A Tour of the Cell

Summary

In this educational podcast, Mr. Andersen offers an insightful tour of the cell, explaining why cells are small for efficient diffusion, their complex internal structures like the cytoskeleton, and the importance of microscopes in cell study. He distinguishes between prokaryotic and eukaryotic cells, detailing the functions of various organelles in eukaryotic cells, such as the nucleus, ribosomes, and mitochondria. The podcast aims to demystify the cell's complexity and encourage deeper learning through interactive review.

Takeaways

• 🔬 Cells are small to facilitate efficient diffusion, which is the process by which materials move in and out of cells.
• 🌟 The size of a cell is also determined by the need to house its genetic material and machinery without being infinitely small.
• 🏗️ Cells are complex structures with a cytoskeleton that supports organelles and allows for the movement of materials via motor proteins.
• 🔬 The invention of microscopes, both optical and electron, was crucial for scientists to observe and study cells, which are too small to see with the naked eye.
• 🌌 Optical microscopes use light and lenses for magnification, while electron microscopes use magnets to focus electrons and provide higher magnification.
• 🌈 Fluorescent dyes in optical microscopes and electron microscopes have improved the visualization of living cells and their structures.
• 🔴 There are two major types of cells: prokaryotic cells, which lack a nucleus, and eukaryotic cells, which contain a nucleus and other organelles.
• 🧬 All cells, regardless of type, possess genetic material in the form of DNA, a cell membrane, cytosol, and ribosomes.
• 🌿 Eukaryotic cells have additional organelles like mitochondria, which are involved in energy production, and are found in larger organisms such as plants and animals.
• 🔝 The nucleus is often considered the control center of the cell, housing the cell's DNA and regulating protein and enzyme production.
• 🛠️ Ribosomes, both in prokaryotic and eukaryotic cells, are essential for protein synthesis, using messenger RNA as a template.

Q & A

Why are cells small?

Cells are small because material moves into and out of a cell through diffusion. A smaller size ensures a shorter distance for materials to travel, making the process more efficient.

What role does the cytoskeleton play in a cell?

The cytoskeleton provides structural support, maintains the cell's shape, and facilitates movement and transport within the cell using motor proteins.

What are the two major types of cells?

The two major types of cells are prokaryotic cells, which lack a nucleus, and eukaryotic cells, which have a nucleus.

How do optical microscopes differ from electron microscopes?

Optical microscopes use light and lenses to magnify images, while electron microscopes use magnets to focus electrons, allowing for much higher magnification and resolution.

What is the function of the nucleus in a cell?

The nucleus contains the cell's genetic material (DNA) and controls the cell's activities by regulating gene expression and protein synthesis.

What are ribosomes responsible for?

Ribosomes are responsible for protein synthesis, assembling proteins by translating messenger RNA (mRNA) into amino acid sequences.

What is the difference between rough ER and smooth ER?

Rough ER has ribosomes on its surface and is involved in protein synthesis and membrane production, while smooth ER lacks ribosomes and is involved in lipid synthesis and detoxification.

What is the role of the Golgi apparatus?

The Golgi apparatus modifies, sorts, and packages proteins and lipids for transport to different destinations within or outside the cell.

How do mitochondria generate energy for the cell?

Mitochondria generate energy in the form of ATP through cellular respiration. They have a double membrane and their own DNA, supporting the endosymbiotic theory of their origin.

What is the function of lysosomes in a cell?

Lysosomes contain digestive enzymes that break down waste materials and cellular debris. They can also trigger apoptosis by releasing these enzymes to dissolve the cell.

Outlines

00:00

🌐 Cell Size and Structure

In this paragraph, Mr. Andersen introduces the concept of cell size and its significance in cellular function. He explains that cells are small to facilitate efficient diffusion of materials, which would be slow in larger volumes. The increased surface area relative to volume aids in this process. He also touches on the idea that cells are not simply bags of jelly but complex entities with a cytoskeleton that supports organelles and facilitates their movement via motor proteins. The paragraph concludes with a brief history of cell observation, highlighting the importance of microscopes in advancing our understanding of cellular structures.

