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Lecture Comments (12)

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Post by Luis Gallardo on November 29, 2015

Hi Dr. Eaton , first of all thanks for the awesome lecture! I have a question though, I was tought that prokaryotic and eukaryotic cells BOTH have cytoskeleton...I was even tought that the cytoskeleton was one of the 5 structures that supposedly ALL cells have (Genetic material, Cell membrane, Ribosomes, Cytosol and cytoskeleton). I googled around a bit and the internet confirmed that prokaryotic cells have cytoskeleton. So I was wondering why you said they didn't. Is it maybe because most prokaryotic cells don't have a cytoskeleton or something like that? I just wanna get that doubt out of my system. Thank you so much in advance! Best wishes.

1 answer

Last reply by: Dania Aljilani
Sun Jan 5, 2014 7:56 AM

Post by Dania Aljilani on January 5, 2014

Electron microscopes can also be used with alive specimen. You only mentioned TEM and SEM, but you didn't mention STM (Scanning Tunneling Microscope). In STM, the specimen in alive.

1 answer

Last reply by: Dr Carleen Eaton
Tue Aug 27, 2013 6:01 PM

Post by Mark Andrews on August 24, 2013

I was under the belief that the most supported view of the endosymbiotic theory is that an Archaea engulfed a Bacteria.  These are two different domains of life, not a bacteria consumed another bacteria.  

0 answers

Post by ysabella benavides on June 29, 2013

Why wont it let me watch "Comparisson of Prokaryotic and Eukaryotic cells"?

0 answers

Post by sushma penmetsa on May 1, 2013

The question about the solutions is reffering to the first part where it talks about the study of cells.

0 answers

Post by sushma penmetsa on May 1, 2013

Why are the solutions changing colors? Is there a reason or is it just for show? Another thing, how does the smaller anaerobe get inside the larger anaerobe? Thanks! This video was awesome!

2 answers

Last reply by: Raffles Zhu
Sun Jan 12, 2014 7:30 PM

Post by michelle daane on June 7, 2012

Didn't the larger aerobic bacteria engulf the smaller anaerobic? This would provide protection for the anaerobe.

0 answers

Post by Wongyu Jeong on February 22, 2011

i'm lovin' it

Cell Types (Prokaryotic and Eukaryotic)

  • Cell theory states that cells are the fundamental unit of structure and function of living organisms, that all organisms are composed of cells and that cells only arise from other cells.
  • Prokaryotes lack a nucleus and membrane bound organelles other than ribosomes. Their DNA is located in the nucleoid region and is circular in form.
  • Eukaryotic cells have various organelles that carry out specialized functions within the cells. Their genetic material is located in a membrane bound nucleus.
  • Both prokaryotic and eukaryotic cells have ribosomes; however, the ribosomes in bacterial cells are smaller than those in eukaryotic cells (70s versus 80s).
  • The endosymbiosis theory describes eukaryotic cells as arising from the engulfment of aerobic bacteria by larger, anaerobic bacteria.
  • Similarities between mitochondria and chloroplasts and bacterial cells provide support for the endosymbiosis theory.

Cell Types (Prokaryotic and Eukaryotic)

