Gram-Positive vs. Gram-Negative Cell Walls - Online Tutor, Practice Problems & Exam Prep

Gram-positive and gram-negative bacteria differ significantly in structure. Gram-positive bacteria possess a thick peptidoglycan layer and teichoic acids, while gram-negative bacteria have a thin peptidoglycan layer, an outer membrane containing lipopolysaccharides (LPS), and porins. The presence of LPS in gram-negative bacteria contributes to their pathogenicity. A mnemonic to remember these differences is "long PowerPoint," highlighting the association of LPS and outer membranes with gram-negative cells, and the thicker peptidoglycan layer in gram-positive cells.

Gram-Positive vs. Gram-Negative Cell Walls

In this video, we're going to do a side-by-side comparison of gram-positive versus gram-negative cells. In this video, we're only going to be reviewing information that we already covered in our previous lesson videos. Since there's no new information being covered, if you're already feeling really good about the differences between gram-positive and gram-negative cells, then feel free to skip this video if you'd like. However, if you're struggling or need just a little bit more help, then feel free to stick around because this video might be very helpful for you. Notice that down below, we have an image that is organized into a table. On the left-hand side, we are focusing on gram-positive cells, whereas on the right-hand side, we're focusing on gram-negative cells. Keep that in mind.

One thing to note is that, in both gram-positive and gram-negative cells, there is a plasma membrane. All cells have a plasma membrane. That is something that is similar between the two. They both also have a periplasm or periplasmic space, which is the space or the gel-like fluid between the peptidoglycan and the cell membrane or the plasma membrane. They both have a plasma membrane and a periplasm. Now, in terms of the peptidoglycan layer, notice that the gram-positive cells on the left have a thick layer of peptidoglycan that is very thick here in comparison to the layer of peptidoglycan with gram-negative cells, which is very thin. The gram-negative cells are going to have lipoproteins that help anchor the entire outer membrane to the peptidoglycan layer. The outer membrane is going to have lipopolysaccharides in it, or endotoxin or LPS. Embedded within this outer membrane are also going to be porins that will allow molecules to be transported across the membrane. The gram-positive cells have tectonic acids. There are lipoteichoic acids which will connect directly to the cell membrane or the plasma membrane. And then there are wall teichoic acids, which do not connect directly to the plasma membrane, and instead, they're mainly embedded in the peptidoglycan layer.

Down below, what we have is this little chart that helps to summarize a lot of those important key features. In terms of the outer membrane, gram-positive cells do not have an outer membrane. That outer membrane is specific to gram-negative cells. The outer membrane is going to be present in gram-negative cells. In terms of the peptidoglycan layer, both gram-positive and gram-negative cells have cell walls made of peptidoglycan. However, with gram-positive cells, they have a thick layer of peptidoglycan, whereas in gram-negative cells, they have a thin layer of peptidoglycan. That is being represented up above as well where you can see the thick layer of peptidoglycan in gram-positive and the thin layer of peptidoglycan in the gram-negative. In terms of tectoid acids, gram-positive cells are going to have teichoic acids. So they will be present in gram-positive cells. However, in gram-negative cells, the teichoic acids are absent. So gram-negative cells do not have teichoic acids. The lipopolysaccharides are going to be absent in gram-positive cells, but they will be present in gram-negative cells. This little chart right here summarizes many of the most important and most tested differences between gram-positive and gram-negative cells. It summarizes those key differences and is a good little chart to be able to study from. This here concludes our brief review of the main differences between gram-positive and gram-negative cells. We'll be able to get some more practice as we move forward, so I'll see you all in our next video.

