There Is No Such a Thing as a Typical Cell

There Is No Such a Thing as a Typical Cell

Introduction

Every human body begins as a single cell, or zygote, formed when the father's sperm and mother's egg join. The zygote divides to give rise to two cells that are virtually identical to each other. These two daughter cells can each divide to give rise to four cells, which can then, in turn, divide again. This process allows for an exponential increase in cell number as each round of cell division can potentially double the number of cells produced by the former division. This mechanism involving exponential cell division can be repeated as many times as required to yield enough cells to build a human (Elowitz et al. 2002).

A typical cell contains ~1-2 pg of mRNA, which translates to a few hundred thousand molecules transcribed from gDNA. The high sensitivity of reverse transcription (RT) combined with quantitative real-time PCR (qPCR) makes possible to reproducibly and reliably detect gene expression signatures at the level of a single cell. Although there has been increased interest in single-cell profiling, there are no standard tools for this emerging application (Rogers 1983).

There are a number of different kinds of human cells, such as skin, muscle, and nerve cells. These cells have many elements in common, but they also have many unique elements. It is the elements that are specific to each cell type that result in the differentiated appearance and function of the specialized cells.

Discussion

The elements that are ordinary to most human cells are also common to many types of cells in other animals. For example, there are certain activities, such as obtaining nutrients and converting them into cell components and usable energy, which all cells must perform to be alive. Furthermore, most cells, regardless of their type, use similar mechanisms to perform such functions. Cell biologists refer to these types of mechanisms as housekeeping functions. This degree of commonality further legitimizes the use of model organisms for insights into human biology. Of further interest is the observation that cells that perform similar functions in different organisms are also remarkably similar structurally. For some cell types, it is impossible to tell the difference between a cell from a human, a mouse, or a fish simply by looking at it under a microscope (Beyer et al. 2009).

A typical animal cell can be compared to a factory containing different kinds of machinery. The outer boundary of an animal cell is called the plasma membrane. This membrane separates the material inside the cell from the external environment, much like our skin or the walls of a factory building. Within the cell are many small structures, called organelles, which carry out the cell's life activities. An organelle, or "little organ," is a cellular component that has a structure and function, much like the organs in an animal. Most organelles are surrounded by a membrane that is similar in typical composition, if not identical, to the plasma membrane surrounding the ...