05:03

🔬 Microscopes and Cell Types

This section delves into the types of microscopes used to observe cells, distinguishing between optical and electron microscopes. Optical microscopes use light and lenses for magnification, while electron microscopes employ magnets to focus electrons, offering higher magnification and resolution. The paragraph also discusses the limitations of electron microscopy, such as the need to coat samples with a thin layer of metal and the destructive nature of the process on living organisms. The narrative then shifts to the classification of cells, highlighting the differences between prokaryotic and eukaryotic cells, and briefly describes their characteristics and similarities.

10:07

🌿 Eukaryotic Cells and Their Organelles

The focus of this paragraph is on eukaryotic cells, which are more complex than prokaryotic cells due to the presence of a nucleus and various organelles. The narrator provides a detailed tour of a eukaryotic cell, starting with the nucleolus, where ribosomes are assembled, and moving through other organelles such as the nucleus, ribosomes, vesicles, rough ER, Golgi apparatus, cytoskeleton, smooth ER, mitochondria, vacuole, cytosol, lysosome, and centriole. Each organelle's function and role within the cell is discussed, providing a comprehensive overview of the cell's internal machinery and its importance in maintaining life processes.

Keywords

💡Diffusion

Diffusion is the process by which molecules move from an area of higher concentration to an area of lower concentration until equilibrium is reached. In the context of the video, it is highlighted as the reason why cells are small, as larger cells would have a reduced surface area to volume ratio, slowing down the diffusion of materials like oxygen and carbon dioxide in and out of the cell.

💡Cytoskeleton

The cytoskeleton is a network of protein fibers that provide structural support and facilitate movement within the cell. It is likened to a lattice inside the cell, with organelles fitting within this structure. The script emphasizes the cytoskeleton's role in cell complexity and its function as a transport system for materials, using motor proteins that 'walk' along the cytoskeleton.

💡Microscope

A microscope is an instrument that magnifies objects to a size visible to the naked eye. The video script discusses two types: optical microscopes, which use light and lenses, and electron microscopes, which use magnets to focus electrons. The development of microscopes was crucial for the study of cells, as they allowed scientists to visualize these previously invisible structures.

💡Prokaryotic Cells

Prokaryotic cells are a type of cell that lacks a nucleus and membrane-bound organelles. The script mentions that bacteria and archaea are examples of prokaryotic cells. These cells are simpler in structure compared to eukaryotic cells and are significant in understanding the basic unit of life and its evolution.

💡Eukaryotic Cells

Eukaryotic cells are cells that contain a nucleus and other membrane-bound organelles. The script explains that eukaryotic cells are found in organisms that are not microscopic, such as plants, animals, fungi, and protists. They are more complex than prokaryotic cells and are central to the video's exploration of cell structure and function.

💡Nucleus

The nucleus is a double-membrane bound organelle found in eukaryotic cells that houses the cell's genetic material, or DNA. The script describes the nucleus as the control center of the cell, where the genetic material dictates the cell's function and development. It also discusses the nuclear pores that allow for the movement of materials in and out of the nucleus.

💡Ribosome

Ribosomes are the cellular structures responsible for protein synthesis. The script describes them as having two subunits, with messenger RNA moving through the structure to facilitate the construction of proteins. Ribosomes are essential for life, as they are the sites where the genetic code is translated into functional proteins.

💡Endoplasmic Reticulum (ER)

The endoplasmic reticulum is a network of membranes that plays a crucial role in the synthesis of proteins and lipids. The script distinguishes between the rough ER, which is studded with ribosomes and involved in protein synthesis, and the smooth ER, which lacks ribosomes and is involved in lipid synthesis and detoxification.

