Bacterial Chromosome Structure & Function: How Many Chromosomes Do Bacteria Have?

Joanna Tatomir, Bridgett Payseur
  • Author
    Joanna Tatomir

    Joanna holds a PhD in Biology from the University of Michigan and is currently working towards a degree in Veterinary Medicine at Michigan State University. She has taught a combination of ESL and STEM courses to secondary and university students.

  • Instructor
    Bridgett Payseur

    Bridgett has a PhD in microbiology and immunology and teaches college biology.

Learn about the bacterial chromosome and compare the bacterial chromosome function to the human chromosome. Understand the bacterial chromosome structure. Updated: 01/27/2022

Understanding DNA and Chromosomes

Living organisms are defined by a specific set of traits and characteristics that specifies how each organism looks, behaves, and interacts with its environment. These traits and characteristics are determined by DNA, or deoxyribonucleic acid, molecules that consist of nucleotides arranged into complementary base pairs. Each set of three base pairs forms a codon, which represents the basic language used for determining the genetic code of a biological organism.

DNA consists of long threads of proteins arranged into chromosomes. Chromosomes represent the basic unit of inheritance in living organisms, as these structures undergo replication in order to code for specific proteins and to facilitate cellular replication. In chromosomes, DNA is wound around spools of protein known as histones to form chromatin. Chromatin represents tightly packed DNA wrapped around proteins, or histones, that form the arms of the chromosomes visible under a microscope.

In living organisms, DNA codes for proteins that carry out many of the basic processes needed to sustain life. Furthermore, chromosomes containing this DNA undergo replication in order to facilitate reproduction and the creation of new cells. Bacteria represent prokaryotic organisms lacking membrane bound organelles such as the nucleus and the endoplasmic reticulum. Despite the absence of membrane bound organelles, bacteria still possess genetic information encoded by DNA. In this lesson, the function and structure of chromosomes in bacteria will be discussed, as well as other types of genetic material found in bacteria.

Some Background on DNA

DNA: those three little letters have a lot of meaning. You've probably heard DNA called 'the building blocks of life' in a science fiction movie. DNA takes the shape of a double helix, often described as looking like a twisted rope ladder. The DNA is wrapped up around protein to make a material called chromatin. One long piece of chromatin is called a chromosome. You can remember this by thinking of a scarf. The material is the yarn (chromatin), and one long piece of the yarn (chromosome) is a scarf.

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How Many Chromosomes Do Bacteria Have?

Humans possess 23 pairs of chromosomes for 46 chromosomes in total, with one set of 23 chromosomes inherited from the mother and the second set of 23 chromosomes inherited from the father. In humans and other eukaryotic organisms with membrane bound organelles, these chromosomes are linear in shape and often compacted into chromatin to form the x- and y-shaped chromosomes with which many individuals are familiar. The presence of multiple chromosomes in eukaryotes is necessary in order to account for the complex traits found in plants and animals.

Bacteria, unlike plants and animals, represent prokaryotic organisms lacking membrane bound organelles. Do bacteria have chromosomes? If so, how many chromosomes do bacteria have? Although unicellular in structure, bacteria nonetheless represent living organisms with the need for genetic material to code for their traits. Therefore, bacteria, as with plants and animals, possess chromosomes. However, unlike humans, bacteria possess only one chromosome, which is circular, rather than linear, in shape.

Bacterial Chromosome Function

In both humans and bacteria, chromosomes contain the genetic code needed to sustain basic life processes and to facilitate reproduction. As humans grow and develop, cells undergo constant division in order to form new cells and to replace old or injured cells. Chromosomes, therefore, serve similar functions in both humans and bacteria. In all living organisms, the main function of chromosomes is to ensure that DNA is copied without errors and that copies of DNA are transferred to newly formed cells. Even in bacteria, which only have a single circular chromosome, bacterial chromosomes still serve the same purpose- to ensure that DNA is copied correctly and that newly formed bacteria cells possess copies of this DNA.

More specific bacterial chromosome functions include:

  • Transcription: the process by which RNA is synthesized based on the genetic code found in DNA
  • Translation: the formation of proteins based on the amino acid sequence contained in the RNA strand

The result of these two processes is the formation of the proteins and enzymes needed by the bacteria to carry out basic metabolic processes such as cellular respiration and asexual reproduction via binary fission (in which one cell divides into two).

