to permit cell division include exocytosis of intracellular vesicles and unfolding tiny surface membrane reservoirs or wrinkles. We examined the entire cell surface area of proliferating Dictyostelium cells, flattened by an agar overlay, which removed the intricacy of unfolding surface membrane reservoirs. Membrane’s surface reservoirs’ unfolding was not necessary for cell division. The overall cell surface area fell significantly from interphase to metaphase under the agar overlay, then grew by roughly 20% during cytokinesis. 

The differences in cell surface area could be due to an imbalance of endocytosis and exocytosis. Clathrin-dependent endocytosis was also significantly reduced during cytokinesis, although it did not contribute significantly to the regulation of cell surface area, contrary to previous studies in cultured animal cells. Furrowing was required for cell membrane expansion during cytokinesis and vice versa.

Conclusion

The plasma membrane is the area on the outside of the cell that is referred to as surface area. The volume of a cell is the amount of space it contains. The surface area divided by the volume is the ratio. This shows how much surface area is accessible in relation to the cell’s size.