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Prokaryotic and Eukaryotic
Cells
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Printed: January 8, 2015
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C HAPTER
Chapter 1. Prokaryotic and Eukaryotic Cells
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Prokaryotic and Eukaryotic
Cells
• Distinguish between eukaryotic and prokaryotic cells.
Are bacteria cells like our cells?
Yes and no. Bacteria cells are similar to our cells in some ways. Like our cells, bacteria cells have DNA and a
plasma membrane. But bacteria are simpler and unique in their own ways. The term prokaryote comes from the
Greek "pro" meaning "before" or "first", and "karyon" meaning "nut" or "kernal". These are the first cells to appear
in the fossil record - over three and half billion years ago. It took another two billion years for complicated cells
like our own to evolve. Let’s take a look at the two types of cells that all living things on Earth are made of.
Prokaryotic and Eukaryotic
There are two basic types of cells, prokaryotic cells and eukaryotic cells. The main difference between eukaryotic
and prokaryotic cells is that eukaryotic cells have a nucleus. The nucleus is where cells store their DNA, which is
the genetic material. The nucleus is surrounded by a membrane. The nuclear-membrane is very similar to the cell
membrane - evidence that this membrane evolved from a modified cell membrane sometime between 3.6 billion and
1.5 billion years ago. Organisms with eukaryotic cells are called eukaryotes. Animals, plants, fungi, and protists
are eukaryotes. All multi-cellular organisms are eukaryotes. Eukaryotes may also be single-celled.
Prokaryotic cells do not have a nucleus. Instead, their DNA floats around inside the cell. Organisms with prokaryotic
cells are called prokaryotes. All prokaryotes are single-celled organisms. Bacteria and Archaea are the two groups
of prokaryotes. Archaea were orginally classified as bacteria or "archaeabacteria", but recent evidence has led
scientists to give them their own distinct grouping: genes more closely related to eukaryotes, distinct biochemical
processes, etc. Archaea are common extremophiles in hotsprings, in the oceans, and in a wide range of terrestrial
habitats.
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FIGURE 1.1
Fossilized stromatolites from Shark Bay,
Australia. These are some of the oldest
fossils found on Earth - dating back 3.6
billion years. The layers are formed from
successive layers of ancient prokaryotic
bacteria.
Both prokaryotic and eukaryotic cells have structures in common. All cells have a plasma membrane, ribosomes,
cytoplasm, and DNA. The plasma membrane, or cell membrane, is the phospholipid layer that surrounds the cell
and protects it from the outside environment. Ribosomes are found in all cells, both prokaryote and eukaryote, and
are relatively small, non-membrane bound organelles where proteins are made (a process called protein synthesis).
The cytoplasm is all the contents of the cell inside the cell membrane, not including the nucleus. It is about 80%
water, salts, and other organic compounds (carbs, amino acids, proteins, lipids).
Eukaryotic Cells
Eukaryotic cells usually have multiple chromosomes, composed of DNA and protein. Some eukaryotic species have
just a few chromosomes, others have close to 100 or more. These chromosomes are protected within the nucleus.
In addition to a nucleus, eukaryotic cells include other membrane-bound structures called organelles. Organelles
allow eukaryotic cells to be more specialized than prokaryotic cells. Pictured below are the organelles of eukaryotic
cells ( Figure below), including the mitochondria, endoplasmic reticulum, and Golgi apparatus. These will be
discussed in additional concepts.
Prokaryotic Cells
Prokaryotic cells ( Figure 1.3) are usually smaller and simpler than eukaryotic cells. They do not have a nucleus
or other membrane-bound organelles. In prokaryotic cells, the DNA, or genetic material, forms a single large circle
that coils up on itself. The DNA is located in the main part of the cell.
TABLE 1.1: Comparison of Prokaryotic and Eukaryotic Cells
Feature
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Prokaryotic cells
Eukaryotic cells
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Chapter 1. Prokaryotic and Eukaryotic Cells
TABLE 1.1: (continued)
Feature
Nucleus
DNA
Membrane-enclosed organelles
Examples
Prokaryotic cells
No
Single circular piece of DNA
No
Bacteria
Eukaryotic cells
Yes
Multiple chromosomes
Yes
Plants, animals, fungi
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FIGURE 1.2
Eukaryotic cells have many specialized
features. Organelles are parts of the cell
that enclosed in their own membrane and
have specific jobs. The nucleus of a eukaryotic cell is the largest organelle - enclosing the cell’s DNA is a special double
-lipid membrane (nuclear membrane).
FIGURE 1.3
Prokaryotes do not have a nucleus. Instead, their genetic material is located in
the main part of the cell.
Vocabulary
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•
•
•
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•
•
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•
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cytoplasm: Entire contents of the cell inside the plasma membrane, excluding the nucleus.
deoxyribonucleic acid (DNA): Nucleic acid that is the genetic material of all organisms.
endoplasmic reticulum: Organelle that is the site of lipid synthesis and protein modification.
eukaryote: Organism with cells containing a nucleus and membrane-bound organelles.
eukaryotic cell: Cell that contains a nucleus and membrane-bound organelles.
Golgi apparatus: Organelle that processes and packages proteins.
mitochondrion (plural mitochondria): Organelle of the cell in which energy is generated.
nucleus: Cell structure that contains the genetic material, DNA.
organelle: Structure within the cell that has a specific role.
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•
•
•
•
Chapter 1. Prokaryotic and Eukaryotic Cells
plasma membrane: The lipid barrier that surrounds the cell; known as the cell membrane.
prokaryote: Organism that lacks a nucleus; i.e. bacteria.
prokaryotic cell: Cell without a nucleus or membrane-bound organelles.
ribosome: Organelle in which proteins are made (protein synthesis).
Summary
• All cells have a plasma membrane, ribosomes, cytoplasm, and DNA.
• Prokaryotic cells lack a nucleus and membrane-bound structures.
• Eukaryotic cells have a nucleus and membrane-bound structures called organelles.
Practice
Use the resource below to answer the questions that follow.
• Compare Prokaryotic and Eukaryotic Cells at http://www.youtube.com/watch?v=QON4z9vo7Ag (1:55)
MEDIA
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/57353
1. What does "naked" DNA mean? What kinds of organisms have "naked" DNA?
2. Where do you find membrane bound organelles? Are plasmids membrane bound organelles?
3. What is the size of mitochondria in prokaryotes?
• Quizzes on Prokaryotic or Eukaryotic by neoK12 at http://www.neok12.com/quiz/CELSTR03 and http
://www.neok12.com/quiz/CELSTR04
Review
1.
2.
3.
4.
What do all cells have in common?
What are organelles?
Compare the location of the genetic material of eukaryotic cells and prokaryotic cells.
What are some examples of eukaryotes?
References
1. Mariana Ruiz Villarreal (LadyofHats), modified by CK-12 Foundation. . Public Domain
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