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Cell Theory and Cell Types 0:12
    • Cell Theory
    • Prokaryotic and Eukaryotic Cells
    • Endosymbiotic Theory
  • Study of Cells 4:07
    • Tools and Techniques
    • Light Microscopes
    • Light vs. Electron Microscopes: Magnification
    • Light vs. Electron Microscopes: Resolution
    • Light vs. Electron Microscopes: Specimens
    • Electron Microscopes: Transmission and Scanning
    • Cell Fractionation
    • Cell Fractionation Step 1: Homogenization
    • Cell Fractionation Step 2: Spin
    • Cell Fractionation Step 3: Differential Centrifugation
  • Comparison of Prokaryotic and Eukaryotic Cells 14:12
    • Prokaryotic vs. Eukaryotic Cells: Domains
    • Prokaryotic vs. Eukaryotic Cells: Plasma Membrane
    • Prokaryotic vs. Eukaryotic Cells: Cell Walls
    • Prokaryotic vs. Eukaryotic Cells: Genetic Materials
    • Prokaryotic vs. Eukaryotic Cells: Structures
    • Prokaryotic vs. Eukaryotic Cells: Unicellular and Multicellular
    • Prokaryotic vs. Eukaryotic Cells: Size
    • Plasmids
  • Prokaryotic vs. Eukaryotic Cells 19:22
    • Nucleus
    • Organelles
    • Cytoskeleton
    • Cell Wall
    • Ribosomes
    • Size
  • Comparison of Plant and Animal Cells 22:15
    • Plasma Membrane
    • Plant Cells Only: Cell Walls
    • Plant Cells Only: Central Vacuole
    • Animal Cells Only: Centrioles
    • Animal Cells Only: Lysosomes
  • Plant vs. Animal Cells 29:16
    • Overview of Plant and Animal Cells
  • Evidence for the Endosymbiotic Theory 30:52
    • Characteristics of Mitochondria and Chloroplasts
  • Example 1: Prokaryotic vs. Eukaryotic Cells 35:44
  • Example 2: Endosymbiotic Theory and Evidence 38:38
  • Example 3: Plant and Animal Cells 41:49
  • Example 4: Cell Fractionation 43:44

Transcription: Cell Types (Prokaryotic and Eukaryotic)

Welcome to Educator.com.0001

Today is a first in a series of lectures on cell structure and function.0002

And in this lecture, we are going to discuss the two major cell types: prokaryotic and eukaryotic cells.0007

We are going to begin by talking about cell theory, and cell theory states that cells are the fundamental unit of structure and function of living organisms.0014

All organisms are composed of cells, and cells only arise from other cells.0023

There are two major types of cells: prokaryotic cells and eukaryotic cells.0031

Prokaryotic cells are bacteria. Eukaryotic cells include plant cells, animal cells, protists, fungi.0036

Prokaryotic cells arose approximately 3.5 billion years ago, while eukaryotic cells arose more recently, 1.5 billion years ago.0062

The endosymbiotic theory is a theory that accounts for the origin of eukaryotic cells from a symbiotic relationship between two early prokaryotic cells.0073

Remember that symbiosis means a relationship between two organisms in which both organisms benefit.0090

The two organisms live closely together. They are interdependent and they each draw the benefit from the other.0097

Endo means within. This is a type of symbiosis that involves one cell living within another cell.0105

Early on, around 1.5 billion years ago, the environment greatly increased in the amount of oxygen.0112

And that created a crisis for anaerobic organisms because oxygen was actually toxic to them.0120

What is believed to have happened is that prokaryotic anaerobic bacteria engulfed smaller aerobic bacteria, so larger anaerobic bacteria engulfed smaller aerobic bacteria.0126

They each draw out the benefit.0156

The smaller bacteria received protection from the larger bacteria, and in turn, the smaller bacteria took care of the oxygen.0157

It actually used that oxygen to generate energy in the form of ATP.0168

Eventually, over time, this relationship evolved for the two organisms to become one, and what was originally just a larger bacteria, would be analogous to the eukaryotic cell.0174

And some of the organelles within the eukaryotic cell evolved from this smaller aerobic bacteria.0188

For example, mitochondria and chloroplast are organelles that have features that are similar to bacteria, and they provide proof for this theory.0195

And we will investigate those features more closely in a few minutes.0209

In particular, chloroplast are thought to have derived from the endocytosis of a photosynthetic bacteria called cyanobacteria or blue-green algae.0216

Blue-green algae is, sort of, a misnomer because these are actually are bacteria. They are photosynthetic bacteria.0233

And again, it is believed that chloroplast derived from these after the larger anaerobic bacteria engulfed them billions of years ago.0238

Before we go on to talk in more detail about the cell types, we are going to discuss some of the tools and the techniques used in the study of cells.0249

One of these is, of course, microscopes, and the microscope was invented in the 17th century.0258

Its use brought about great breakthroughs in biology because at last, we could see much more detailed structures than we could with just the naked eye.0263

Van Leeuwenhoek was an early inventor and developer of the microscope, and he was able to visualize microorganisms in a drop of water.0273

