In this video, we're going to introduce pili. And so the surface of bacterial cells can have relatively long filamentous protein structures that are called pili. And so pili is actually the plural form of the word. The singular form is pilus. And so these pili are protein filaments that extend from the surface of the cell. And these extensions can have varied functions. And so if we take a look at this image down below, notice that we're showing you a bacterial cell right here and extending off is this long filamentous protein structure that we call a pilus. And the pilus can have varied functions depending on the cell type. And so we'll get to talk about some of the main types of functions of pili in our next lesson video. So I'll see you all there.
Pili - Online Tutor, Practice Problems & Exam Prep
Pili
Video transcript
Functions of Pili
Video transcript
In this video, we're going to talk about some of the functions of pili. Pili typically number in only 1 to 2 per cell. Although pili can have many different functions, generally pili have 2 primary functions that we have numbered down below, 12.
The first primary function of pili is cell motility. Motility is really just referring to the ability of an organism to move through its environment. You can see that in this image, the bacterial cell here is using its pilus to move from the starting point to the finish line over here. Pili can be used for cell motility, for a cell to propel itself and move itself through its environment.
The second primary function of pili is for DNA transfer. The pilus can be used as somewhat of a bridge to connect one cell to a neighboring cell. This pilus can be used as a bridge or a tunnel to transfer DNA from one cell, and transfer that DNA to a neighboring cell. You can see here that the DNA is almost like a gift, and bacterial cells are able to exchange DNA with neighboring cells by using their pili.
This is something that we'll be able to talk more about as we move forward in our course. But for now, this here concludes our brief introduction to the functions of pili. I'll see you all in our next video.
Which of these are true about pili?
Cell Motility by Pili
Video transcript
In this video, we're going to talk about how pili can be used for cell motility or cell movement. Pili are actually involved in two types of cell motility that we have numbered down below: 12. The first type of cell motility in which pili are involved is twitching motility. Twitching motility can be described as the pili itself extending from the cell, attaching to a surface, and then retracting in order to drag the cell forward. During this period, the cell is actually moving towards its destination in a twitching-like or a jerking-like motion. This is where it gets its name, twitching motility. Notice that with this, the bacteria will be extending its pilus, attaching its pilus to an area that's further along the destination, and then retracting its pilus to pull the bacterial cell forwards in the direction of its movement. It is going to be a twitching or a jerking type of movement that is not going to be continuous and will appear very twitch-like.
On the other hand, the second type of motility that pili are involved in is gliding motility. In gliding motility, there is going to be a smooth movement that does not have a twitch-like or a jerk-like effect. The movement of the cell along the axis will be smooth. There are motor proteins involved with this process that will attach to the surface surrounding the cell. However, the exact mechanism of this is unknown. Looking at our image down below at the gliding motility, you will notice that there are motor proteins involved, and the pili is also going to be involved in some way, but ultimately the cell movement is going to be very smooth and will not be twitch-like. You can see we have the motor proteins labeled here. The significant difference is that both twitching motility and gliding motility somehow involve a pilus. Twitching motility is going to be in a twitch-like or jerk-like fashion, whereas gliding motility is going to be in a smooth-like fashion.
This concludes our brief introduction to cell motility by pili, and we'll be able to get some practice as we move forward. I'll see you all in our next video.
________ is the mechanism where a bacterial cell uses its pili to crawl across a surface towards a destination:
Scientists believe some bacteria are able to 'glide' through their environment by…
Which cellular structures are involved in conjugation?
Sex Pilus
Video transcript
In this video, we're going to introduce the sex pilus. The sex pilus is also referred to as the conjugation pilus. It connects two cells directly for a special type of DNA transfer known as conjugation. Conjugation can be defined as the process by which DNA is transferred from one bacterial cell to another by using direct contact through the sex pilus or the conjugation pilus. This transferred DNA, occurring via conjugation, can add new functions to a cell, such as resistance to antibiotics.
Looking at the image below, we can better understand how the sex pilus can bring two cells together to directly transfer genetic material. In this part of the image, we see two bacterial cells; bacterial cell A and bacterial cell B. Bacterial cell A has a yellow circle representing a DNA plasmid, possibly conferring antibiotic resistance. However, cell B does not have this yellow circle, indicating sensitivity to antibiotics.
The green structure seen here is the sex pilus itself, which brings the two cells into closer proximity. This action allows the DNA plasmid to be copied and transferred to cell B. Both cells A and B eventually possess the plasmid, highlighting its transfer through the action of the sex pilus. Now, cell B can also transfer this DNA to other cells. This is accomplished through the action of their own sex pili, demonstrating the recurring potential of this process. This concludes our lesson here, and I'll see you all in our next video.
Which of the following is NOT a function of pili?
