Do Bacteria have a Nucleus?
Do bacteria have a nucleus? The short answer is no; bacteria cells do not have a nucleus. Now you may be thinking that if bacteria don’t have a nucleus, what do they have instead?
To fully understand the answer, let’s dive into the structure and nature of bacteria on a cellular level.
This article will explore bacteria – how they look under a microscope, where they store their genetic material, and why they belong to prokaryotic cells. Furthermore, by the time you have finished reading, you will know the difference between prokaryotic and eukaryotic cells and where these two types of cells fit into the tree of life.
To start, let’s explore the world of bacteria – what they look like, where they live, and how they are classified by shape.
What are bacteria?
Bacteria belong to a group of organisms called prokaryotes. Prokaryote means ‘before-nucleus’ and combines the Greek words pro, meaning ‘before’, with karyon, meaning ‘kernel’ or nucleus.
Prokaryotes are single-celled microorganisms that lack a well-defined nucleus and membrane-bound organelles.
Bacteria are one of the smallest, simplest, and oldest cells on Earth. These organisms were one of the first to appear on Earth. Scientific evidence shows that bacteria existed as long as 3.5 billion years ago!
Bacteria can exist as single cells or in pairs, chains, and clusters. You will find bacteria in practically every kind of environment on Earth, including some of the most inhospitable places on the planet.
Bacteria live in soil, water, radioactive waste, acidic hot springs, and even the deep below the Earth’s surface. Moreover, millions of bacteria live inside our bodies, mostly in our gut.
Scientists often describe bacteria as dangerous bugs that make people sick. Serious bacterial diseases include cholera, tetanus, syphilis, tuberculosis, pneumonia, and bacterial meningitis.
However, while some types of bacteria can cause disease, others are actually beneficial to us. For example, some bacteria give sourdough its sour taste. Meanwhile, other bacteria live in our large intestine and help synthesize vitamin K, a critical blood clotting factor.
How are bacteria classified by shape?
Scientists can classify bacteria into five groups depending on their basic shape:
- Spiral (spirilla)
- Corkscrew (spirochaetes)
- The comma (vibrios)
- Spherical (cocci)
- Rod (bacilli)
Although bacteria vary in shape, size, and structure, the cell structure of each bacterium is similar.
Scroll down to find out what bacteria look like at a microscopic level.
What is the extracellular structure of bacteria?
Let’s take a peek at some of the major structures found on the outside of a bacterial cell:
Every organism needs to have protection from the external environment. Like humans have a layer of skin, a well-organized, tightly-packed covering encloses most bacteria called a capsule.
The capsule consists of polysaccharides (complex carbohydrates) and can enhance the ability of a bacterium to cause disease.
It serves several functions, including:
- It keeps bacteria from drying out (desiccation).
- It protects the bacterium from phagocytosis – when living cells called phagocytes ingest or engulf other cells.
- It protects the bacterium from detergents and bacterial viruses.
A rigid and complex cell wall surrounds each bacterium. The wall consists of peptidoglycan, which is a protein-sugar molecule. The function of the cell wall is to provide structural support and help maintain the bacteria’s shape.
The bacterial flagellum is a long, thin, whip-like organelle attached to the outer surface of a bacterial cell and enables bacteria to move.
Pili are short, hair-like fibers on the outside of a bacterial cell wall. While they can help with movement, the most important functions of pili are to attach a bacterial cell to different surfaces or other cells and assist in conjugation. Conjugation is when genetic material is transferred between cells.
Bacteria external structure
Protects from drying out
Structure and support
Attachment to different surfaces and transfer of genetic material
What is the intracellular structure of bacteria?
What can you find inside a bacterial cell? Let’s take a look…
The cell membrane, also known as the plasma membrane, is a biological lining that separates the interior of a bacterial cell from its outside environment.
The membrane’s primary function is to acquire nutrients, eliminate waste and maintain the bacterium in a constant, highly-organized state. The membrane also plays a role in respiration, photosynthesis, and the synthesis of lipids and cell components.
The cytoplasm is a colorless, jelly-like substance that fills the inside of bacterial cells and is surrounded by the cell membrane. It comprises 80% water, enzymes, salts, and proteins.
The cytoplasm contains cell organelles such as plasmids, ribosomes, and nucleoids. Its main functions are to assist in metabolic activities and provide shape to the cell.
Bacterial ribosomes are found all over the cytoplasm and are composed of ribosomal ribonucleic acid (rRNA). rRNA is responsible for protein synthesis. That means they translate genetic code into amino acids. Amino acids are the building blocks of proteins.
The nucleoid means “nucleus-like” and is an area in the bacterial cell’s cytoplasm where the chromosomal DNA (genetic material) can be found. The strand of DNA is not surrounded by a membrane. Rather, the nucleoid is simply an irregularly shaped region in the cytoplasm.