He also visualized cells such as red blood cells and sperm cells.0281

Robert Hooke described cells for the first time in a book in his book Micrographia that he wrote around 1665.0286

When you consider microscopes, there is two main types: light microscopes and electron microscopes.0299

Light microscopes are still widely used today, and they are the type of microscopes that Van Leeuwenhoek and Hooke used in their studies.0309

Both types of microscopes, electron and light, are described according to 2 features.0319

The first is magnification. Magnification tells you how much larger the specimen appears.0324

With a very high magnification, you could even go as high as a hundred thousand on electron microscope.0350

The higher the magnification, the larger an image appears, and the magnification could be as small as 2 times, 5 times or 5000 or even a 100,000 times.0355

With a light microscope, the maximum magnification only goes to about a thousand times,0368

whereas an electron microscope you can get a much higher magnification without the image becoming blurry.0374

OK, magnification is the first characteristic that we use to describe a microscope.0380

The second characteristic is resolution. Resolution does not have to do with the size of the image.0387

It has to do with the clarity of the image, and resolution is defined as the minimum distance at two points can be together, two points can be apart and still be distinguishable.0393

It is a minimum distance that two points can be a apart and still be distinguished as separate objects, so it has to do with the clarity.0407

If a microscope has a higher resolution, that means that you could see objects that are extremely close together, and they will not appear as one object.0416

They will actually appear separately as two objects, so the best microscope would have a very high magnification as well as a high resolution.0427

Resolution is determined by the wave length being used.0436

Light microscopes use light passing through the specimen, whereas, electron microscopes use a beam of electrons passing through a specimen.0439

An electron microscope is using something with a much shorter wave length, and actually shorter wave length equals higher resolution.0452

That is a big benefit of electron microscopes.0471

A disadvantage, though, is you can only use electron microscopes for dead specimens because the process to prepare the sample kills the cells.0474

They are only used for dead specimens, whereas with an electron microscope, you can use either a living or a dead specimen, which is a big advantage.0486

Now, electron microscopes come in two general types: transmission electron microscopes and scanning electron microscopes or SEM.0508

Transmission electron microscopes involve a preparation process for the sample in which thin sections are made and then visualized.0519

These are usually used to visualize the inside of the cell, to look at the inside of the cell,0529

whereas with scanning electron microscopes, we are generally looking at the surface of the cell or the outside.0537

With the scanning electron microscope, specimens are actually coated with a thin layer of gold and then observed.0548

Coating them or the fixative used for the specimens in transmission electron microscopy,0556

all of these procedures are going to kill an organism or a cell, which is why you can only use these for dead specimens.0562

Now, another difference between the two is that with TEM, the image looks very flat in two dimensional,0569

whereas with scanning electron microscopy the image looks...it has more depth, more 3-dimensional, 3-D appearing versus flat.0578

And that makes scanning electron microscopes very good to use with surfaces where you can see the depth of the different objects sitting on the surface of the cell.0591

Another method that is used is cell fractionation, and that is what this picture is right here; and there are actually several steps to cell fractionation.0601

The goal of cell fractionation is to separate out the different parts of the cell.0612

With a microscope, you may be looking at the whole cell. You may be focusing in on a part, but here, you can actually split up those parts and just study mitochondria if you would like.0616

There is 3 steps to cell fractionation. The first step is homogenization.0626

Homogenization involves putting a specimen like this, which is actually going to be cells, and they there in a liquid here; and you are going to put these in a blender.0643

You blend them up, but it is a type of blender and a type of procedure that is going to break apart the cells, which is going to release the organelles.0655

But it is not going to actually damage the organelles.0662

This creates homogeny, so right here, in this second tube, is the homogeny.0666

The homogeny is a suspension. It is a liquid with all these organelles and particles and pieces of the cells suspended in it.0677

The next step is to actually spin the homogeny.0684

When you spin the homogeny, what is going to happen are the heaviest particles are going to sink to the bottom and form what is called a pellet.0689

At the top, are going to be lighter particles in a solution, and this is called the supernatant.0696

The supernatant is the fluid on top. The pellet is the solid part at the bottom.0702

