Prokaryote

Tiny living things are all around us.

These things are very small. They do not have a center to hold their parts.

They can live in very hot places. They can also live in very cold places. Some live in the soil or the sea. Some even live on our bodies. These tiny things help our world in many ways.

Prokaryotes are tiny living things. Most are made of just one cell.

These cells are very simple. They do not have a nucleus. A nucleus is a center that holds DNA. They also lack other special parts. These parts are called organelles.

Prokaryotes are split into two groups. These groups are Bacteria and Archaea.

They can live almost anywhere. Some like very hot water. Others like very cold soil. Some live in the deep sea. Some even live on our bodies.

Many prokaryotes live in groups. They make a sticky layer called a biofilm.

These groups help move water. This brings oxygen to the cells. This makes them act like a bigger living thing. Some prokaryotes can even make methane. This is a gas. They have been on Earth for a long time. Some fossils are 3.5 billion years old.

Prokaryotes are tiny living things made of just one cell.

They are very different from the cells in plants or animals. Most cells have a nucleus, which is a special center that holds DNA. Prokaryotes do not have a nucleus or other enclosed parts called organelles. They also lack mitochondria, which are parts that help cells make energy. Instead, their DNA sits in a simple area called the nucleoid region. These simple cells are very important for life on Earth. They can live in places that are too harsh for most other living things.

How do these tiny cells work?

A prokaryote has a cell membrane to control what goes in and out. Many have a tough cell wall to give them shape and protection. Some even have a sticky outer layer called a capsule. To move around, some use a long, whip-like part called a flagellum. Inside, a watery gel called cytoplasm holds everything together. To make more of themselves, they use a way called binary fission. This is a type of asexual reproduction where one cell divides into two. They can also swap DNA with neighbors through horizontal gene transfer.

Scientists have spent a long time studying these organisms.

In 1962, researchers Roger Stanier and C. B. van Niel helped define the difference between prokaryotes and eukaryotes. They used terms first suggested by Édouard Chatton in 1937. Later, in 1977, Carl Woese made a big discovery. He showed that prokaryotes should be split into two groups: Bacteria and Archaea. This created the three-domain system we use today. This system includes Bacteria, Archaea, and Eukaryota. This helped us understand how all life is related.

Prokaryotes come in many shapes and sizes.

Some are shaped like spheres, which are called cocci. Others are shaped like cylinders, called bacilli, or even spirals. Most are very small, between 1 and 10 micrometers. However, some can be huge, like Thiomargarita namibiensis, which reaches 750 micrometers. Some live in extreme places, like the hot Grand Prismatic Spring.

These are called extremophiles. Others, called methanogens, live in places without oxygen and release methane gas.

Even though they are single cells, they often live together.

They can build sticky communities called biofilms. These biofilms can be very thick and complex. They use tiny channels to move water and oxygen through the group. This helps them act more like a large, organized living thing. Some prokaryotes even live inside our own bodies as symbionts. This shows how closely these tiny cells are linked to all life.

Prokaryotes are microscopic organisms consisting of a single cell.

The name comes from Ancient Greek words meaning "before" and "nut," referring to the lack of a nucleus. Unlike eukaryotes, which have a nucleus to house their DNA, prokaryotes lack membrane-bound organelles. This means they do not have mitochondria or other enclosed internal compartments. Instead, their genetic material is located in an area called the nucleoid region. This fundamental difference in cellular organization separates prokaryotes from all other forms of life.

The internal structure of a prokaryote is quite efficient. A cell membrane surrounds the cytoplasm, which is a watery gel containing enzymes and salts. Many prokaryotes possess a cell wall to provide shape and protection. Some also have a glycoprotein capsule on the outside of the membrane. To produce proteins, they use structures called ribosomes. For movement, many cells use a flagellum, which is a long, whip-like protrusion. While they lack complex organelles, some bacteria have microcompartments enclosed in protein shells. They also have a simple cytoskeleton that allows for movement within the cell.

Prokaryotes are divided into two distinct domains: Bacteria and Archaea.

This division was proposed by Carl Woese in 1977. He used molecular phylogenetics to show major genetic differences between the two groups. While they were once grouped together in a single empire, we now recognize them as separate. Eukaryotes form a third domain, but they may actually be part of the archaean clade. This is because eukaryotes share multiple homologies, or similar traits, with Archaea. This modern three-domain system provides a much clearer map of life's history.

Reproduction in prokaryotes is primarily asexual through a process called binary fission. In this process, one cell divides to create two identical cells. However, they also engage in horizontal gene transfer to exchange genetic information. In bacteria, this happens through three specific methods. Transduction occurs when a virus called a bacteriophage carries bacterial DNA to another cell. Conjugation involves the transfer of plasmids, which are small pieces of DNA, between bacteria. Natural transformation is when a bacterium takes up DNA from the water around it. For transformation to work, a bacterium must reach a state called competence.

Although they are unicellular, many prokaryotes live in large, stable communities called biofilms. They secrete an extracellular polymeric substance, or EPS, to hold the community together. These biofilms can be structurally complex, containing microcolonies and water channels. These channels act like a simple circulatory system to move oxygen to the cells. Biofilms can be up to 100 times more resistant to antibiotics than free-living cells. Some species, like Myxobacteria, even have multicellular stages in their life cycles.

Prokaryotes are incredibly diverse in their environments and metabolisms. They can be found in Antarctica or near hot undersea hydrothermal vents. Some are extremophiles, which are organisms that thrive in harsh conditions. Thermophiles love high temperatures, while halophiles prefer high salinity. Others, called methanogens, live in environments without oxygen and release methane. Some bacteria are even pathogenic, meaning they cause diseases in humans. Others live in symbiosis, meaning they live on or inside other organisms.

The history of prokaryotes is tied to the very beginning of life. The oldest fossilized prokaryotes date back approximately 3.5 billion years. This was only about 1 billion years after the Earth's crust formed. Eukaryotes appeared much later, with the oldest fossils being about 1.7 billion years old. One theory for how eukaryotes evolved is called symbiogenesis. This theory suggests that eukaryotes arose from a merger of two prokaryotes. Specifically, an archaean and an aerobic bacterium merged to create the first eukaryote. A second merger involving a cyanobacterium is thought to have created green plants.