💡Golgi Apparatus

The Golgi apparatus is an organelle that modifies, sorts, and packages proteins and lipids for secretion or use within the cell. The script likens it to a 'shipping' department, receiving materials in vesicles, modifying them, and then sending them to their appropriate destinations within the cell.

💡Mitochondria

Mitochondria are known as the 'powerhouses' of the cell, generating energy in the form of ATP through cellular respiration. The script discusses their unique structure, which includes a folded membrane, and their evolutionary origin through endosymbiosis, where they are thought to have been incorporated into eukaryotic cells from bacteria.

💡Cytosol

Cytosol refers to the fluid within the cell that surrounds the organelles and in which they are suspended. The script mentions that the cytosol is not just a simple fluid but contains concentration gradients and solutes, indicating that it is a complex and integral part of the cell's internal environment.

Highlights

Cells are small to facilitate efficient material diffusion and maintain a suitable surface area to volume ratio.

Cells are not merely bags of jelly but possess a complex cytoskeleton made of various macromolecules.

The cytoskeleton functions like a monorail system within the cell, enabling the movement of materials via motor proteins.

The invention of the microscope was crucial for scientists to observe and understand cellular structures.

Optical microscopes use light and lenses for magnification, while electron microscopes utilize magnets and electrons.

Electron microscopes can provide higher magnification and resolution, but may require sample destruction.

Fluorescent dyes in optical microscopes allow for live cell imaging and the observation of cellular processes.

There are two major types of cells: prokaryotic, lacking a nucleus, and eukaryotic, which contain a nucleus.

Prokaryotic cells include bacteria and archaea, while eukaryotic cells encompass multicellular organisms.

All cells share common features such as DNA, a cell membrane, cytosol, and ribosomes.

Eukaryotic cells have specialized organelles like mitochondria, which are crucial for energy production.

The nucleus houses the cell's genetic material and controls gene expression and protein synthesis.

Ribosomes are the cellular machinery responsible for protein synthesis, with distinct structures in prokaryotic and eukaryotic cells.

Vesicles are membrane-bound containers that transport materials within the cell and are involved in various cellular processes.

The rough endoplasmic reticulum is a cellular factory for protein synthesis and membrane production.

The Golgi apparatus modifies and packages proteins for transport within the cell, functioning like a shipping department.

The cytoskeleton provides structural support and enables cell movement, similar to a bridge's framework.

The smooth endoplasmic reticulum is involved in lipid synthesis and detoxification processes.

Mitochondria generate ATP through a process that resembles bacterial metabolism, supporting the endosymbiotic theory.

Vacuoles in plant cells maintain turgor pressure and store water, while in animal cells, they are involved in waste processing.

The cytosol contains dissolved substances and is more complex than previously thought, with concentration gradients.

Lysosomes contain digestive enzymes for breaking down cellular waste and play a role in programmed cell death.

Centrioles are involved in cell division and positioning, forming the spindle fibers during mitosis.

Transcripts

Hi. It's Mr. Andersen and in this podcast I am going to take you on a tour

of the cell. We're going to talk about the different types of cells and then how the

structures inside a cell fit their function.

The first thing though that we need to talk

about is why cells are small. The reason cells are small is that material moves into a cell

through a process called diffusion. So oxygen get's in that way and carbon dioxide is going

to move out in the same way. And so it would take a long time for material to diffuse into

a cell. And so what we can do, is we can actually make that volume the same but we can increase

the surface area. And now the distance that material has to move is actually relatively

small. And you also might also think to yourself, why are the infinitely small? Why are they

really really tiny? Well the reason why is that the material inside a cell, the information

inside the cell, like the DNA and the machinery of the cell, has to be able to fit inside

the cell. And so there's like a perfect sweet spot in size for all the different types of

cells that we have.