The next step is differential centrifugation.0713

A very high speed centrifuge called an alter centrifuge is used, and you pour the supernatant into a new tube, spin at a higher speed than you used from the first time you spun.0720

What that is going to do is allow particles that were too light to be forced to the bottom, in that original spin to be forced to the bottom the second time.0733

You create another pellet and another set of supernatant. Pour the supernatant off into another tube.0743

Repeat the procedure, and you do this differential centrifugation until you have the pellet that you want.0748

In the beginning, the pellets are going to contain heavier parts of the cells. By the end, you are going to have very light parts such as the mitochondria or the ribosomes.0755

Then, scientists can take whichever pellet they are interested in, look at this particular organelles without having the rest of the cell right there.0770

Again, the goal of cell fractionation is to separate out the cell into different sections, different organelles.0779

And that is done by weight and by spinning them, and it differentiates each of these organelles and particles by weight.0787

Finally, cell fractionation, cell fractionation is a method of preparing a sample to use for transmission electron microscopy.0795

In this, the cells are frozen in liquid nitrogen, and it creates a block; and then, you fracture or split that block, and it is splits right between the plasma membrane.0805

The plasma membrane has two airs. You can think of it as being like an Oreo cookie, and when you split it, it would split apart in the middle.0815

It splits right along the line of the plasma membrane.0824

Next, that specimen that has been split is coated with gold or platinum, some type of metal, as well as a layer of carbon, and the specimen, itself, is digested away.0828

Freeze fracture leaves you with a cast of the specimen, and you can, then, look at that specimen via transmission electron microscopy.0839

Now that we have talked about methods used to study cells, we are going to go on to compare the two major cell types: eukaryotic and prokaryotic.0852

Here, we have a prokaryotic cell. This is a typical bacterial cell.0860

For the eukaryotic cell, I have used a sketch of an animal cell.0866

This is a eukaryotic cell, but it is going to be a little bit different than, let's say, a plant cell, which we are going to look at in a moment.0871

We are just going to be talking about the general differences between prokaryotic cells and eukaryotic cells.0877

Eukaryotes are found in the domain eukarya, whereas prokaryotic cells include the other domains.0884

And remember that in the three domain system, there is domain bacteria, domain archaea, and so we will say domain bacteria and archaea.0901

And then, domain eukarya includes plants, animals, fungi, protists.0916

So, prokaryotic cells, these two domains, eukaryotic cells just include one domain, but it is a very large domain- the domain eukarya.0923

Starting up by looking at the prokaryotic cell, you can see that it is much simpler in construction than the eukaryotic cell.0933

Both prokaryotes and eukaryotes have a plasma membrane. This is also called the cell membrane, and it is composed of a phospholipid bilayer.0940

In the prokaryotic cell, the plasma membrane is right here, and in both of these, the plasma membrane is composed of phospholipid bilayer.0956

In addition, bacterial cells have a cell wall.0975

Animal cells do not have cell walls. However, fungi and plants do have cell walls.0982

Some eukaryotes have cell walls. Animal cells do not have cell walls.0989

The next thing to look at is where the genetic material of the cell resides.0998

In prokaryotes, there is no true nucleus. Instead, what you have is called a nucleoid region.1003

This is the nucleoid region. The DNA is found here, and a DNA is circular.1011

It is not organized into chromosomes, and it is not bound by proteins the way eukaryotic DNA is.1017

Here, there is a true nucleus. This nucleus is bound by a double membrane, and inside the nucleus are chromosomes.1024

These chromosomes are bound by proteins called histones, so chromosomes, and they are bound by proteins called histones- chromosomes with histones.1035

The other thing you will notice is that there are a lot more structures inside the eukaryotic cell, and these structures are called organelles.1048

And we are going to talk in detail in the next section on subcellular structure about each of these organelles.1057

But for now, just to name a few, these are the mitochondria, the endoplasmic reticulum, the Golgi apparatus, ribosomes.1064

Eukaryotic cells have membrane-bound organelles that carry out specialized functions. Prokaryotic cells only have ribosomes.1074

Both prokaryotic and eukaryotic cells have ribosomes. Prokaryotic cells are lacking the other organelles, so ribosomes here, and that is it for organelles in a prokaryotic cell.1084

