Skip to main content
Search

Introduction to plasmid biology

Published on January 28, 2008 Reviewed on October 20, 2024   31 min

A selection of talks on Methods

Please wait while the transcript is being prepared...
0:00
Welcome to the Henry Stewart Talks series on the biology and significance of plasmids. My name is Don Clewell, and I'll be giving the first lecture, An Introduction to Plasmid Biology.
0:15
What is a plasmid? This is a microbial cell, in this case, a bacterial cell, we see it has two DNA molecules. On the left, we have a rather large molecule corresponding to the chromosome; and on the right, we have a plasmid being, a small, physically separate molecule capable of maintaining itself autonomously in this particular state.
0:39
Plasmids can be found in all three domains of life. They're extremely common in prokaryotes, which correspond to the eubacteria or true bacteria and the Archea, which used to be lumped into the bacterial world, but now maintain an independent position corresponding to an independent domain of life called Archea. Plasmids are also common in eukaryotes, such as yeasts. These correspond to the domain Eukarya, which not only includes microorganisms, but also much higher systems, including humans.
1:13
The majority of the organisms that we'll be talking about in this series are prokaryotes, so it's worth noting a little bit about the prokaryotic world. First of all, there are millions of species on the planet, most of which have never been cultivated. For example, a gram of soil can contain as many as 5000 to 10000 species of prokaryotes. The combination of species can vary tremendously from one location to another. Similarly, in seawater, there are as many as 20000 species of prokaryotes per liter, and again, these can vary significantly from one location to another. You could even have these numbers down to great depths, down to two miles down in the ocean. A human being carries about a thousand different species of bacteria. For example, it's been estimated that there are maybe as many as 100 trillion bacterial cells in and on a human being. This compares to only about 10 trillion human cells. So in a sense, of all the cells that are present in and on the human body, only about 10% of them are human. There are huge amounts of interactions that occur between these microorganisms living together in animals, soil, and the ocean. They're all exchanging DNA quite efficiently, and this DNA transfer is known as horizontal gene transfer.

Quiz available with full talk access. Request Free Trial or Login.