Introduction to Bacterial Cell Walls - Video Tutorials & Practice Problems
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1
concept
Introduction to Bacterial Cell Walls
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3m
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in this video, we're going to begin our introduction to bacterial cell walls. And so it's important to note that the water pressure on the inside of a bacterial cell is typically higher than its surroundings. And so there's higher water pressure on the inside of the cell and lower water pressure on the outside of the cell. And so this requires the bacterial cells to have a protective layer that surrounds the cell. And so this is why most bacterial cells have a cell wall and a cell wall can be defined as a semi rigid structural layer located on the outside of the membrane located on the outside of the cell membrane. And it is part of the cell envelope. So, recall from our previous lesson videos that the cell envelope is really just a term that's referring to all of the layers that surround the outside of the cell. And so it's the cell envelope includes. Um it's a collection of the cell wall, the cell membrane and an outer membrane as well if that outer membrane is present. So some bacteria as well learn moving forward in our course, will have two membranes. They'll have an inner membrane and then they'll also have an outer membrane. But we'll talk more about those later in our course. So down below, in our example, we're showing you how the cell wall protects the cell from rupturing from high water pressure that's found on the inside. And so here what we're showing you is that water is going towards the inside of the bacterial cell and so there is going to be high water pressure on the inside. And so this high water pressure that's on the inside of the bacterial cell is going to create the possibility of rupturing if there was not a cell wall. But thankfully most bacteria have a cell wall and so notice that the cell wall is this light blue layer that you see in between here and that cell wall is made of a molecule. It is made of a molecule that is called Pep Tito Glicken. And so you can see that we're labeling the cell wall as potato Glicken because that is the predominant molecule that makes up the cell wall. And we'll talk more about peptidoglycan as we move forward in our course. Now you'll also see that part of the cell envelope that the peptidoglycan cell wall is part of the cell envelope and the cell envelope also includes an outer membrane if it's present or capsule. And so you can see that going all the way around here. This is the outer membrane or the capsule. And then you have the peptidoglycan which is the cell wall itself uh in the light blue that goes all the way around. And then on the inside here, what you have is the inner membrane also known as the cell membrane. Well, just label here is the cell membrane. And so the cell membrane, it would be this layer. I'll do it in red. So it's easier to see. It's this layer that you see all the way around here. And so really this is showing you the outer layers that are surrounding a bacterial cell. And so we'll get to talk more about all of this here as we move forward in our course. Uh But for now, this here concludes our brief introduction to bacterial cell walls and I'll see you all in our next video.
2
Problem
Problem
Which is (are) true concerning the cell wall of prokaryotes?
A
It determines the shape of the bacteria.
B
It is part of the cell envelope.
C
It prevents the bacteria from bursting.
D
All of the choices are true.
3
concept
Peptidoglycan
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1m
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in this video, we're going to introduce Pepto Glicken. And so Pepito Glicken is a rigid mesh like polly Sacha ride and protein mixture that is the main component of specifically bacterial cell walls. And so Petito Glicken is really a molecule that is specific to bacteria and it is not really found in Arcadia or and you carry it. And so that's something that's important to keep in mind. Now Petito Glicken provides structural support and it helps to provide or maintain rigidity for the cell since it is the main component of the bacterial cell walls. And so if we take a look at our image down below notice over here we're showing you a bacterial cell and we're focusing focusing mainly on the bacterial cell wall which is again the light blue layer that goes all the way around. And so if you zoom into that light blue layer, which you'll notice is that the structure is mainly composed of pepto. Why can't. And so what you see down below right here is the structure of Pep Tito Glicken and which will note here is that it consists of poly Sacha ride. Uh These are the policy Sacco ride components uh but then it also has these protein linkages. And so really Pepto Glicken is a policy Sacco ride and protein mixture. And so we'll get to talk a lot more about the structure of Pepto Glicken uh in our next video. But for now, this year concludes our brief introduction to Pep Tito blackened and we'll be able to get some practice in our next video.
