Eukaryotes are single-celled organisms with a nucleus (a small ball) surrounded by membrane-enclosed organelles called cells. They include all single-celled animals, plants, fungi, protists and bacteria. All these organisms have one thing in common: they lack a nucleus but instead contain many different types of organelles called chromosomes.
The word “eukaryote” comes from the Greek words eu meaning “all” and karyos meaning “kind”. The first two letters stand for the Greek letter alpha and beta.
Eukaryotes are single-celled organisms such as animals (e.g. Amoeba, Paramecium), plants (red and green algae, land plants) or even some bacteria.
The three major groups of eukaryotes are the protists, animals and plants.
Most eukaryotes have a membrane-bound nucleus (a small ball) with multiple chromosomes inside it. These multiple chromosomes contain most of the genetic information which is required to make a living cell. These cells also contain other sub-cellular organelles, such as mitochondria (“little mitochondrion” in ancient Greek), lysosomes (a type of vesicle), vacuoles, the endoplasmic reticulum (a membranous network) and a cytoskeleton.
Most animal and plant cells contain a cell wall made of flexible molecules.
Some eukaryotes are multicellular while others are not. The three domains of life are:
The Archaeplastida or plant kingdom,
or plant kingdom, The Neomura or animal kingdom, and
or animal kingdom, and The Holomembria or protist kingdom.
Some eukaryotes are capable of photosynthesis (like red or green algae and plants) while others are not. Most humans belong to the animal kingdom.
Eukaryotes are classified by their membrane-bound nucleus with many chromosomes inside it, several sub-cellular organelles (mitochondria, lysosomes, vacuoles, the endoplasmic reticulum, and a cytoskeleton) as well as a cell wall made of flexible molecules.
Eukaryotes are also called as nucleated or complex cells. Prokaryotes, on the other hand, lack a membrane-bound nucleus and other organelles. They also lack a cell wall and are simpler than eukaryotes.
Bacteria (like E. coli and Salmonella) and blue-green algae are prokaryotes.
The word eukaryote comes from the Greek words: eu meaning “well” and karyos meaning “nucleus”.
Eukaryotic cells are more complex than prokaryotic cells. In addition to a nucleus and organelles, eukaryotic cells have a cytoskeleton, a cell membrane, and membrane-bound organelles.
The cytoskeleton is a network of fibrous proteins that support the cell, give it its shape, and help it move. It is located just inside the cell membrane.
The cell membrane is the boundary between the inside and outside of a cell. It is a double layer of molecules that surrounds the cell and acts as a barrier.
Sources & references used in this article:
- The revised classification of eukaryotes (SM Adl, AGB Simpson, CE Lane… – Journal of eukaryotic …, 2012 – Wiley Online Library)
- The tree of eukaryotes (PJ Keeling, G Burger, DG Durnford, BF Lang… – Trends in ecology & …, 2005 – Elsevier)
- Comparative genomics of the eukaryotes (GM Rubin, MD Yandell, JR Wortman, GL Gabor… – …, 2000 – science.sciencemag.org)
- The COG database: an updated version includes eukaryotes (RL Tatusov, ND Fedorova… – BMC …, 2003 – bmcbioinformatics.biomedcentral …)
- Repeated genes in eukaryotes (EO Long, IB Dawid – Annual review of biochemistry, 1980 – annualreviews.org)
- The deep roots of eukaryotes (SL Baldauf – Science, 2003 – science.sciencemag.org)
- The diversity of eukaryotes (DJ Patterson – the american naturalist, 1999 – journals.uchicago.edu)
- DNA repair in eukaryotes (RD Wood – Annual review of biochemistry, 1996 – annualreviews.org)