Gram-positive Solution – Bacteria

by Vincent Racaniello, PhD

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    00:00 Let's take a look now at the gram-positive solution in some detail so we can understand how it works. The outer layer of the gram-positive bacteria consists of this thick layer of peptidoglycan which can also be called Murein. Embedded in the murein layer are what we call teichoic acids and lipoteichoic acids. There are also proteins on the outer surface of the peptidoglycan and of course all this is on top of the cell membrane, which is a typical lipid bilayer made of phospholipids, there are proteins that are embedded in this membrane and we will talk about those functions in a minute. So here is an overview of this whole gram-positive solution, again the thick murein on top of the cell membrane and the function of the murein is to protect the cell membrane, it excludes hydrophobic chemicals which tend to be the dangerous ones. So let's look at this in a little more detail.

    01:08 So the thick cell wall again is called peptidoglycan or murein. It's a polymer of sugars and amino acids. This structure is unique to bacteria, we don't find it anywhere else in the kingdom of life and that's why we can target its synthesis using antibiotics and we'll talk about that in another lecture. As I said, this cell wall is hydrophilic, so hydrophilic compounds which the bacteria need can pass through it, but hydrophobic compounds which are typically the dangerous ones are excluded, so for example we have in our intestines bile salts to help us digest, these are very detrimental to bacteria, but the peptidoglycan actually can resist the bile salts so many bacteria can pass through our stomach and intestine to infect us. This outer layer of the gram-positive bacteria, the peptidoglycan or the murein is a polymer that forms a very protective sac around the bacterium. It consists of glycan chains of alternating N-acetylglucosamine and N-acetylmuramic acid which you can see here, and there many layers of these sugars, they are connected together by two short peptides made up of short amino acids. So this basically gives us a two-dimensional network, which is sort of like the chain mail that Knights used to wear over them, that was made of metal to protect them. You can imagine the murein or the peptidoglycan is really something very similar.

    02:46 Now remember that this thick layer is sitting over the cell membrane, the murein or the peptidoglycan, what we call the cell wall, embedded in it are teichoic acids or lipoteichoic acids, these are polymers of a sugar alcohol, either ribitol or glycerol, linked by phosphodiester bonds. And these molecules play a role in pathogenesis, they allow the bacteria to adhere to specific tissues. These are the components of these teichoic acids, on the left is glycerol teichoic acid, in the bracket is the basic subunit, the glycerol, and then that is repeated over and over to make the long chain and they are linked by phosphodiester bonds. On the right is ribitol teichoic acid, it is a different glycerol alcohol, it happens to be a bit longer.

    About the Lecture

    The lecture Gram-positive Solution – Bacteria by Vincent Racaniello, PhD is from the course Microbiology: Introduction.

    Included Quiz Questions

    1. Peptidoglycans
    2. Lipids
    3. Carbohydrates
    4. Proteins
    5. Phospholipids
    1. It is hydrophilic
    2. It is nonpolar
    3. It is hydrophobic
    4. It is impermeable
    1. Teichoic acids
    2. Murein
    3. Phospholipids
    4. Glucose
    5. Triglycerides

    Author of lecture Gram-positive Solution – Bacteria

     Vincent Racaniello, PhD

    Vincent Racaniello, PhD

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