4
concept
Peptidoglycan Structure
Video duration:
4m
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in this video, we're going to talk more details about Pep Tito Glicken structure. And so Pepito Glicken consists of repeating units of two different Mono Sacha rides. And these two different mono Sacha rides are going to be linked to each other, co Vaillant lee by a special type of bond known as a Beta 14 Glick acidic linkage. And so these two different mono sacha rides are number one N, acetyl glucosamine or Nag for short and and a Seattle mirror, Amick acid or Nam for short. And so these Nag and Nam sub units are going to be repetitive li linked together to create a long chain known as a Glicken chain. So the Glad hand chain is really just a sugar chain made up of repeating units of nag and nam repetitive li linked together. And so if we take a look at our image down below, on the left hand side over here, we're showing you an image representing peptidoglycan structure and notice that it consists of multiple Glicken chain. So each of these chains is referred to as a Glicken chain. So here we're showing you three glad hand chains right here. And each of those three Glicken chains consists of repeating nag and nam subunits. So notice that the nag sub units are in blue and the nam sub sub units are in green. And notice that the nag and nam repetitive li are going to be repetitive li linked to create these Glicken chains that you see here. And so in addition to these glide hand chains, which will notice is that there's also a four amino acid chain known as a tetra peptide, since Tetra is the prefix that means for and because these are amino acids, it's going to be a protein, a small peptide. And so this tetra peptide is going to be attached to each of the nam molecules. And so this tetra peptide is going to be important for the cell wall structure to give that cell wall extra virginity. And so if we take a look at our image down below, once again, in addition to these Glicken chains, what's linking these glad hand chains are these tetra peptide units that you see here. And so these tetra peptide units are going to be very, very important to link adjacent Glicken chains together. And so if we take a look at the image over here on the right hand side, notice that it's zooming into this specific region right here and within this specific region, which will be able to notice here is that we have a uh an acetyl glucosamine molecule right here. And this is again going to be the nag sub unit. And we have over here and then a settlement ceramic acid molecule right here. And this is going to be the nam sub unit. And so notice that the nag and nam some units are linked to each other via this bond that you see here. And this bond is what we call a beta 14 Glick acidic linkage. Gleick, ascetic linkages are uh linkages that will link mono sacha rides together. And so notice that branching off of the nam sub unit is a tetra peptide. And so this tetra peptide consists of four amino acids. Uh and so you can see the tetra peptide is right here each of these circles that you see here represents an amino acid. And so we can call this these here amino acids forming this tetra peptide change. And so this year concludes our brief introduction to peptidoglycan structure and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video
The NAG and NAM molecules of peptidoglycan are connected by a:
A
A tripeptide chain
B
β-(1,4) glycosidic linkage
C
A disulfide bridge
D
β-(1,6) glycosidic linkage
E
A phosphodiester linkage
7
concept
Peptide Interbridge
Video duration:
2m
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in this video, we're going to introduce the peptide inter bridge. And so the peptide inter bridge is the cross link between tetra peptides of adjacent Glicken chains. And so if we take a look at our image down below, over here, on the left hand side, you should notice that this is the structure of Pepto Glicken. And we know that it consists of these Glicken chains which are repeating nag and nam sub units going across here. So here you can see three Glicken chains and branching off of these glad hand chains are these tetra peptides which you can see at these positions. And so these are the tetra peptides that we had talked about in our previous lesson video now, which will also notice is that in between these tetra peptides are these inter bridges which you can see here and here and here and here and so those gray little circles that you see there are amino acids that serve as the peptide inter bridge. Now. Uh these peptide inter bridges are really only found in gram positive cells. They are not going to be found in gram negative cells. And so the tetra peptides are going to be linked directly to each other in gram negative cell walls. And so you won't see peptide inter bridges in gram negative cell walls. You'll only see the peptide inter bridges and gram positive cell walls. And so this peptide inter bridge is going to be important for these grand positive cells because it helps to form an interconnected network of these pepto Glicken fibers. And so what you can see here is once again, these little bridges that I'm highlighting here and blue are the peptide inter bridges. And so this image over here on the right hand side is really just a zoom in of this specific region that you see here. And so when you zoom in, you can see the nam and nag repeating subunits branching off of the nam. You have the tetra peptides and uh linking cross linking these tetra peptides is this peptide inter bridge. And once again the peptide inter bridge is going to be this region that you see right here. And so this is going to help to give Pepito Glicken a stronger structure and help to link all of these glad hand chains together. And so this year concludes our brief introduction to the peptide inter bridge and we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video.