Another differences between prokaryotes and eukaryotes is that prokaryotes are mainly unicellular, while eukaryotes like plants and animals are very complex multicellular organisms.1099

Prokaryotes also are smaller.1113

They are about ten to a hundred times smaller than a typical eukaryotic cell about 1 to 10 micrometers, whereas a eukaryotic cell will be in the range of, say, 10 to 500 micrometers.1115

In addition to the nucleoid region where most of the genetic material is, bacteria have structures called plasmids, and these are rings of DNA that contain just a few extra genes.1132

Most of these are not essential for survival. They often just help the bacterial cell to be more virulent, but this is another feature that prokaryotic cells have that eukaryotic cells do not.1144

Alright, so we have talked about a bunch of differences and similarities between prokaryotic and eukaryotic cells.1156

Now, to summarize those, nucleus: prokaryotic cells do not have a true nucleus. Instead, they have circular DNA in the nucleoid region.1162

You will sometimes hear this referred to as naked DNA, and that means that there is no proteins bound to the DNA.1171

In contrast, eukaryotic cells have DNA organized into chromosomes. They are bound by histone protein, and they are contained within a membrane bound nucleus.1177

Organelles: prokaryotes lack membrane-bound organelles except for ribosomes - they do have ribosomes -1189

whereas, eukaryotic cells have many membrane-bound organelles that carry out specialized functions within the cell.1196

Cytoskeleton: since eukaryotic cells have a much more complex structure, in order to organize that structure,1203

they have a system of microtubules and microfilaments that organize the cell via what is called a cytoskeleton.1210

And we will talk about that under subcellular structure, but for right now, just know that the cytoskeleton helps the cell to maintain its shape.1218

It provides some protection. It provides organization.1226

It provides motility, whereas prokaryotic cells lack a cytoskeleton.1229

Cell wall: bacteria have cell walls, and these contain peptidoglycan.1235

There are no cell walls in animals. Plants have cell walls composed of cellulose.1243

Fungi have cell walls that contain chitin, and some protists have cell walls that are made of materials such as polysaccharides.1250

Ribosomes: both prokaryotes and eukaryotes have ribosomes, but they are different in structure.1257

Prokaryotes have smaller ribosomes, and you will see this S here, and it has to do with the sedimentation.1264

Remember we talked about in fractionation that certain particles or organelles sediment to the bottom.1270

They form a pellet, and that depends on how heavy the particular item is.1277

Smaller ribosomes are found in prokaryotes, and those are 70S, as far as their sedimentation, whereas eukaryotic ribosomes are different in structure.1283

They are larger. They are actually 80S.1293

Size: prokaryotic cells are much smaller than a typical eukaryotic cell, which is larger.1298

And then, looking at it as a whole, not just as individual cell, prokaryotic cells are usually unicellular, whereas eukaryotic organisms are multicellular.1304

Prokaryotes are just one-celled organism, whereas eukaryotes, plants, animals, very complex multicellular organisms that have different tissue types to carry out special functions.1316

The cells, themselves, become specialized.1330

We compared prokaryotic and eukaryotic cells. Now, we are going to compare plant and animal cells.1336

Remember that these are both eukaryotic cells, so they are going to have many features that are actually the same, but there is very important differences too.1341

And one of the central tenants of biology is that form follows function.1351

This means that the plant cell is going to have some structures - so that is form - that will carry out specialized functions, for example photosynthesis.1358

Animal cells do not carry out photosynthesis. They do not need structures that are going to achieve photosynthesis.1369

Looking at these two in general, they both have a plasma membrane or cell membrane.1375

Taking a look at plant cells, they also have a cell wall. Bacterial cells have cell walls.1393

Plant cells have cell walls, but in bacterial cells, the cell wall contains peptidoglycan, whereas in plant cells, cell walls contain cellulose. In fact, plant cells can actually have two cell walls.1401

They all have what is called a primary cell wall, and that contains cellulose, which is a polysaccharide.1415

However, between the plasma membrane and this primary cell wall, can be a secondary cell wall, so right in here, there might be another cell wall.1426