Another thing I want to talk about is cells are not boring. When I grew up I had this

idea that a cell was like a bag of jelly and you had stuff like a nucleus inside it and

it would essentially float around. This is probably perpetuated by biology teachers always

in assigning like an edible cell assignment. And if you actually look inside a cell, it's

incredibly complex. They have this cytoskeleton that's made up of a number of different macromolecules.

It's like a lattice inside the cell. And all the organelles fit within that lattice and

it works almost like the monorail. As materials moved around on this monorail using these

motor proteins. And I'm not joking, they literally walk like that on the monorail. And so they're

incredibly complex, cells are. But they're often times misunderstood and they were totally

invisible to scientists until we invented the microscope. In other words, we couldn't

see them. If you look at your hand, you can't see the cells.

And scientists couldn't see them either so

they didn't know what was going on until they discovered and invented the microscope. It

comes in two different types. You basically have optical microscopes and then electron

microscopes. Optical microscopes use light and lenses to magnify the image. If you've

ever used binoculars and then you turn it upside down and hold it close to your hand

you actually have a real simple microscope. And so that's the way that they work.

If it's an electron microscope, what they're

using is a number of magnets. And those magnets will be used to focus electrons either through

an image or bouncing it off an image. So we've got transmission and scanning electron microscopes.

How does this work? Well a quick demo would be to take a big magnet and hold it really

close to an old television or your computer screen. Don't Do This! If you were to do it,

it would permanently ruin your monitor or your computer screen, but basically what it's

doing is the magnet is changing the path of the electrons and by doing that we can

actually increase the magnification of the specimen.

So here's some pictures that were taken with

these. This would be paramecium with an optical microscope, one that you have in a typical

biology classroom. These ones are taken by a transmission electron microscope. These

are little viruses. Or this would be an ant that you're looking at. Now these two are

dead. Because the material, in order to look at it, the process is actually going to destroy it.

In fact in here you have to put a thin layer of metal on it that we can bounce it

off on a scanning electron microscope.

And so the future is electron microscopes but it's also what are called fluorescent

optical microscopes. So we're coming up with these beautiful fluorescent dyes, and you

saw one on the first page in this podcast. And that we can stain material that can stay

alive. I even saw one stain this last summer that was a live-dead stain. And so you would

stain it and it would show you all the cells that were alive at that point and dead at

that point. It's really cool. We're getting some great visualization of the cell.

First thing you should know is there are two

major types of cells. We have what are called prokaryotic cells and then eukaryotic cells.

Prokaryotic cells are going to lack a nucleus. They're before the egg if we break down that word.

So there's going to be no nucleus. Eukaryotic cells are going to have nucleus.

What types of things are prokaryotic? Really

only two things, bacteria are going to be prokaryotic and the the archaea bacteria,

let me try to spell that correctly, are going to be prokaryotic. Eukaryotic are going to

be things you think of as alive that aren't microscopic. Things like plants, animals,

fungus, protists, things like that that are really really large. The scale is bad here

because if I were to scale it right, the bacteria would be about the size of this mitochondria.

So these are really, really small. But there's some similarities between the two. In other

words, all cells are going to have nucleic material. So they're going to have DNA.

All cells are going to have a cell membrane around the outside, some form of cytosol on the inside

and they're also going to have ribosomes. They may differ but all cells are going to

have those things.

As we move to eukaryotic cells, let me go back again, then we're going to have organelles,

so we're going to have organs within the cell that you're familiar with. Like a mitochondria

would be an example of that. And so basically prokaryotic cells are simpler, I'll talk more

about them when I talk about bacteria, but most of the time in this podcast I'm going

to talk about eukaryotic cells. This would be an animal cell, I could tell right away.

And so let's kinda look through an animal

cell. So basically these are the major organelles that are found within a cell, from the nucleus

all the way down to the centriole. And so what I'm going to do is go through it, show

you where they are, talk about what they do and then you probably want to review at the

end, go through all of them and see how much of the information that you have actually

picked up.

