Hello and welcome to bacteria learning. Goals for bacteria include understanding the differences between gram-positive and gram-negative bacteria.

You will appreciate how microbes take up substances from their environment and you will be familiar with components of cells.

You are having an overview of the metabolic capabilities of bacterial cells and perhaps most importantly you will have a newfound 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 here in Test. E Coli is a rod-shaped cell magnified about 100000 times.


Bacteria in contrast to the cells that make up eukaryotic cells bacteria have no nuclei and no membrane-bound organelles like mitochondria or chloroplasts.


They form spheres rod and spirals, so they look different under the microscope.

Remember they are found everywhere on Earth not just in you and on you but on every animal that exists in the oceans, the soils and even the skies. And remember the number of bacteria and earth is an impressive number 5 x 10 to the 30th number of every living thing on the planet.

Let’s take a look in more detail now at the structure of bacteria in the inside of every bacteria. There is a cytosol which is a fluid phase medium that contains a lot of the activity of the bacteria, the nucleic acid and 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 small pieces of DNA that often circular that is apart from the main chromosome of the bacteria surrounding this side cytosol is what we call a cell membrane and top of the cell membrane is typically a cell wall another structure and many bacteria. Have on the very outside what we call a capsule. And a very external part of the bacteria or some structures that help movement at one is called the fimbriae or pillow in the other is the flagellum. So that’s an overview of the bacterial cell in the various components.

Let’s take a look at some of these in detail.

First, let’s look at the cell membrane. This is a membrane that looks very much like the membrane that you may have and our cells are eukaryotic cell membranes. It’s made up of phospholipids phospholipid bilayer that has many proteins embedded in it and it functions by allowing the uptake of substrate molecules that the bacteria need by transporting 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 account just exist on its own and so has to be stabilized against detergent osmotic pressure and so forth are there two solutions that we recognize to this problem of protecting the cell membrane of bacteria and include gram-positive and gram-negative is there two ways of constructing The bacteria that are named after a Dutch microbiologist his name was Graham and he devised the stain to distinguish these two kinds of bacteria.


so we have gram-positive bacteria.

We have the cell membrane on the very inside of the bacterium surrounding the side of the sore and then on top of that is a thick layer called the peptidoglycan and this protects the between the peptidoglycan and the cell membrane is a space and we call this the periplasmic space so that’s the gram-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 at the outside which is called the outer membrane and so now we have to periplasmic spaces as opposed to the one in the gram-positive bacteria. There are a few other solutions for protecting that cell membrane, but we are going into them in our discussion. Now the gram stain differentiates gram-positive and gram-negative bacteria according to color gram-positive bacteria stain purple in the round bacteria that you can see in this image.

Where is gram-negative bacteria stain red and you can see the rod-like bacteria in this 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 gram-positive cocci include staphylococcus and streptococcus both causes of serious human infections.

Gram-negative include the Neisseria cocci, the cause agent of gonorrhea a sexually transmitted disease.


Gram-positive rods include the Clostridium and Corynebacterium bacteria that can cause many different diseases one of them is tetanus in the Corynebacterium can also cause diphtheria.



If only gram-negative rods include E coli a common inhabitant of our gut and salmonella both of these bacteria can cause gastrointestinal illness in humans.



You just completed your first article on Bacteria. The best exam preparation material brings the knowledge of worldwide leading medical experts to your PC tablet or smartphone. Prepare yourself and check your progress with our all articles.

Visit us again

Leave a Reply

Your email address will not be published. Required fields are marked *

Back to top