And this secondary cell wall contains cellulose, but it also contains lignin; and lignin is a polymer that gives additional strength to the plant.1440

For example, wood contains a lot of lignin, and because they do not have skeletons, plants need these cell walls to give them more strength and help them maintain their shape.1453

In addition, the cell wall prevents the plant cell from bursting in a hypotonic environment.1469

As we will discuss, when we talk about plasma membranes, when a cell is an environment where there are less solutes in the solution than there are within the cell,1477

then, water is going to enter the cell, and that can actually cause a cell to burst. However, if it has a cell wall, it protects it from bursting.1490

The cell wall, in fact, helps the plant cell to maintain turgor or rigidity because what happens is, this structure, which is called a central vacuole,1500

is something that is not found in animal cells, and water can be stored here as well as food; and it takes care of waste, but one of the functions of a central vacuole is it contains water.1514

And as a central vacuole becomes large, it can push on the cell wall; and that will make the plant rigid.1527

Instead of wilting, the plant will stand up. The stem of the plant will be rigid, its leaves, and that is through something called turgor.1534

The central vacuole and the cell wall allow for turgor, which is pressure due to water pushing against this firm cell wall, and it allows the plant to maintain its shape and be rigid instead of just limp.1544

OK, no central vacuole in animal cells. No cell wall in plant cells, excuse me, in animal cells, so cell wall, central vacuole in the plant cell.1560

Here in the animal cell, there is no cell wall, and there is no central vacuole, so this is the plant cell.1575

As you can see, a lot of the structures are similar because since they are eukaryotes, they both have a nucleus. It is membrane-bound.1586

You can see the mitochondria, endoplasmic reticulum and various other structures.1593

In addition, animal cells have structures called centrioles. Centrioles are regions that help to organize the cytoskeleton.1600

They are found within centrosomes, and they play a key role in organizing what is called the spindle apparatus1613

that helps to separate out the chromosomes during miosis and mitosis so that the daughter cells get equal numbers of chromosomes.1623

Centrioles are a type of microtubule-organizing centers that are lacking in plant cells.1631

Plant cells do not have centrioles. They do not have centrosomes, but they do have organized microtubules.1637

They have just a different type of microtubule-organizing center.1643

Plant cells, let's see, plants have no centrioles. They also have no lysosomes.1652

Lysosomes are small sacks that contain enzymes separate down old organelles.1667

Also, if there is an invader that a cell from the immune system has engulfed such as a bacteria, lysosomes can break down those invaders.1684

Lysosomes play a role in ridding the cell of things that are harmful or things that it does not need any longer such as old organelles.1694

Although, the component parts of the old organelles are actually reused to make new organelles.1703

Lysosomes are not found in plant cells, so no centrioles, no lysosomes. Plants are lacking those, but plants have a few things that animal cells do not.1708

We mentioned the cell wall. I also mentioned the central vacuole, and another important part is chloroplast.1720

Chloroplast are organelles that are specialized to carry out photosynthesis.1731

And again, we are going to go into a detail of all these structures in the next section, but just to give you an overview, the major function of chloroplast is to carry out photosynthesis.1734

In addition, they contain green pigment, and that is why the stems and the leaves of plants appear green because of this green pigment inside chloroplast.1745

To sum up, it is important that you know the differences between plant and animal cells because comparisons are important on the test.1756

OK, cell walls: animal cells do not have cell walls. Plant cells have primary cell walls containing cellulose.1764

Some plant cells actually have a secondary cell wall, which contains both cellulose and lignin.1773

Lysosomes: lysosomes are present in animal cells. There are no lysosomes in plant cells.1783

And again, these are sacs that contain digestive enzymes that break down old organelles and also pathogens.1790

Chloroplast: animal cells do not have chloroplast, plant cells do. These are the site of photosynthesis.1798

Centrioles: these are present in animal cells, not in plant cells, but plant cells do have MTOCs which are microtubule-organizing centers.1806

Centrioles help to organize microtubules, whereas that role is taken on by different structures on the plant cell, although, those have not been well-described.1823

