Cells are the basic building block of life.
The smallest living organisms only need one of these building blocks and others only need a handful.
More complex life forms on the evolutionary tree, such as moss, saguaro cacti and black bears, are made up of millions or trillions of cells that cooperate to form an individual organism.
All of these cells, whether they operate as a solitary bacterial cell or as part of a complex system such as the human body, can be sorted into two main categories: eukaryotic cells and prokaryotic cells.
TL;DR (Too Long; Didn't Read)
Most prokaryotes are unicellular and are either archaea or bacteria. Their cells are smaller than eukaryotic cells. Eukaryotes include larger, more complex organisms such as plants and animals. Only eukaryotes have membrane-bound organelles and a nucleus. Prokaryotes divide via using binary fission, while eukaryotic cells divide via mitosis.
Eukaryotes reproduce sexually through meiosis, which allows for genetic variance.
Prokaryotic cells reproduce asexually, copying themselves. Despite this, gene transfer processes still allow for genetic variance. One of these is transduction in which viruses move DNA from one bacterium to another.
Prokaryotes vs. Eukaryotes: The Basics
All of known life on Earth is sorted into a classification system that begins with three categories called domains and spreads out with each descending rank. This is what is commonly known as the tree of life.
The three domains are:
The organisms in Archaea and Bacteria are prokaryotes, while the organisms in Eukarya have eukaryotic cells.
The Archaea domain has subcategories, but scientific sources differ on whether these categories are phyla or kingdoms. They are:
The Bacteria domain used to continue directly down the tree into the single Monera kingdom. However, newer classification systems eliminate Monera and divide the Bacteria domain into the two kingdoms of Eubacteria and Archaebacteria, which is sometimes written as Archaea but should not be confused with the domain of Archaea.
The Eukarya domain is divided into four kingdoms. These are:
All plant, protist, fungal and animal cells are eukaryotes. Most of them are multicellular, although there are some exceptions. In contrast, prokaryotes – bacteria and archaea – are single-celled organisms, with only a few exceptions. Prokaryotes tend to have smaller cell sizes than eukaryotes.
Major Differences in Cell Structure
The reason for the difference in cell sizes between prokaryotic cells and eukaryotic cells belongs to the different structure and organization between the two types of cells.
The lack of membrane-bound organelles in prokaryotes might be the most noticeable difference. While eukaryotic cells contain organelles enclosed in membranes – two examples would be the Golgi body and the endoplasmic reticulum – prokaryotes do not.
Prokaryotes also lack a membrane-bound nucleus, which is another organelle. Without a nucleus or any other organelles, prokaryotic cells are incapable of the kinds of specialized functions that eukaryotic cells engage in.
They cannot perform the advanced functions that cells with many supportive organelles can do.
Instead, most of their DNA is in one chromosome-like structure that sits in an area of the cytoplasm called the nucleoid. This nucleoid does not have a membrane of its own. Additional bits of DNA called plasmids are shaped like rings and exist in the cytoplasm outside the nucleoid.
Differences in Organization
Prokaryotic cells engage in reproduction through a process of cell division called binary fission.
Eukaryotic cells use a different process of cell division called mitosis, which involves a constant cycle of cell growth and development.
There are frequent checkpoints for the cell to go through, monitoring the cell’s external and internal conditions, and redirecting the cell’s resources and functions when necessary.
A fundamental part of all life on Earth is the transfer of genetic material to future generations.
Eukaryotes reproduce sexually through a process called meiosis, which randomly sorts the genes from two parents to form the DNA of the offspring.
Sexual reproduction maximizes the genetic variability of the offspring of two parents, strengthening the genetic line and minimizing the risk of a random mutation wiping out most of a population.
Prokaryotes reproduce asexually, which creates a precise copy of the original cell. Genetic variance comes in the form of less complex processes of gene transfer than eukaryotes, such as transduction. In this process, genes are transferred from one bacterial cell to another by means of viral cells.
The viruses grab the plasmids from one bacterium and transfer it to another bacterial cell. The DNA in the plasmid becomes integrated with the other DNA of the recipient cell.
|Prokaryotic Cell||Eukaryotic Cell|
|Membrane Bound Organelles Present||No||Yes, includes things like mitochondria, golgi body, endoplasmic reticulum, chloroplast, etc)|
|Domains||Bacteria and Archaea||Eukarya|
|Kingdoms||Eubacteria and Archaebacteria||Plantae, Fungi, Animalia, Protista|
|How DNA Is Stored||Nucleoid||Chromosomes|
|Cell Reproduction/Division||Binary fission||Mitosis (division of somatic cells) and Meiosis (creation of cells used for sexual reproduction)|
|Plasma Cell Membrane Present||Yes||Yes|
Similarities Between Prokaryotes and Eukaryotes
For all the differences between prokaryotic cells and eukaryotic cells, they have some features in common, too.
Both cells have a plasma membrane, which serves as a barrier between the inside of the cell and the outside.
The plasma membrane uses certain molecules embedded within it to allow foreign bodies to pass into the cell or to allow matter within the cell to pass out of the cell.
Proteins embedded in the membrane do something similar, as well: they act as pumps that push matter into or out of the cell, rather than allowing it to pass through.
Both prokaryotes and eukaryotes have ribosomes.
Ribosomes are small organelles used to synthesize proteins as the cell needs them. They can either float freely in the cell or sit on the surface of the rough endoplasmic reticulum in eukaryotic cells, (giving it the designation of "rough," in comparison to its smooth sibling that lacks ribosomes).
They receive messages from messenger RNA molecules, telling them what proteins the cell needs.
They translate these messages into protein molecules by assembling amino acids. Although the process of protein synthesis works differently in prokaryotes and eukaryotes, it is is closely related and involves ribosomes in both cases.
Related cell biology topics:
- Cell Wall: Definition, Structure & Function (with Diagram)
- Cell Membrane: Definition, Function, Structure & Facts
- Animal vs Plant Cells: Similarities & Differences (with Chart)
- Nucleus: Definition, Structure & Function (with Diagram)
- Golgi Apparatus: Function, Structure (with Analogy & Diagram)
- What Happens to the Nuclear Membrane During Cytokinesis?
- Arizona State University: Ask a Biologist: Prokaryotes vs. Eukaryotes
- Napa Valley College: Introduction to Cells: Prokaryotes and Eukaryotes
- Biology LibreTexts: Prokaryotes
- Community College of Baltimore County: Horizontal Gene Transfer
- Palomar College: Major Divisions of Life
- Idaho Public Television: Kingdoms of Life: Facts
- Florida State University: Molecular Expressions: Bacterial Cell Structure
- Western Washington University: Comparing Prokaryotic and Eukaryotic Cells
- British Society for Cell Biology: Ribosome
About the Author
Rebecca E. received a degree in human development before attending graduate school in writing. She has an extensive background in cognition and behavior research, particularly the neurological bases for personality traits and psychological illness. As a freelance writer, her specialty is science and medical writing. She's written for Autostraddle, The Griffith Review and The Sycamore Review.