Prokaryotes Vs. Eukaryotes | Difference Between Cells & Examples

Written by

Malcolm McKinsey

January 12, 2023

Fact-checked by

Paul Mazzola

Prokaryotic and eukaryotic cells

Eukaryotic cells contain a nucleus and organelles bound by plasma membranes. Fungi, plants, and animals are made of eukaryotic cells (eukaryotes). Prokaryotic cells do not have a membrane-bound nucleus or organelles. All bacteria and members of Archaea are made of prokaryotic cells (prokaryotes).

Difference between eukaryotic and prokaryotic cells

The most obvious difference between them is that prokaryotes have no nuclei, but there are four major differences between a eukaryotic and prokaryotic cell:

1. No prokaryotic cell has a nucleus; every eukaryotic cell has a nucleus.

2. Prokaryotic cells have no mitochondria; nearly every eukaryotic cell has mitochondria.

3. Prokaryotic cells have no organelles enclosed in plasma membranes; every eukaryotic cell has a nucleus and organelles, each enclosed in plasma membranes.

4. Prokaryotic cells have circular strands of DNA; eukaryotic cells have multiple molecules of double-stranded, linear DNA.

Similarities between prokaryotic and eukaryotic cells

For all their differences, prokaryotes and eukaryotes have a few similarities share some common structures (due to physics and evolution), and though their DNA is different, they even share some genetic features.

Both types of cells have five similarities:

1. Both types of cells carry on all the necessary functions of life (adaptation through evolution, cellular organization, growth and development, heredity, homeostasis, reproduction, metabolism, and response to stimuli). However, they do these things in different ways.

2. Both cells carry DNA and rDNA (ribosomal DNA)

3. Both prokaryotic cells and eukaryotic cells have vesicles.

4. Both prokaryotes and eukaryotes may be single-celled organisms. Amoebas, paramecia, and yeast are all single-cell eukaryotes.

5. Both types of cells have vacuoles, storage units for food and liquid.

Structures found in prokaryotic and eukaryotic cells

All living organisms use cellular organization to create structures to conduct life processes. Cells organize into tissues, which organize into organs, which organize into amazing life forms like plants, fungi, dogs, ducks, and people.

Intracellular structures are common to both types of cells. Both prokaryotic and eukaryotic cells have:

• DNA

• Ribosomes

• Cytoplasm

• Plasma membrane

Prokaryotes

An organism with prokaryotic cells is a prokaryote. Prokaryotic organisms get their names from the Greek roots, pro (before) and karyon (nut or kernel). This roughly means they are cells with structures so simple that they came from a time before a cell's nucleus existed.

The three domains of life, Eukaryota, Bacteria, and Archaea, include two branches that are prokaryotes:

1. Bacteria – The first prokaryotes were discovered in 1676. Bacteria have bacterial rRNA (Ribosomal RNA), no nuclear membrane, and cell membranes composed primarily of diacylglycerol diester lipids (ester-linked lipids).

2. Archaea – Single-cell organisms. They have no nuclear membrane and share some qualities with bacteria (rDNA, circular chromosomes, asexual reproduction) but are set apart from bacteria by their unique rDNA and ether-linked lipids in their cell membranes.

Only the domain, Eukaryota, has eukaryotic cells.

Prokaryotic cells

Prokaryotic cells are extremely small, much smaller than eukaryotic cells. A typical prokaryotic cell is of a size ranging from 0.1 microns (mycoplasma bacteria) to 5.0 microns.

1 micron or micrometer, $\mu m$, is one-thousandth of a millimeter or one-millionth of a meter.

Anywhere from 200 to 10,000 prokaryotic cells could fit on the head of a pin.

Their small size makes prokaryotic cells just one-half to one-thousandth the size of a eukaryotic cell, which is typically between 10 and 100 microns.

One amazing prokaryotic outlier is Thiomargarita namibiensis, the largest bacterium ever discovered, coming in at a whopping 100 to 300 microns. That is large enough to see in a light microscope.

Prokaryotic Organelles

Prokaryotes have no organelles in their cells! All the equivalent functions of eukaryotic cells are performed by four structures: a plasma membrane, cytoplasm, ribosomes, and genetic material (both rDNA and DNA).

Facts about prokaryotic cells

1. Prokaryotes help recycle nutrients by decomposing dead organisms.

2. Bacteria in the intestines and mouths of all higher animals help with the digestion of food.

3. The DNA of a prokaryotic cell is tightly coiled in a ‘nucleoid,’ which is not a true nucleus since it has no membrane.

4. Prokaryotic rDNA is a single ring of DNA and is only about 0.1 percent of the amount of DNA in a eukaryotic cell.

5. Prokaryotic cells have many more ways to obtain and use energy than eukaryotic cells, performing photosynthesis, respiration in common with eukaryotes but also using nitrogen fixation, denitrification, sulfate reduction, and methanogenesis.