Central vacuole: this is not present in animal cells. Animal cells can have vacuoles, but they do not have that large central vacuole.1836

In the plants, these play a role in storage, waste disposal, maintenance of pH in the cells. They are very important structures .1844

In the beginning of this lesson, I mentioned the endosymbiotic theory.1855

And I said that certain characteristics of eukaryotic cells, particularly the mitochondria and chloroplast provides support for this theory.1859

Let’s look at exactly what those characteristics are.1869

First, they have circular DNA. Bacterial cells have circular DNA, whereas eukaryotic cells have DNA organized into chromosomes.1874

The fact that mitochondria and chloroplast have circular DNA, is the similarity to prokaryotic cells.1892

And that provides evidence for the fact that these may have actually descended from prokaryotic cells that were engulfed by other larger anaerobic prokaryotic cells.1899

This DNA is, again, not in chromosome form, and they lack histones, which are the protein that DNA found in chromosomes is bound to.1914

This DNA looks a lot more like bacterial DNA in structure, in organization, rather than looking like eukaryotic organization of DNA.1928

Another feature of mitochondria and chloroplast is that they have a double membrane.1941

And if you think about the endosymbiotic theory, it makes sense that organelles derived from the internal cell, the cell that was engulfed, would have a double membrane.1949

If you have a larger bacterial cell, and it has a cell membrane, and then, you have a smaller aerobic bacterial cell, and this cell, the smaller cell, ends up engulfed by the larger cell,1961

what is going to happen is you are going to end up with the larger cell, with this cell membrane around it, and then, the smaller cell inside with its original membrane.1986

But as it pushed its way in or was engulfed actually, the membrane from the larger cell wrapped around that smaller cell.2004

This actually engulfed it, and it pinched off; and formed an outer membrane around the original membrane of that smaller bacterial cell.2018

The double membrane found in both mitochondria and chloroplast likely originated from the original membrane of the smaller cell and the membrane of the larger cell that engulfed that smaller cell.2029

The third aspect of mitochondria and chloroplast that provide evidence for the endosymbiotic theory are the fact that both these two organelles2044

have their own ribosomes separate from those of the rest of the cell, and they are the same size as bacterial ribosomes.2056

Recall that eukaryotic ribosomes are 80S. Here, prokaryotic ribosomes are 70S, and mitochondria and chloroplast ribosomes are 70S as well, so another similarity to bacterial cells.2068

Bacteria divide through a method called binary fission, where they split into two daughter cells. Chloroplast and mitochondria also undergo binary fission.2085

Mitochondria arise only from other mitochondria to binary fission, and chloroplast arise only from other chloroplast.2100

Size: mitochondria and chloroplast are the size of the typical bacteria.2111

These five elements, the fact that both organelles have circular DNA like bacteria, they have 70S ribosomes like bacteria. They are the size of bacteria.2119

They undergo binary fission, and they have a double membrane that probably originated from when they were engulfed.2131

These five points, all provide support for the endosymbiotic theory of eukaryotic cell origin.2136

Now, we are going to go through a few examples. First, list four differences between prokaryotic and eukaryotic cells.2145

First difference: prokaryotes- no nucleus and the DNA is circular.2154

Eukaryotes- they have a nucleus. The DNA is found within the nucleus of the cell, and the DNA is organized as chromosomes.2168

The DNA is also bound to histones, so difference in the location and the organization of the DNA.2188

Second difference: prokaryotes lack membrane-bound organelles, except, they do have ribosomes, so that is an important exemption.2204

Eukaryotic cells have numerous organelles bound by membranes, which carry out specialized functions within the cell.2224

Prokaryotic cells lack a cytoskeleton, whereas eukaryotic cells have a cytoskeleton that helps to organize the organelles within the cell.2237

It provides the shape and structure for the cell and also allows for motility.2257

Prokaryotic cells have smaller ribosomes. They have 70S ribosomes, whereas eukaryotic cells have larger ribosomes.2266

They are 80S ribosomes.2277

I listed four here as the question asked, but there is certainly others that you could point out.2282

Prokaryotic cells are smaller, so you could have discussed smaller versus larger eukaryotic cells.2289