So let's start with number 1and that's the nucleolus. Nucleolus is going to be found

within the nucleus. And I used to be confused on how this actually works. What they do is

all the chromosomes that are within the nucleus, what they do is they put all of their genes

to make ribosomes in one area within the nucleus. And that as a result, since we have a lot

of proteins inside here, is going to be a little darker when it gets stained. And so

this is an area where the chromosomes are all producing ribosomal RNA to make the ribosomes.

It's going to be right there. It's kind of a two step process. So basically what happens

is in this area they're going to produce ribosomal RNA, it'll roll out here, it'll actually build

some of the proteins using ribosomes outside of the cytoplasm and then those proteins will

move back where we assemble the building blocks of proteins which are going to be ribosomes.

And so I talked about a lot of different things. But what did I mean to talk about, well the

nucleolus is an area where the ribosomes are assembled inside the nucleus.

If we go to the next one, the next one is

going to be the nucleus and that's one of the first organelles that was ever discovered.

This is a beautiful fluorescent dye on the nuclei. So what's the function of the nucleus?

Well, when I grew up I always heard it's like the brain of the cell. That's really oversimplifying

it. What's inside here? Basically we've got DNA, so the genetic material of the cell is

going to be found inside the nucleus and that's going to determine you know, what kind of

cell it's going to become. But it is also going to control the cell. In other words

we're going to make proteins. We're going to make enzymes at a certain time and as a

result of that a cells going to do something. And so if you still want to think that it's

the control center of the cell, that's okay. But a better way to think about it is just

where the genetic material is. And it's also going to have little pores on the outside

that will become important when we starting talking about transcription and translation.

So they're going to be little holes on it. And that's how material can move out and material

can move in through those little holes.

Okay. Next we get to the ribosome. Ribosome generally growing up I represented those as

little dots inside the cell. It's a little more complex than that. The two parts of it,

you're going to have a small subunit on the bottom. You're going to have a large subunit

on the top. And the messenger RNA is going to move through that and then on the top we're

going to bring in the transfer RNA and we're actually going to build our protein off of

it. And so the function of the ribosome is going to be to build proteins. And prokaryotic

and eukaryotic have different ribosomes and that's how some of our antibiotics actually work.

A vesicle is a broad term. A vesicle basically means a membrane bound container. And they're

really really small and sometimes they're really really big. So a vacuole would be an

example of a vesicle. And they move material around, depending on what they do. Like a

transport vesicle would move material around.

Next we get to the level of the rough ER or the rough endoplasmic reticulum. It's actually

a membrane that is continuous with the nucleus. And so we've got this folded membrane and

it comes out from the nucleus. You then have ribosomes that are sitting on the outside

of it. That's why it's called rough ER. I like to think of this as the factory inside

of a cell. And so basically what you're going to have is this membrane. So we've got a membrane

like this and then you're just going to have a ribosome that sits on the top of it. So

basically what you can do is as the messenger RNA comes through we can make the proteins

that we want to make. And so it's like a factory. It's going to be where we make the material.

It also will produce the membranes that are going to be used within the cell.

Next we get to the level of the Golgi Body.

I like to think it looks kind of like a pita bread that is folded on top of itself. So if

we were to say where are these proteins going? They're going to be created in the endoplasmic

reticulum. They'll then be packaged in a little transport vesicle and moved to the Golgi apparatus.

At the Golgi apparatus we're going to modify that. We're going to add things like carbohydrates

to those proteins. We're going to snaz them up a little bit and then we are going to send

them on their way. So another way to think about that is that it's like a UPS. In other

words it is a shipping part of the cell. Things come in as a transport vesicle. They're going

to go out as a transport vesicle and they're going to to where they need to go within the

cell.

Next we've got the cytoskeleton. Cytoskeleton is the structure inside the cell. It actually

gives it that physical structure. If a cell were to move around that's going to have to

be like an amoeba that's going to do with a cytoskeleton as well. The way I like to

think about this is through analogy. So it's kind of like a bridge. So on a bridge you're

going to have two things. Those are going to be supporting the bridge. But then you're

going to have these really thin wires that attach it up, like on the Golden Gate Bridge.

