Comparing Prokaryote and Eukaryote Cells
Understanding Differences in Cell Structure
By Laura Klappenbach, About.com Guide
All living organisms can be sorted into one of two groups depending on the structure of their
cells. These two groups are the prokaryotes and the eukaryotes.
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.
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.
Eukaryotes grow and reproduce through a process called mitosis. In organisms that also
reproduce sexually, the reproductive cells are produced by a type of cell division called meiosis.
Most prokaryotes reproduce through a process called binary fission. During binary fission, the
single DNA molecule replicates and the original cell is divided into two identical daughter cells.
Both eukaryotic and prokaryotic organisms get the energy they need to grow and maintain
normal cellular function through cellular respiration. Cellular respiration has three main stages:
glycolysis, the citric acid cycle, and electron transport. In eukaryotes, most cellular respiration
reactions take place within the mitochondria. In prokaryotes, they occur in the cytoplasm and/or
within the cell membrane.
The Anatomy of a Cell
An Inside Look at Living Cells and Their Building Blocks
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. (Keeton 1986, 85)"
Cell Function
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.
Two Fundamental Cell Types
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.
Anatomy of a Prokaryotic Cell
A typical prokaryotic cell might contain the
following parts:
 cell wall
 plasma membrane
 cytoplasm
 flagella and pili
 nucleoid
 plasmid
Anatomy of a Eukaryotic Cell
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
The Cell Membrane
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).