6. Roughly half of all bacteria have flagella, little whip-like external structures that all them to move.

7. Prokaryotic cells can use pili and fimbriae; also types of external growths, to stick to other cells or surfaces they make their home.

8. Prokaryotic cells can perform binary fission roughly every 24 hours, meaning they can reproduce exponentially fast.

9. All adult humans have about 0.2 kg of bacteria in their digestive systems and on their skin; recent studies put the number of bacteria in our bodies as just about equal to the number of eukaryotic cells.

10. Prokaryotic cells are the oldest life forms on earth, dating back 3.5 million years.

Eukaryotes

Fungi, plants, protista, and all animals (including humans) are eukaryotes. We are all built with eukaryotic cells. The word eukaryote comes from two Greek roots, eu (good, well), and karyon (nut, kernel), so a eukaryote has a well-defined or “good” nucleus (kernel) in its cells.

Eukaryotes cells

Eukaryotic cells have nuclei and organelles, which sets them apart from prokaryotic cells.

The organelles in eukaryotic cells act as tiny membrane-bound compartments performing all the functions of life in the cell: energy acquisition and transfer, digestion, waste management, reproduction, and cellular respiration.

Some of these eukaryotic cell organelles are:

• Mitochondria (cell powerhouses)

• Chloroplasts (in plants and some algae, for photosynthesis)

• Endoplasmic reticulum (the cell transport system)

• Golgi apparatus (protein packagers)

• Ribosomes (protein synthesis)

• Vacuoles (water and food storage)

• Lysosomes (digestive processes)

• Peroxisomes (metabolic processes)

• Nucleus (the mind and brain of the cell)

Size of eukaryotic cells

In general, eukaryotic cells are much bigger than prokaryotic cells. One eukaryotic cell could be double to 1,000 times the size of a prokaryotic cell. Eukaryotic cells measure between 10 and 100 microns, which means you could barely see them with a standard school light microscope.

Eukaryote Characteristics

1. Eukaryotes can be single-celled organisms (like protozoa or paramecia) or multicellular organisms (like you or an elephant)

2. The largest organism on earth is a eukaryote nicknamed the Humongous Fungus, a specimen of Armillaria ostoyae that covers almost four square miles under the ground of Malheur National Forest in Oregon.

3. Eukaryotes have linear chromosomes, contrasting with the single ring of rDNA in prokaryotes.

4. Eukaryotes include animal and plant cells, differentiated in many ways but most obviously by the plasma membrane of animal cells and synthesis cell walls in plants.

5. Eukaryotic cells store chromatin (DNA and proteins) in a gel-like fluid called the nucleoplasm inside the nucleus.

6. Mitochondria, found only in eukaryotic cells, have their own DNA chromosome, which may indicate they were once freely existing, independent prokaryotic cells “captured” by eukaryotic cells.

7. In contrast with the mind-blowing miniature prokaryotic cells, eukaryotic cells are so large, even some of their organelles are visible under the light microscope of a high school science laboratory.

8. The oldest eukaryote, Grypania, dates back around 1.874 billion years ago; fossils of this eukaryote were discovered in a Michigan iron mine.

9. Eukaryotes mostly reproduce sexually, though some do use cell division.

10. Adult humans have around $3\cdot {10}^{13}$ human (eukaryotic) cells in their bodies and a roughly equal number of bacteria (prokaryotes).

Prokaryotes and eukaryotes quiz

Cell biology can be tricky stuff, so check your understanding by answering these questions.

1. Are animal cells prokaryotic or eukaryotic?

2. Name two locations of prokaryotic cells in the human body.

3. Are mitochondria found in prokaryotic cells?

4. Name one feature of eukaryotic cells that is not found in prokaryotic cells.

5. What type of cells are prokaryotic?

6. List three similarities between prokaryotic and eukaryotic cells.

7. Do prokaryotes have organelles?

Review the reading and review your answers before you review our answers!

1. Animal cells are eukaryotic.

2. Two locations of prokaryotic cells in the human body are in the intestine (where gut bacteria help you digest food) and on your skin (where bacteria thrive).

3. Mitochondria are not found in prokaryotic cells; they are only in eukaryotic cells.

4. One feature of eukaryotic cells that is not found in prokaryotic cells is the cell nucleus.

5. Simple, primitive cells are prokaryotic; they have no nucleus and no organelles encased in plasma membranes.

6. Three similarities between prokaryotic and eukaryotic cells are that both have vesicles, vacuoles, and the ability to carry out the eight functions of life.

7. Prokaryotes do not have organelles.