The Bacterial Cell Envelope

[@mRadamaston]

there are a lot of teaching videos on youtube but this is by far the best one on this topic, thanks :)

[@ProfGillesBolduc]

Thank you.

[@MultiTonito23]

I totally agree!

[@danieladoofann138]

mRadston yes definitely the best one. Covers everything you need

[@satyam5241]

THANKS, BUDDY, HELPED ME A LOT, KEEP GOING, LOVE FROM INDIA!

[@drosso5986]

in one word " terrific " ... keep making such amazing videos

[@kf2606]

That was an awesome video! Thank you! Well done!

[@salehmohammed5961]

Perfect lecture 👌 Thank you

[@raquelpurpleboxes]

Osmosis isn't defined by the concentration of water on either side of the membrane. It's determined by the concentration of solute.

[@ProfGillesBolduc]

I think we are saying the same thing because a solution is equal to solute plus solvent (water). Osmosis is the movement of solvent across a membrane and moves from the side with high conc to the side with low. One can also say that the direction of osmosis is from low to high solute concentration.

[@raquelpurpleboxes]

@@ProfGillesBolduc Osmosis is the diffusion of water, not solute. Water is the solvent, yes. When we find the concentration of something, we do not find the ratio of solvent to solute, but the ratio of solute to solvent.

[@anthonyguzman9017]

@@raquelpurpleboxes you're correct I actually was going to say something about it just now, but I saw your comment. I know where he was going with it though. Still a good presentation. Honestly, my Microbiology professor Mr. Wallano, he should make a youtube video. He would kill it. He also makes it hilarious and super informative.

[@Hegeleze]

They now call the smaller space in many gram (+) bacteria a periplasmic space also, but still, really good lecture.

[@barbarabjorkman9796]

Excellent lecture! Thank you!

[@mroosie7488]

Very well explained

[@anapopovic899]

Super objasnjeno 😊

[@maureenk1635]

Great video. Thank you so much!

[@shanthala1345]

Thank you,

[@lingadurai9972]

It will be great if notes are made and uploaded in web

[@iffattahsin4086]

wow, grt explanation, thanks a lot😊

[@yulianieto1698]

great video, thank you!

[@ProfGillesBolduc]

Thank you!

[@alvinlawanto]

Does gram positive bacteria keep recycling their peptidoglican wall? If yes, what makes their wall ruptured (in natural environment) so that they have to make it over and over again? Thank you.

[@ProfGillesBolduc]

Great question. Think of the cell wall as being dynamic. It is constantly being broken down into its monomers and rebuilt into a strong outer structure. Instead of shedding its cell wall all at once like a lobster shedding (molting) its shell, a bacteria sends out enzymes to break a few covalent bonds holding NAG and NAM a little at a time and thus insert more disaacharides (NAG-NAM) to allow the cell to expand. This is important so that bacteria can grow and divide. We use this feature to our advantage when killing bacteria with betalactams, bacitracin, and vancomycin. These antibacterial agents prevent the linkage between sugars and weaken the cell wall, thus the bacteria dies.

[@alvinlawanto]

@@ProfGillesBolduc So can i say, bacteria grows bigger then devide into 2 smaller bacteria, etc. And bacteria has maximum size. Lucky they dont grow bigger and bigger. Hehe sorry for my weird point of view. Thanks for the answer. I'll come here again if i have another Q.

[@ProfGillesBolduc]

Yes. They grow until they reach a certain surface to volume ratio that can no longer support growth. Then they divide in half by binary fission into two small daughter cells. These in turn need to grow in size before they to can divide.

[@alvinlawanto]

@@ProfGillesBolduc and that is applied to all kind of bacteria? (Anaerob or aerob, gram negatif or positif)

[@ProfGillesBolduc]

Yes.

[@msmootoo]

thank you... very clear concept

[@mesnonasser5262]

19:50 what is the layer on top of the peptidoglycan and is it part of the envelope?

[@ProfGillesBolduc]

Only gram negative and acid fast cell walls have a layer above the peptidoglycan layer. In Gram negative cell walls it is the outer membrane. In Acid fast cell walls, it’s mycolic acid and other carbohydrates and lipids. Yes, these layers are part of the cell wall, which together with the cell membrane are the cell envelope. This is explained in more detail in the video.

[@mesnonasser5262]

@@ProfGillesBolduc thank you very much

[@mesnonasser5262]

@@ProfGillesBolduc is gram variable the same as acid fast?

[@ProfGillesBolduc]

No. Acid fast is specific to cells with mycolic acid. Gram variable occurs when gram standing old bacteria. Their cell walls break apart when old and releasing the crystal violet stain faster than normal and thus some cells appear pink while newer cells are purple.

[@EverythiNg-fg3wi]

But i thought tht these links are in the same layer I mean the four peptidic chaine of the first nam and the four peptidic chaine of the second name are connected using a pentapeptidic chain but in the same layer ! So how this 😭💔i really can't get it ! How are nams pf the same layer connected and how layers are connected

[@ProfGillesBolduc]

The connections are not just in the same layer, but also between different layers.

[@EverythiNg-fg3wi]

But how ? Plz tell me Or can u plz give me u'r fb account and i'll send u some of the pics i got 🙏🙏

[@ProfGillesBolduc]

@@EverythiNg-fg3wi I can only say that it makes sense that the pentapeptides extend in different planes so as to cross link with neighboring strands of peptidoglycan above, below and on either side so as to form a rigid cell wall layer. I have no proof to present you, as I did not visualize it, nor have I read it in detail in the literature.