Understanding Bacteria: Characteristics, Structure, and Function

okay so the topic of this video are some of the basic characteristics of bacteria so let's get started

well you might know that there's two big broad categories of cells the prokaryotes and the eukaryotes you know

when you look at this picture right here you can see wow the eukaryotes are just much larger well what are you carry oats

well these are cells that belong to Protista and fungus and plants and animals but our video today is focusing

on prokaryotic cells bacteria and then the group of called archaea now we're mainly focusing on the bacteria today

but bacteria and archaea are examples of prokaryotes so let's talk about them now so when we focus on the cell structure

of bacteria probably the most defining feature is that they're prokaryotes they lack a nucleus and other membrane-bound

organelles organelles that you might be familiar with if you studied cell parts they lack for instance a nucleus they

lack mitochondria they lack the rough and smooth er's they lacked Golgi bodies but what do they have then well they're

cells so they're gonna have genetic material they're gonna have a chromosome in what we call the nucleoid region now

it's all wound up you see in this picture right here it's not in the nucleus it's just kind of floating

around and like the middle of the cell in the area kind of called the nucleoid region they also have these other

segments of DNA called plasmids and these are ring shaped structures separate from the main chromosome that

has genes on them that they can actually transfer to one another we'll talk about that a little more detail in a moment

well another organelle they have our ribosomes ribosomes you might know our organelles that helped to create

proteins and here's a ribosome and as it's creating a protein it's actually gathering amino acids and linking them

into a chain here we have a bunch of amino acids being gathered and once that's finished the amino acids will

fall up and twist and fold and wrap into a protein that's a job performed by the ribosome to create proteins well we come

back to our diagram here notice they have a long whip-like tail on them called a flagellum the plural version

would be flagella so sometimes a bacteria will have a single flagellum sometimes they have multiple flagella

but when they whip their flagellum back and forth it propels them through their watery environment it's how they move

around notice going around the outside of the cell RVs short hair like extensions

called pili the singular version bean pillows and these things will actually help to attach and anchor the bacterium

on to whatever it is they're growing upon they also have another function which is kind of interesting now here's

their other function here's a bacterial cell and the process called conjugation where DNA segments of DNA can actually

be swapped and exchanged from bacterial cell to bacterial cell well here's a bacteria and in black is the main

chromosome floating around in the nucleoid region in red there's the plasmid and sticking out there's what's

called a sex pilis and watch what happens another bacterial cell will actually

combine and join with the bacteria on the left watch the red plasmid the plasmid is

duplicated and that plasmid will actually be transferred through the sex pillows into the neighbor on the right

and so when they disconnect you can see that conjugation is a way for bacteria to obtain advantageous genes and

segments of DNA from their neighbors that they can then use throughout the rest of their lives

okay so we'll come back to our diagram here now let's focus on their three outer layers to them starting with the

innermost the layer in green the plasma membrane this is the phospholipid bilayer you might know that it is

selectively permeable it allows molecules to pass in and out of the bacterial cell well the next layer in

gold is one of the defining features of a bacteria their cell wall a stiff layer that helps to maintain their shape made

from a combination of amino acids and sugars that we call peptidoglycan I say one of their defining features because

the cell wall is unique this type of cell wall is unique to bacteria you might know plants have a cell wall but

it's different from the bacterias fungus have a cell wall but it's different from bacteria so the cell wall

made of peptidoglycan is a pretty unique structure in bacteria well notice there's another outer layer called the

capsule the slimy outer coating recoding that actually helps the bacteria stick to surfaces and prevents it from drying

out so we actually see three outer layers to them the plasma membrane the cell wall and the capsule and it's worth

noting that even some bacteria can produce what's called an endoscope hoon to actually protect their DNA during

times of stress and harsh environments so in this situation here here's a bacterial cell being exposed to a high

amount of UV radiation on this case and no spore might begin to grow inside of the cell and actually cover and protect

the nucleoid region in the DNA of the bacterium now over time this bacterial cell could actually be destroyed but the

endospore protects the DNA inside and these things can last decades upon decades and let's say that over time the

environmental conditions change and and the area is not exposed to as much UV radiation anymore

well the endospore could kind of come out of this dormant stage and actually regrow into the bacterial cell so it can

continue on its existence it's a neat little adaptation that some bacteria have in order to protect themselves in

times of environmental stress okay let's gonna change directions here and talk about the various shapes of the

bacterial cells three basic shapes you have the rod-shaped bacteria bacillus is the singular version and Vasili is the

plural version and like the picture shows these are rod shaped cells then there are the spherically shaped cells

caucus is singular coxey's plural and then there are the spiral shaped bacterial cells the spur elemspur elem

is singular and forelli is plural and so when we combine these shapes with the next part so the next part being that

many bacteria grow in colonies and when you see prefixes in the name of a bacterium it actually gives you a lot of

information for example the prefix diplo means that the bacteria are found in pairs and this bacteria right here is

called a duplicitous bacteria well I hope you see why the word caucus is in its title you can see the spherical

shape diplo because there are two cells if you see the prefix strep doe in front of the name of a bacteria these are

bacteria that are found in Chains and so this example right here streptobacillus bacteria well you can see from the

picture the bacillus is in reference to that cells are rod-shaped strep though because there are chains of rod-shaped