And so basically inside a cell we have those two things. We have the big things. Those

are called microtubules and they're made from a protein called tubulin. And then we have

these really thin things and those are called microfilaments. And what the big things, the

microtubules do is they provide compressional support, just like the weight of the bridge

is supported by them. And then those thin microfilaments are going to provide tensional

support. And so if you think of a cell like the Golden Gate Bridge but kind of inverted

inside it, that's a good way to think about what a cytoskeleton is.

Next we get to the smooth ER. What's it missing?

Ribosomes. What's it producing? It's going to produce a lot of the lipids, cholesterol,

things like that in the cell. It's also really really important in detoxification, so breaking

down toxins. And so if you're an alcoholic, hopefully not, but if you're an alcoholic

basically the more you drink the more your body is going to build up smooth ER inside

it's cell. So you're going to have to drink more and more and more and more.

Next we've go the mitochondria. Mitochondria

you know is the area where we're going to generate energy. What's it really generating?

That's going to be ATP, in the form of ATP. It basically has a folded membrane inside

a membrane. It looks a lot like a bacteria and that's because scientists think they became

parts of our cells through endosymbiotic theory. In other words, they became parts of the cell,

they produce ATP for that cell and then they get a place to live. What's some evidence

for that? Well, they have their own DNA they produce on their own through binary fission.

And so it's pretty much accepted as a biological fact.

Now we have the vacuole. Vacuole is going

to be something that we find inside plants not in animals, generally large vacuoles.

And in this plant cell here what it's doing is it's storing water, so it stores that balance

and pressure, that turgor pressure that keeps the cell properly inflated. Some protists

will actually have a contractile vacuole that can pump water out when they're living in

a fresh water environment as well. We've got vacuoles but they're really small in general

in animals and they're used for like endo and exocytosis.

Next we've got the cytosol. Cytosol, you can

think of as like the dissolved material so its the fluid but it actually contains solutes

inside it. We used to think that was about it, but what we are finding is there are concentration

gradients within the cell. And so even the cytosol itself is pretty complex.

Next we go to the level of the lysosome. The

lysosome is going to be, sometimes it's be coined as like the suicide sac. What does

it really have inside it? It has these digestive enzymes inside it and it's contained within

this membrane. And so basically what we can do is we could have that go next to another

vesicle that has material that we want to break down and those digestive enzymes will

go in there and it'll break it down. Or where it gets its name from is if we were to pop

this lysosome basically what happens is those digestive enzymes would go throughout the

cell and would kill the cell, dissolve the cell. And so the process of apoptosis, where

the cell kills itself, is a product of lysosomes.

And finally we have the centriole. Centriole is part of what's called the centrosome. And

basically its important in positioning within the cell. So dependent upon where the centriole

is, its also going to set up where the nucleus is going to be and where the other parts of

the cell are going to be. It's also important as a cell divides. It's going to be, as it

migrates to either side it's going to initiate the formation of the spindle. And the spindle

is going to be attached to the chromosomes and going to pull it to either side. And so

we have those but if you were looking to higher plants, they don't have centrioles and their

role is somewhat undefined.

And I think we could say the same thing for all of these. That we really have an idea

of what they do, but they probably do lots of other things that we're really not familiar with.

And so this is where the podcast becomes scary. I'm going to make all those terms disappear

and basically if you hit pause, could you go though at the beginning and list what is

number 1? What is number 2? What is number 3? What is number 4? What does number 1 do?

And if you can't do that, you really don't understand it. And working with kids in class,

what I found that when you're trying to learn the parts of the cell, sometimes it's easier

to just build some flash cards and go through the flash cards because if you can't get it

right now, then you don't got it.

And so that's the tour of the cell and I hope it was fun and I hope that was helpful.