Prokaryotes Vs. Eukaryotes: What Are the Differences?

Comparing the Two Basic Types of Cells

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Escherichia coli, also known as E. Coli, is the most extensively studied prokaryotic organism. Photo © Ian Cuming / Getty Images.

All living organisms can be sorted into one of two groups depending on the fundamental structure of their cells. These two groups are the prokaryotes and the eukaryotes. Prokaryotes are organisms made up of cells that lack a cell nucleus or any membrane-encased organelles. Eukaryotes are organisms made up of cells that possess a membrane-bound nucleus (that holds genetic material) as well as membrane-bound organelles.

The cell is a fundamental component of our modern definition of life and living things. Cells are regarded as the basic building blocks of life and are used in the elusive definition of what it means to be 'alive'.

Let's take a look at one definition of life:

"Living things are chemical organizations composed of cells and capable of reproducing themselves." ~ from Biological Science by William T. Keeton

This definition is rooted in two theories, cell theory and biogenesis theory. Cell theory, first proposed in the late 1830s by two German scientists Matthias Jakob Schleiden and Theodor Schwann, states that all living things are composed of cells. Biogenesis theory, proposed in 1858 by Rudolf Virchow states that all living cells arise from existing (living) cells and no cells are created spontaneously from non-living matter.

Cells organize things. They keep chemical processes tidy and compartmentalized so individual cell processes do not interfere with others and the cell can go about its business of metabolizing, reproducing, etc.

To organize things, cell components are enclosed in a membrane which serves as a barrier between the outside world and the cell's internal chemistry. The cell membrane is a selective barrier, meaning that it lets some chemicals in and others out and in doing so maintains the balance necessary for the cell to live.

The cell membrane regulates the crossing of chemicals in and out of the cell in several ways: by diffusion (the tendency of solute molecules to minimize concentration and thus move from an area of higher concentration towards an area of lower concentration until concentrations equalize), osmosis (the movement of solvent across a selective boundary in order to equalize the concentration of a solute that is unable to move across the boundary), and selective transport (via membrane channels and membrane pumps).

Prokaryotes

Prokaryotes are organisms made up of cells that lack a cell nucleus or any membrane-encased organelles. This means the genetic material DNA in prokaryotes is not bound within a nucleus. Additionally, the DNA is less structured in prokaryotes than in eukaryotes. In prokaryotes, DNA is a single loop. In Eukaryotes, DNA is organized into chromosomes. Most prokaryotes are made up of just a single cell (unicellular) but there are a few that are made of collections of cells (multicellular). Scientists have divided the prokaryotes into two groups, the Bacteria and the Archaea.

A typical prokaryotic cell might contain the following parts:

  • cell wall
  • plasma membrane
  • cytoplasm
  • flagella and pili
  • nucleoid
  • plasmid

Eukaryotes

Eukaryotes are organisms made up of cells that possess a membrane-bound nucleus (that holds genetic material) as well as membrane-bound organelles. Genetic material in eukaryotes is contained within a nucleus within the cell and DNA is organized into chromosomes. Eukaryotic organisms may be multicellular or single-celled organisms. All animals are eukaryotes. Other eukaryotes include plants, fungi, and protists.

A typical eukaryotic cell might contain the following parts:

  • plasma membrane
  • nucleolus
  • nucleus
  • chromosomes
  • rhibosome
  • vesicle
  • endoplasmic reticulum
  • Golgi apparatus
  • cytoskeleton
  • cytoplasm
  • lysosome
  • centrioles
  • mitochondria
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Klappenbach, Laura. "Prokaryotes Vs. Eukaryotes: What Are the Differences?" ThoughtCo, Mar. 20, 2017, thoughtco.com/what-are-prokaryotes-and-eukaryotes-129478. Klappenbach, Laura. (2017, March 20). Prokaryotes Vs. Eukaryotes: What Are the Differences? Retrieved from https://www.thoughtco.com/what-are-prokaryotes-and-eukaryotes-129478 Klappenbach, Laura. "Prokaryotes Vs. Eukaryotes: What Are the Differences?" ThoughtCo. https://www.thoughtco.com/what-are-prokaryotes-and-eukaryotes-129478 (accessed October 21, 2017).