BIOL1121 UNIT3 Written Assignment : The Structure of Plasma Membrane and Molecule Transportation

 

 

 

Written Assingment Requirements

Membranes are essential components of all cells.
Briefly describe the structure of a eukaryotic plasma membrane, identifying at least two component macromolecules and describing what their basic function is within the membrane.
　

The plasma membrane protects the integrity of the interior of the cell by allowing certain substances in, while keeping other substances out.
Summarize the manner in which small molecules are permitted to pass through the membrane ensuring you explain the difference between passive, facilitated, active, and coupled transport by comparing and contrasting them.
Finally, explain the difference between endocytosis and exocytosis and provide an example of a molecule (remembering to state its function) that is transferred using this method.

 

 

 

 

 

 

The eukaryotic plasma membrane has a fluid-mosaic model and consists of a phospholipid bilayer with embedded proteins that separate the cell's internal contents from its surrounding environment. It controls the passage of organic molecules, ions, water, and oxygen into and out of the cell (Clark et al., 2020).

 

"Phosphatidylcholine constitutes a major portion of cellular phospholipids and displays unique molecular species in different cell types and tissues" (Cui & Houweling, 2002, para.1). The overall phospholipid molecule has a head area (the phosphate-containing group), which has a polar character or negative charge, and a tail area (the fatty acids), and the head can form hydrogen bonds, but the tail cannot (Clark et al., 2020). Consequently, phospholipid molecules display both hydrophilic and hydrophobic properties. The integral protein interacts with the outside of the cell, with the membrane's hydrophobic core, and with the interior of the cell, the cytosol; consequently, it supports ion transport selectively, such as nutrients, amino acids, etc. (Clark et al., 2020).

 

Passive transport

Passive transport is caused by the system in which molecules move from an area of higher concentration to an area of lower concentration, and it does not require the cell to exert any of its energy to accomplish the movement (Clark et al., 2020).

 

Facilitated transport

Facilitated transport is caused by polar molecule ions that the cell membrane's hydrophobic parts repel, and it diffuses substances into the cell without expending cellular energy with the help of membrane proteins (Clark et al., 2020).

 

Active transport

Active transport moves molecules against the concentration gradient low to high and it requires the cell's energy, usually in the form of adenosine triphosphate. Some active transport mechanisms move small-molecular weight materials, such as ions, through the membrane (Clark et al., 2020).

 

Coupled transport

Coupled transport uses the kinetic energy of sodium ions generated as the sodium ions will move down its concentration gradient across the membrane and bring, and many amino acids, as well as glucose, enter a cell this way (Clark et al., 2020).

 

 

Endocytosis is a type of active transport that moves particles, such as large molecules, parts of cells, and even whole cells, into a cell; the cell's plasma membrane causes it invaginates, forming a pocket around the target particle and transport molecules into cells (Clark et al., 2020). There are three mechanisms of endocytosis in the cell; pinocytosis, phagocytosis, receptor-mediated endocytosis.

 

Exocytosis is the process by which a vesicle moves from the cytoplasm to the plasma membrane, and it is mainly used when excreting waste materials generated inside cells to the outside of cells (Clark et al., 2020). Waste material is enveloped in a membrane and fuses with the plasma membrane's interior, and the waste material expels into the extracellular space when the membranous envelope on the cell's exterior opens (Clark et al., 2020). There are two mechanisms of exocytosis; the constitutive and the regulated secretory.

 

 

 

 

 

References

 

Clark, M.A., Choi, J. & Douglas, M. (2020). Biology 2e. Open Stax. Retrieved from https://openstax.org/books/biology-2e/pages/preface 

 

Cui, Z., & Houweling, M. (2002). Phosphatidylcholine and cell death. Biochimica et Biophysica Acta (BBA)-Molecular and Cell Biology of Lipids, 1585(2-3), 87-96.Retrieved from https://www.sciencedirect.com/science/article/abs/pii/S1388198102003281