bacteria cells and then there's the prefix staph a low which means grape-like

clusters so when you see for instance Staphylococcus bacteria well you can see why they're called caucus because

they're round and spherically shaped and staff low because they kind of look like cluster of grapes so when you see these

these prefixes it gives meaning to the bacteria the type of bacteria let's talk about how bacteria reproduce

while they reproduce asexually through a process called binary fission where one cell was split into two cells in my

animation here's a cell and you can see the round genetic material and the nucleoid region

notice how the DNA will a copy of the DNA is created as the cell goes through binary fission it'll start to enlarge

and the pieces of DNA are pulled to opposite ends and then right down the middle the cell begins to divide until

they are separated into two cells and so each of these cells are identical in their DNA

because in asexual reproduction you make clones exactly duplicate copies now this is a bit of a problem for them because

organisms that reproduce asexually tend to suffer from less genetic diversity after all their exact duplicates so if

something would harm the cell on the left chances are it would harm the cell on

the right but there's a neat little solution to this the solution is what we talked about briefly earlier called

conjugation in conjugation here's the main chromosome in the nucleoid region of our bacterial cell and in red here's

the plasmid and poking out to the right there's the sex pellets that we mentioned earlier so the cell on the

left is now going to connect to the cell on the right now watch the plasmid in red the plasmid is duplicated and one of

those copies is transferred through the sex palace into the neighbor on the right and so when they disconnect when

they separate you can see that the bacteria now have exchanged segments of DNA so is conjugation first of all it's

conjugation is it a form of reproduction and the answer is no but it's a solution to their problem the problem of having

less than genetic diversity conjugation solves that because they're able to obtain genetic diversity from their

neighbors by swapping and changing segments of their plasmids in their DNA like this

okay let's change direction here let's talk about how do they use oxygen and how do they make their energy how do

they perform respiration well here's three test tubes and each of them is filled with like a nutrient broth focus

on the test of on the Left let's put a cap on it now just beneath the cap you figure there's a little more oxygen at

the bottom of the test tube there's probably very little oxygen well over time what if a bunch of bacteria began

to grow just underneath the cap where there's more oxygen well these bacteria would probably be

called obligates aerobic bacteria they are obligated to live in oxygen and that's what the word aerobic means with

oxygen well why do they why do they or how do they use the oxygen they use the oxygen to make ATP the energy molecule

they actually perform cellular respiration now when you hear that you might think well wait a minute how do

they do that in order to do cellular respiration you need mitochondria bacteria don't have mitochondria and

that's correct but they are still able to perform cellular respiration because they have the necessary enzymes to do

cellular respiration in their cytoplasm and then their cell membrane so they're able to make ATP with oxygen and that's

why they're aerobic bacteria a good example of this bacteria are the bacteria that can cause tuberculosis

these are bacteria that will infect the person's lungs and of course living in your lungs they're exposed to lots of

oxygen well let's look at tuberculosis in a little more detail now if we look at this chest x-ray of a person's

healthy lungs here are the lungs right here blinking notice how the lungs appear just black

because after all they're filled with air and it doesn't really show up on an x-ray and no that's what a healthy chest

and healthy lungs would look like in an x-ray but in this picture here's a chest x-ray

of a tuberculosis patient see this cloudy area right here how come it's cloudy

well it's cloudy because it's filled with blood and pus and they're constantly coughing this up and it's a

sign that the person is quite ill because the bacterial infection that they have living inside of their lungs

the bacteria that causes the disease tuberculosis okay let's come back to our three test tubes and focus on the middle

test tube again let's add a cap so you figured just beneath the cap there's more oxygen versus at the bottom of the

test tube now what if bacteria begin to grow but they all tend to be concentrated near

the bottom of the testing where there's less oxygen well these bacteria would probably be

called obligate anaerobic bacteria they are obligated to not live in oxygen they can't survive the presence of oxygen so

what actually happens is in order to make their energy they performed fermentation they perform the anaerobic

cellular process called fermentation and that's how they make their energy in order to survive well you know here's

something maybe you've noticed at a grocery store have you ever picked up a can of food and and notice that the can

was swollen or puffy I hope not but if you have that's probably a sign of some anaerobic bacteria growing inside of the

can there's no oxygen in the can so if any bacteria are gonna grow in there they have to be anaerobic and because of

their actions they give off gases and it causes the can to swell and become puffy and so a swollen puffy can might be a

sign that there's anaerobic bacteria growing inside if you've ever heard of the type of food poisoning called

botulism it's a type of food poisoning caused by anaerobic bacteria so if you ever see swollen puffy cans don't buy

them you know report them to customer service at the grocery store and then move on but but don't buy them and eat

them okay let's come back to our three test tubes one last time the test tube on the

right let's add a lid so you figured just beneath the lid there's more oxygen verses at the bottom of the test tube

and over time what if bacteria began to grow and they grow all throughout the test tube although there's more bacteria

accumulating near the top where there is oxygen there are still some growing near the bottom where there's little if any

oxygen well these are the bacteria that are called the facultative anaerobic bacteria which means they can live with

or without oxygen if there's oxygen present they're able to do cellular respiration but if there's not oxygen

present then they perform fermentation in order to produce the energy that they need to survive so bacteria there's a

wide variety of ways in which bacteria can obtain their energy and survive okay so there you have it you want to

challenge yourself you know pause the video try to answer these questions and I've hope you found this video helpful

thanks for watching