Plasma Membrane: Structure, Function, and Transport -Bioscience 365

This report provides an overview of the plasma membrane, emphasizing its structure and function in separating intracellular and extracellular fluids. It discusses the lipid bilayer composed of phospholipids, cholesterol, and proteins, highlighting the amphipathic nature of phospholipids and the roles of integral and peripheral proteins. The report explains how cholesterol maintains membrane structure and how carbohydrates facilitate cell recognition. Furthermore, it elaborates on the transport mechanisms across the membrane, including simple diffusion of oxygen and facilitated diffusion of sodium ions through channel proteins. The function of the Na+/K+ ATPase pump in maintaining ion gradients is also discussed. The report references relevant academic sources to support its explanations, offering a comprehensive understanding of the plasma membrane's critical role in cellular biology. Desklib provides access to similar solved assignments and study tools for students.

Running head: APPLIED BIOSCIENCE 365
Assessment 2- Part A
Name of the Student
Name of the University
Author Note

1APPLIED BIOSCIENCE 365
The plasma membrane defines boundary of a cell and separates it into two primary fluid
compartments namely, intracellular fluid inside cells and extracellular fluid outside cells. It is
made up of lipid bilayer that forms the basic structure of the membrane, and is largely composed
of phospholipids, with traces of cholesterol, glycolipids, and lipid rafts. A phospholipid
molecule contains a hydrophilic phosphate group/head on one end, and hydrophobic chains of
fatty acids that make up the tails. The lipid tails are composed of saturated or unsaturated fatty
acids. Owing to the fact that the phospholipids contain both hydrophilic and hydrophobic
regions, the lipid bilayer is termed as amphipathic (Ingólfsson et al., 2014). However, most often
it gets interrupted by several proteins. Two proteins commonly related to the plasma membrane
are namely, integral/intrinsic or extrinsic/peripheral proteins. The integral proteins are found to
remain embedded in the plasma membrane. Peripheral proteins are located on the outer or inner
surface of the bilayer. However, they are also found attached to the surfaces of the integral
proteins.
Figure 1- Plasma membrane structure
Source- (Nicolson, 2014)

2APPLIED BIOSCIENCE 365
Owing to the rigid ring structures, cholesterol is found to play an essential role in
maintaining structure of the membrane. It creates a difference on fluidity of the membrane by
interfering with movement of the fatty acid chain and lowering fluidity, at high temperatures.
Carbohydrates (glycoproteins) are also present in the plasma membrane and play an essential
role in cell-to-cell recognition (Nicolson, 2014). Several substances such as, oxygen and carbon
dioxide gases are found to easily diffuse through phospholipid bilayer. Oxygen is present in high
concentration outside the cells. The structure of phospholipid bilayer creates provisons for the
uncharged, small oxygen molecules to pass through the plasma membrane, by the process of
simple diffusion, to the region of their lower concentration. Thus, oxygen moves down its
concentration gradient, without expenditure of energy (Stein, 2012).
On the other hand, the process of facilitated diffusion brings about movement of sodium
ions, with the assistance of special channel proteins. Na+ ions are concentrated outside the cells,
and cannot pass through the bilayer due to their charge. Membrane proteins form Na+
pores/channels and help the ions move along the concentration gradient to the interior. This kind
of diffusion is a passive process. Hence, there is no energy expenditure by the cell. In addition,
the Na+/K+ ATPase pump helps in transporting out Na+ of a cell while facilitating movement of
K+ inside the cells (Stein, 2012). Thus, the lipid bilayer is found to form the foundation of the
plasma membrane.

3APPLIED BIOSCIENCE 365
References
Ingólfsson, H. I., Melo, M. N., Van Eerden, F. J., Arnarez, C., Lopez, C. A., Wassenaar, T. A., ...
& Marrink, S. J. (2014). Lipid organization of the plasma membrane. Journal of the
american chemical society, 136(41), 14554-14559. DOI: 10.1021/ja507832e
Nicolson, G. L. (2014). The Fluid—Mosaic Model of Membrane Structure: Still relevant to
understanding the structure, function and dynamics of biological membranes after more
than 40years. Biochimica et Biophysica Acta (BBA)-Biomembranes, 1838(6), 1451-1466.
https://doi.org/10.1016/j.bbamem.2013.10.019
Stein, W. (2012). The movement of molecules across cell membranes (Vol. 6). Elsevier, 126-176.
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