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Bacterial Chromosome: Definition & Structure

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  • 0:08 Some Background on DNA
  • 0:38 What Are Chromosomes?
  • 1:59 Other Genetic Material…
  • 3:07 Lesson Summary
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Lesson Transcript
Instructor: Bridgett Payseur

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

You have chromosomes in your cells that allow you pass on genetic information, and so do bacteria. Bacteria have single, circular chromosomes, along with extra pieces of DNA called plasmids. The chromosomes and plasmids store all of a bacterium's DNA.

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!

Of course, moving DNA from one bacterium to another would be difficult if the whole chromosome was moved. So bacteria have devised a much simpler way to share information: they pass on smaller pieces of circular DNA called plasmids. They're like a USB drive, being able to transfer data from one computer to another.

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