Bacterial Chromosome Structure

Just as human chromosomes are formed by two strands of DNA, bacteria also possess chromosomes made of double stranded DNA. However, rather than being linearly arranged, the chromosomes in bacteria are arranged like a circle, with each end of the DNA bonded together to form a complete circle. As with human chromosomes, the circular chromosomes found in bacteria are also condensed to form a supercoil that can fit within the small confines of the bacterial cell.

What Are Chromosomes?

Human cells have 46 chromosomes. So what do all these chromosomes do? Chromosomes, as mentioned earlier, are made from DNA. They have all of the genetic information a cell needs to make all its proteins and do all of its cell activities. Each piece of information is called a gene; a gene tells the cell how to make one specific protein. In humans, the chromosomes are separated from the rest of the cell in the nucleus.

Bacteria, of course, are very different than humans. Bacterial cells tend to be much smaller and simpler. Most bacteria only have one chromosome. Rather than being open-ended like human chromosomes, bacterial chromosomes are circular. This doesn't mean that the chromosome is a perfect circle - it's not. It simply means that the ends of the chromosome are joined together. The chromosome itself will have folds so that it can fit into the bacterial cell.

The chromosome is found in a structure called the nucleoid. It's kind of like the nucleus in human cells, but it's not exactly the same. The nucleoid does not have a membrane like the human nucleus does, so the DNA isn't separated from the rest of the cell. The DNA is wrapped up around the creatively named DNA binding proteins, which are like they sound, proteins that bind to DNA. This helps with packaging the chromosome so it can fit in the cell, just like the folds mentioned in the previous paragraph.

Other Genetic Material in Bacteria

It's easy to think of bacteria as cells that don't do much, copying themselves without changing. But that's not actually the case. Bacteria are very versatile organisms. Many bacteria can even share genetic information with other bacteria, even if they're different species!

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Video Transcript

Some Background on DNA

DNA: those three little letters have a lot of meaning. You've probably heard DNA called 'the building blocks of life' in a science fiction movie. DNA takes the shape of a double helix, often described as looking like a twisted rope ladder. The DNA is wrapped up around protein to make a material called chromatin. One long piece of chromatin is called a chromosome. You can remember this by thinking of a scarf. The material is the yarn (chromatin), and one long piece of the yarn (chromosome) is a scarf.

What Are Chromosomes?

Human cells have 46 chromosomes. So what do all these chromosomes do? Chromosomes, as mentioned earlier, are made from DNA. They have all of the genetic information a cell needs to make all its proteins and do all of its cell activities. Each piece of information is called a gene; a gene tells the cell how to make one specific protein. In humans, the chromosomes are separated from the rest of the cell in the nucleus.

Bacteria, of course, are very different than humans. Bacterial cells tend to be much smaller and simpler. Most bacteria only have one chromosome. Rather than being open-ended like human chromosomes, bacterial chromosomes are circular. This doesn't mean that the chromosome is a perfect circle - it's not. It simply means that the ends of the chromosome are joined together. The chromosome itself will have folds so that it can fit into the bacterial cell.

The chromosome is found in a structure called the nucleoid. It's kind of like the nucleus in human cells, but it's not exactly the same. The nucleoid does not have a membrane like the human nucleus does, so the DNA isn't separated from the rest of the cell. The DNA is wrapped up around the creatively named DNA binding proteins, which are like they sound, proteins that bind to DNA. This helps with packaging the chromosome so it can fit in the cell, just like the folds mentioned in the previous paragraph.

Other Genetic Material in Bacteria

It's easy to think of bacteria as cells that don't do much, copying themselves without changing. But that's not actually the case. Bacteria are very versatile organisms. Many bacteria can even share genetic information with other bacteria, even if they're different species!

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Frequently Asked Questions

Are bacterial chromosomes circular or linear?

Unlike humans, which have linear chromosomes, bacterial chromosomes are circular. Moreover, the circular chromosomes of bacteria are located in the nucleoid region, rather than in the nucleus, a membrane bound organelle.

Do bacteria have chromosomes?

Bacteria represent a form of life that is considered to be prokaryotic, meaning that these organisms lack membrane bound organelles. Because they are a form of life, bacteria possess circular chromosomes that carry their genetic information.

What is the function of bacterial chromosome?

All chromosomes carry the genetic information needed for reproduction. In bacteria, just as with other living organisms, the function of the bacterial chromosome is to carry the genetic information for that species of bacteria.

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