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Problem
Problem
The glycan chains of adjacent peptidoglycan molecules are connected by:
A
A sugar backbone
B
Phosphodiester linkage
C
A lipid bilayer
D
Polypeptide chain crosslinking
E
Disulfide linkages
9
concept
Gram-Positive & Gram-Negative Bacteria
Video duration:
2m
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in this video, we're going to continue our introduction to bacterial cell walls by talking about gram positive and gram negative bacteria. And so bacterial cells can be generally categorised based on whether or not they take up what's known as the gram stain. Now, the gram stain is a specific staining procedure that can differentiate bacteria based on differences in their cell walls. Now, later in our course, in a different video, we'll talk a lot more details about the differences between gram positive and gram negative cell walls. But for now, what you guys should know is that gram positive bacteria will absorb will absorb the gram stain whereas gram negative bacteria do not absorb the gram stain. And so let's take a look at our image down below to get a better understanding of this. And so what you'll notice is on the far left over here, what we have are some bacterial cells that are unstained. They are not stained. And after the gram staining procedure, the purple stain that's used will be absorbed by the gram positive cells. And so the grand positive cells will absorb this purple stain and so they will become purple themselves. Whereas noticed that the gram negative cells do not absorb the stain and so they do not turn purple. And so once again, the reason for why gram positive absorb the purple steen and gram negative do not absorb the purple stain has to do with differences in their cell walls. And later in our different video we'll talk more about the differences in the cell walls of gram positive and gram negative bacteria. But for now this year concludes our brief introduction to gram positive and gram negative bacteria. And we'll be able to get some practice as we move forward. So I'll see you all in our next video.
10
Problem
Problem
The Gram stain works because of differences in the ________ of bacteria.
A
Genetic characteristics
B
Cell membranes
C
Cell walls
D
Capsules
11
concept
Types of Bacterial Cell Walls
Video duration:
2m
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in this video, we're going to continue to talk more about the types of bacterial cell walls. And so the two types of bacterial cells, gram positive and gram negative bacteria are grouped by the structure of their cell walls. Now, gram positive bacteria which absorbed the gram stain, they have a sick peptidoglycan layer, whereas gram negative bacteria which do not absorb the gram stain only have a thin peptidoglycan layer. However, gram negative bacteria also had a complex outer membrane that the gram positive bacteria do not have. And so let's take a look at our image down below to get a better understanding of this. So notice on the left hand side, what we're showing you are gram positive cells. And on the right hand side we're showing you gram negative cells. And what you'll notice is that the grand positive cells over here on the right, they have a thick peptidoglycan layer. And so notice that the peptidoglycan layer is this layer here. That's m blow. It's very very very thick. Whereas if you take a look at the gram negative cells over here notice that their peptidoglycan layer is very very thin and comparison. And so here we can say that there is a thin peptidoglycan layer for gram negative cells now. Which will notice is that the grand positive cells, they do have a plasma membrane and inner membrane if you will. Which is right here, this is the plasma membrane but they do not have an outer membrane so the outer membrane is absent and grand positive cells. However, when you take a look at the gram negative cells, they have a thin potato blight hand layer but notice that they also have an outer membrane that's beyond their plasma membrane. So here's the plasma membrane. The outer membrane is this one that's out here. And so the outer membrane is going to be present for gram negative bacteria. And so these are some of the main differences between gram positive and gram negative. But there are also other differences that we'll get to talk more about as we move forward in our course. For now, this here is just the brief introduction to these two different types of bacterial cell walls, and so we'll be able to get some practice as we move forward and learn more as we move forward as well. So I'll see you all in our next video.
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