The primary function of the nucleoid is to control the cell’s activity and reproduction. The nucleoid is where transcription and replication of DNA take place. Most bacteria have one nucleoid. However, some bacterial species have two or more nucleoids.
Apart from a nucleoid, some bacteria have extra genetic material called plasmids. Plasmids lie in the cytoplasm and consist of a small circular piece of DNA that replicates independently of the chromosome.
While plasmids are not essential for survival, scientists believe that these pieces of DNA seem to give bacteria some competitive advantage. These benefits include antibiotic resistance and the ability to survive in harsh environments.
Bacteria internal structure
Acquire nutrients, eliminate waste, maintain a constant state
A jelly-like substance where cellular activities take place
Responsible for protein production
A region in the cytoplasm that contains the single DNA
Piece of DNA that allows antibiotic resistance
So, is the nucleoid a kind of nucleus in bacteria?
Going back to the article’s question, “do bacteria have a nucleus?”, it is clear that instead of a well-defined nucleus, bacteria have a “nucleus-like” structure called a nucleoid. The nucleoid is located in the cytoplasm and stores the genetic material.
So, if bacteria have a “nucleus-like” structure called a nucleoid, which organisms have a nucleus? Furthermore, what does it look like, and how does it control a cell’s activity?
Find out all these answers by scrolling down.
The nucleus is one of the most important organelles that you will find only in large and complex eukaryotic cells.
As you can see in the image below, the nucleus is located in the middle of the cell and is enclosed by a well-defined membrane, which contains the cell’s chromosomes. The DNA present in the chromosomes provides the genetic information that’s required for the cell’s growth and reproduction.
Unlike a bacterial nucleoid, the nucleus is surrounded by a double nuclear membrane that separates the nucleus from the cytoplasm. The nuclear membrane contains pores that allow molecules and substances, such as RNA and proteins, in and out of the nucleus.
The nucleus has two main functions:
- It’s responsible for controlling important cellular activities such as growth, cell division, protein synthesis, and many other important functions.
- It is responsible for storing the cell’s DNA.
What is the difference between nucleus and bacteria nucleoid?
There are many differences between prokaryotic and eukaryotic cells, such as size and complexity. However, the main distinction between these two cells lies in where and how the genetic material is located.
Prokaryotic cells don’t have a distinct nucleus and instead have free-floating genetic material that lies in an area called a nucleoid.
These kinds of cells are found in single-celled organisms that scientists call prokaryotes, such as bacteria.
Eukaryotic cells are larger and more complex cells compared to prokaryotic cells. They have a distinct nucleus that contains the cell’s genetic material.
These kinds of cells are found in organisms called eukaryotes and can be unicellular or multicellular. Eukaryotes include humans, plants, animals, fungi, and protists.
Now that you understand how organisms on Earth are divided into two groups on a cellular level, let’s take a closer look at how these two different cells fit into the tree of life.
What is the tree of life?
The tree of life is a metaphor that describes the idea that all life on Earth descends from a common ancestor. The term was first used by Charles Darwin.
Looking at the image above, the evolutionary tree of life consists of three domains so far: Archaea, Bacteria, and Eukarya. In biological taxonomy, a domain refers to the highest order of life classification.
Bacteria and Archaea
Bacteria and Archaea are both small, single-celled organisms made up of prokaryotic cells that have a nucleoid where their genetic material is stored. These micro-organisms are able to live in every kind of environment, including extreme temperatures and highly acidic and salty conditions.
Eukarya are multi-celled organisms that are made up of eukaryotic cells that contain a membrane-bound nucleus and organelle. There are four kingdoms that belong to Eukarya: Animals, Plants, Fungi, and Protista.
- Is Plant cell Prokaryotic or Eukaryotic?
- Is Amoeba Prokaryotic or Eukaryotic?
- Is Osmosis active or Passive?
- Is Fungi Prokaryotic or Eukaryotic?
Do bacteria have a nucleus? Main takeaways:
- Bacteria are single-celled microorganisms called prokaryotes that have existed on Earth for 3.5 million years.
- Unlike larger, more complex eukaryotic cells, bacteria do not have a nucleus to store their genetic material. Instead, these microorganisms have a nucleoid.
- The nucleoid is an irregularly shaped region in the cell’s cytoplasm where the genetic material is located.
- The distinction between a nucleus and a nucleoid led scientists to divide cells into either eukaryotic or prokaryotic cells.
- Eukaryotic cells have membrane-bound organelle and a distinct nucleus where the DNA is stored. Examples of organisms made up of eukaryotic cells include humans, plants, animals, fungi, and protists.
- In contrast, prokaryotic cells lack a well-defined nucleus and membrane-bound organelle. You will find these types of cells in single-celled organisms known as prokaryotes, such as bacteria and archaea.