Understanding Bacteria: Gram Positive vs. Gram Negative

[Music] hello and welcome to bacteria my learning goals for bacteria

include you'll understand the differences between gr positive and gram negative bacteria you'll appreciate how

microbes take up substances from their environment you'll be familiar with components of bacterial cells you'll

have an overview of the metabolic capabilities of bacterial cells and perhaps most importantly you'll have a

new found appreciation for all that bacteria can do let's start with a little review of what we know about

bacteria here's an electron micrograph of a common bacterium from your intestine eoli these are rod-shaped

cells and they're magnified about 100,000 times bacteria IIA in contrast to the

cells that make us up eukaryotic cells bacteria have no nuclei and no membranebound organel like mitochondria

or chloroplasts they form spheres rods and spirals so they look differently under

the microscope and remember they're found everywhere on Earth not just in you and

on you but on every animal that exists and the oceans the soils and even the skies and remember the number of

bacteria on Earth is an impressive number 5 * 10 to the 30th they now number every living thing on the

planet so let's take a look in more detail now at the structure of bacteria in the inside of every bacterial cell is

the cytool which is a fluid phase medium that contains a lot of the activity of

the bacteria the nucleic acid the DNA of a bacteria is present in a structure called the

nucleoid the cytoplasm of bacteria also contains ribosomes these are the places where protein synthesis occurs and many

bacteria have plasmids these are small pieces of DNA they're often circular that are apart from the main chromosome

of the bacteria surrounding this cytool is what we call a cell

membrane on top of the cell membrane there's typically a cell wall another structure and many bacteria have on the

very outside what we call a capsule on the very external part of the bacteria are some structures that help

movement one is called the fmri or pilli and the other is the flagellum so that's an overview view of

the bacterial cell and the various components let's take a look at some of these in some

detail first let's look at the cell membrane this is a membrane that looks very much like the membrane that you or

I may have on our cells a eukaryotic cell membrane it's made up of phospholipids it's a phospholipid

bilayer it has many proteins embedded in it and it functions by allowing the uptake of substrates mole fuls that the

bacterium needs by specific transport proteins now this is a very fragile membrane because bacteria are typically

exposed to either cellular fluids or to the environment the cell membrane has to have more protection it can't just exist

on its own and so it has to be stabilized against detergents osmotic pressure and so

forth there are two solutions that we recognize to this problem of protecting the cell membrane of bacteria and they

include gram positive and gram negative these are two ways of constructing the outside of the bacteria that are named

after a Dutch microbiologist his name was Graham and he devised a stain to distinguish these two kinds of

bacteria so we have gr positive bacteria we have the cell membrane on the very inside of the bacterium surrounding the

cytool and then on top of that is a thick layer called the pep pep glycan and this protects the Cell between the

peptidoglycan and the cell membrane is a space and we call this the periplasmic space so that's the gr positive

solution there is a gram negative solution where the cell membrane is covered with a thin layer of

peptidoglycan and then there is a second membrane on the outside which is called the outer

membrane and so now we have two periplasmic spaces as opposed to the one in the gr positive bacteria there are a

few other solutions for protecting that cell membrane but we won't be going into them in our discussion now the Gram

stain differentiates gr positive and gram negative bacteria according to color gr positive bacteria stained

purple and these are the round bacteria that you can see in this image whereas gram negative bacteria stain red and you

can see they're rodlike bacteria in this IM image a few examples of different kinds

of bacteria based on the Gram stain in the morphology will help you put these into context so gr positive coxy

includes staf coccus and streptococus these are both causes of serious human infections gram negative coxy include

the neria these are the causative agents of ganara a sexually transmitted disease gr positive rods include the clostridia

and the corini bacteria the clostridia can cause many different diseases one of them is tetanus and the corini bacteria

uh can also cause diptheria and finally gram negative rods include eoli a common inhabitant of our

gut and salmonella both of these bacteria can cause gastrointestinal illness in humans you just completed

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