You could have mentioned the fact that prokaryotic cells have plasmids. Those are extra pieces of DNA that contain a few genes, and they are outside the nucleoid region.2299

This asked for four, but there are certainly other differences that you could have listed.2313

Example 2: describe the endosymbiotic theory of the origin of eukaryotic cells. Give two pieces of evidence in support of the theory.2321

OK, endosymbiotic theory, the endosymbiotic theory states that eukaryotic cells arose from engulfment of smaller aerobic prokaryotic cells by larger anaerobic prokaryotic cells.2330

Remember, symbiosis means the two organisms live closely with one another, and they each benefit from the relationship.2374

Endosymbiosis means that one organism actually lives within the other organism.2383

One cell engulfed the other. They have become more and more interdependent.2389

Through time, through evolution, what was once independent prokaryotic cell living within the larger cell became organelles.2392

Two pieces of evidence: well, the evidence has to do with the similarity of mitochondria and chloroplast which are organelles, similarity between those and bacteria or prokaryotic cells.2400

One piece of evidence is mitochondria and chloroplast have their own DNA and it is circular. This is similar to that of bacterial cells.2413

Mitochondria and chloroplast also have double membranes.2433

These double membranes may have originated from when the larger bacterial cell engulfed the smaller bacterial cell.2444

and the membrane of the larger cell became the outer membrane of that smaller cell, which also retains its own membrane, which is, then, the inner membrane of the mitochondria and chloroplast.2454

This only asked for two. There are certainly other pieces of evidence.2470

Size: mitochondria and chloroplast are similar in size to bacterial cells. The ribosomes of mitochondria and chloroplast are 70S like that of bacterial cells.2474

They divide through binary fission. Both bacterial cells and mitochondria and chloroplast divide through binary fission.2489

These are all pieces of evidence in support of the endosymbiotic theory.2504

Example three: state three differences between plant and animal cells.2511

I am going to go ahead and write animal cells up here and plant cells up here and then, put what occurs for each.2516

Cell walls: animal cells have no cell walls. Plant cells have cell walls, which contain cellulose.2526

They may also have a secondary cell wall - and I will put this in parenthesis cause it is sometimes - containing lignin. This is the primary cell wall.2537

Secondary cell wall contains both cellulose and lignin.2551

Animal cells have lysosomes- plant cells do not.2554

And remember that lysosomes contain enzymes that breakdown old organelles or pathogens or whatever a cell needs to destroy.2563

In addition, animal cells have centrioles. These organize the microtubules particularly during miosis and mitosis- plant cells do not.2572

Although, they do have microtubule-organizing centers- MTOCs.2584

So, that is three differences. Another big difference is that plant cells have chloroplasts, which are the site of photosynthesis- animal cells do not.2592

Plants also have a large central vacuole, which carries out multiple functions such as storage of water and removal of waste products- animal cells do not.2606

Three differences for the question, and there is a couple more major ones, as well.2620

Example 4: describe the process of cell fractionation. OK, cell fractionation has three steps.2626

The first is homogenization. In this step, the cells are broken apart, but it is done in such a way that the organelles are not damaged.2634

The second step is to spin the homogeny. The homogony is a liquid that contains the various parts of the cells in it.2649

Spinning the homogeny is going to result in a pellet at the bottom tube and a supernatant suspended on top.2660

The supernatant is poured off. Spin the homogeny, and then, pour off the supernatant into another tube.2669

Spin that too. Pour off that supernatant.2682

Spin that too, and keep going at faster and faster speeds to separate out lighter and lighter organelles.2687

This is called, this process of pouring off the supernatant, spinning it, pouring it off, raising the speed, is called differential centrifugation.2691

And it allows you to separate out these parts of the cell by which pellets they sediments into.2705

Why is it useful in the study of cells? Well, cell fractionation separates organelles into different pellets.2712

The early pellets, those are ones that were spun in the tube that was spun at a lower speed. Those are going to be heavier items.2726

The later pellets, the ones that were spun very fast in order to get them to sediment, are very light. They are things like mitochondria and ribosomes.2734

That concludes this section of Educator.com, our discussion of the differences between the major cell types.2742

See you again soon.2749