Microbiology, part 39: Genetics - Horizontal Gene Transfer

Hi, I'm Cathy with Level Up RN. In this video, we are going to discuss horizontal gene transfer, including transformation, transduction, conjugation, and transposons. And at the end of the video, I'm going to give you guys a quiz to test your understanding of some of the key facts I'll be covering, so be sure to stay for that. And if you have our Level Up RN microbiology flashcards, go ahead and pull out your flashcards on horizontal gene transfer so you can follow along with me. And pay close attention to the bold red text on the back of the cards because those are the things that you are likely to get tested on.

As a reminder, vertical gene transfer is the transfer of genes from one generation to the next, so from the parent to the offspring, whereas horizontal gene transfer is the movement of genetic information between organisms in the same generation. Horizontal gene transfer allows asexual prokaryotes to acquire new traits and contributes to genetic diversity. The three main types of horizontal gene transfer include transformation, transduction, and conjugation. In addition, transposons are another mechanism of horizontal gene transfer. Let's first talk about transformation. So when cells die, their DNA is released into the environment. With transformation, this environmental DNA is taken up by a prokaryotic cell where it is recombined with the bacterial genome or can remain separate as a plasmid. So only competent bacteria are able to participate in transformation. This means that the bacterial cell is able to take up environmental DNA through pores in its cell membrane. Next, we have transduction, which is where small sequences of chromosomal DNA are moved from one bacterium to another via a bacteriophage. So a bacteriophage is a virus that infects and replicates within bacterial cells as well as archaea cells. And of note, we have a separate video that goes into details of viral replication, including generalized and specialized transduction.

Next, we have conjugation, which involves the transfer of DNA from one bacterial cell to another through direct contact using a conjugation pilus. Let's take a look at how this process works using an illustration from our microbiology flashcard deck. Let's first go over some important terms related to conjugation. The F plasmid is a small, circular, double-stranded DNA molecule located independent from the bacterial chromosome. Plasmids often contain genes that increase a cell's virulence, such as genes that encode for antibiotic resistance or the production of toxins. An F plasmid also contains genes that allow the cell to conjugate. The F-positive or donor cell is a bacterial cell that contains the F plasmid and is therefore able to form an F pilus and conjugate. The F pilus, which is also called a conjugation pilus, is a thin tube-like appendage used to transfer genetic information from one cell to another. An F-negative or recipient cell is a bacterial cell that lacks an F plasmid. So during conjugation, the pilus of the donor cell attaches to the recipient cell and then contracts, which draws the cells together. A cytoplasmic bridge then forms between the two cells and one strand of the double-stranded F plasmid is transferred from the donor cell to the recipient cell. The donor cell then synthesizes a complementary strand to restore the plasmid, and the recipient cell also synthesizes a complementary strand for the plasmid and is now an F-positive cell.

Lastly, let's talk about transposons, which are also referred to as jumping genes. Transposons are segments of DNA that contain inverted repeat sequences at their ends, as well as a gene that encodes for the enzyme transposase. Transposase allows the transposon to move or jump from one location on the genome to another. Non-replicative transposons move genes in a cut-and-paste-type fashion. So they will excise or cut the genes from one location and move them to a new location, whereas replicative transposons move genes in a copy-and-paste fashion. So they will copy the genes from one location and move that copy to a new location, but the genes will still remain at the original location. Of note, transposons may contain antibiotic-resistant genes, so during transposition, these genes can move from the chromosome to the plasmid. And then that plasmid is easily transferred to other bacteria during conjugation. So transposons are a significant contributor to antibiotic resistance in bacteria.

All right. It's quiz time. Are you guys ready? I have three questions for you. Question number one. Blank is a form of horizontal gene transfer where environmental DNA is taken up by a prokaryotic cell. The answer is transformation. Number two. The blank is a thin tube-like appendage used to transfer genetic information from one cell to another. The answer is the F pilus or conjugation pilus. And number three, a blank is a DNA sequence that can move from one location to another in the genome. The answer is transposon. All right. Hope you did great with that quiz, and I hope you found this video to be helpful. Take care and good luck with studying.

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Details of viral to antibiotic that contain inverted repeat sequence.