Mnemonic for Gram-Positive vs. Gram-Negative Cell Walls

This video we're going to talk about a mnemonic or memory tool to help you remember the key differences between gram positive and gram negative cells. And so really this mnemonic is, down here in this image. And the mnemonic is just long PowerPoint or ppt, since PPT is an abbreviation for PowerPoint. And so all you need to do is think about those long PowerPoints that your professors use during lecture. And so when you think about long PowerPoint, this can help you remember that lipopolysaccharides or LPS or endotoxin, as well as an outer membrane are associated with gram negative cells, and they are not associated with gram positive cells. And then the PowerPoint over here can help remind you that, gram positive cells have a thick peptidoglycan layer, although they both have peptidoglycan. Gram positive cells have a thicker peptidoglycan layer, and so that's why we have the peptidoglycan associated here. And gram positive cells also have teichoic acids that are specific to gram positive cells, and they are not found in gram negative cells. And so all you have to do is think about those long, boring PowerPoints that your professors use, and that can help you remember this little memory tool here. And so hopefully that will be helpful to you guys in some way. And I'll see you guys in our next video.

Which of the following is not a chemical component of a bacterial cell wall?

• A. Cellulose
• B. Lipoproteins
• C. Peptidoglycan
• D. N-acetylmuramic acid
• E. Teichoic acids

Gram negative cell walls contain fewer layers of _____ than gram positive cell walls.

• A. LPS
• B. Peptidoglycan
• C. Lipid A
• D. Mycolic acids
• E. Phospholipids

Here’s what students ask on this topic:

What are the main differences between gram-positive and gram-negative cell walls?

Gram-positive and gram-negative bacteria have distinct cell wall structures. Gram-positive bacteria have a thick peptidoglycan layer and teichoic acids, which provide rigidity and structural support. In contrast, gram-negative bacteria have a thin peptidoglycan layer, an outer membrane containing lipopolysaccharides (LPS), and porins. The outer membrane in gram-negative bacteria contributes to their resistance to certain antibiotics and detergents. Additionally, the presence of LPS in gram-negative bacteria is associated with increased pathogenicity. These structural differences are crucial for the bacteria's interaction with their environment and their response to antibiotics.

Why do gram-negative bacteria have an outer membrane?

Gram-negative bacteria have an outer membrane to provide an additional protective barrier. This outer membrane contains lipopolysaccharides (LPS), which contribute to the bacteria's pathogenicity and can trigger strong immune responses in hosts. The outer membrane also contains porins, which are protein channels that allow the passage of small molecules and nutrients while restricting harmful substances. This structure helps gram-negative bacteria resist certain antibiotics and detergents, making them more resilient in hostile environments compared to gram-positive bacteria.

How does the thickness of the peptidoglycan layer differ between gram-positive and gram-negative bacteria?

The peptidoglycan layer in gram-positive bacteria is significantly thicker than in gram-negative bacteria. In gram-positive bacteria, the peptidoglycan layer can be up to 20-80 nm thick, providing substantial structural support and rigidity. In contrast, gram-negative bacteria have a much thinner peptidoglycan layer, typically around 2-7 nm thick. This thin layer is located between the inner plasma membrane and the outer membrane, which contains lipopolysaccharides (LPS) and porins. The thick peptidoglycan layer in gram-positive bacteria is a key feature that differentiates them from gram-negative bacteria.

What role do teichoic acids play in gram-positive bacteria?

Teichoic acids are important components of the cell wall in gram-positive bacteria. They are polymers of glycerol or ribitol phosphate and are embedded within the thick peptidoglycan layer. Teichoic acids play several roles, including maintaining cell wall structure, regulating cell growth, and providing rigidity. They also contribute to the bacteria's ability to adhere to surfaces and interact with the host's immune system. There are two types of teichoic acids: wall teichoic acids, which are linked to the peptidoglycan, and lipoteichoic acids, which are anchored to the plasma membrane. These acids are absent in gram-negative bacteria.

What is the significance of lipopolysaccharides (LPS) in gram-negative bacteria?

Lipopolysaccharides (LPS) are crucial components of the outer membrane in gram-negative bacteria. LPS molecules consist of a lipid A, a core polysaccharide, and an O-antigen. Lipid A is responsible for the toxic effects of LPS, making it an endotoxin that can trigger strong immune responses in hosts. The core polysaccharide and O-antigen contribute to the structural integrity and surface properties of the bacteria. LPS plays a significant role in the pathogenicity of gram-negative bacteria, helping them evade the host's immune system and resist certain antibiotics. This makes infections caused by gram-negative bacteria particularly challenging to treat.