Transcript

Introduction

Hello!

My name is Ethan from the UNT Learning Center.

In this video, we’ll be going over the origin of cells and organelles as well as the different types
and functions of organelles in eukaryotic cells.

Just as a preview, here are fully labeled plant and animal cells with all the organelles we’ll cover
in this video, plus some extra ones. This diagram will be referenced at the end of the video to go
along with some labeling practice.

Image 1
Origin of Cells

So, where do cells come from? On the right you can see a diagram of a fully functioning
eukaryotic cell. But its predecessor is shown on the left. Cells stem from primitive structures
called micelles and liposomes. On the left, you can see that a micelle is just a bunch of
phospholipids self-arranging in water. A liposome, on the other hand, occurs where you have
two layers of phospholipids, almost like one micelle wrapping around another micelle.

Image 2 Image 3

Both of these structures form spontaneously in water due to the chemical properties of
phospholipids.

These phospholipids have a polar head and nonpolar tails. If you can recall some chemistry,
polar parts of molecules can also be called hydrophilic, which means “water-loving”, while
nonpolar parts of molecules can be called hydrophobic, which means “water-fearing”. This
means that polar regions will try to stay in contact with water (because water is polar) and
nonpolar regions will try to avoid water.

Therefore, if you imagine water surrounding a collection of phospholipids, they arrange in a

spherical micelle shape to maximize the contact between their polar heads and water while
minimizing the contact between their nonpolar tails and water.
 Image 4

Once you have a micelle, you have the potential for another micelle to form inside of the first
one creating a bilayer of phospholipids. This is what we call the plasma membrane today.
Beyond this, we don’t know every other step that led to DNA inside the membrane, enzymes that
read the DNA, and proteins that are produced.

But the important thing is to know how a membrane forms, which defines each and every cell as
its own functioning unit. Also, it’s important to understand that the polar head and nonpolar tails
of phospholipids cause a membrane to form spontaneously in water.

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So, cells are the building blocks of life. Everything that we consider living has microscopic cells
that can function on their own. Some organisms like bacteria consist of a single cell and are
called prokaryotes, while organisms like us are multicellular and are considered eukaryotes.

The main differences you want to know between prokaryotes and eukaryotes is as follows:

Prokaryotes are usually unicellular, have NO nucleus, and NO membrane bound organelles.

However, eukaryotes are usually multicellular, they DO have a nucleus, and they DO have
membrane bound organelles. As with anything, there are some exceptions. For example, there
are some unicellular eukaryotes like algae or protozoa.

Image 6

Here are diagrams showing a prokaryotic cell on the left and a eukaryotic cell on the right.
Notice that the prokaryotic cell has no membrane-bound organelles, while the eukaryote has a
bunch of organelles scattered throughout.
Image 7 Image 8

Now that we know the difference between prokaryotes and eukaryotes, we can start going
through the organelles found in eukaryotic cells. Here’s a list of all the major organelles we’ll
learn about:

Plasma membrane, cell wall, cytoplasm, nucleus, ribosomes, endoplasmic reticulum, golgi
apparatus, mitochondria, chloroplast, vacuoles, lysosomes

Organelles

Let’s go through each of the organelles individually.

The first one is the plasma membrane. As we talked about earlier, it is composed of a bilayer of
phospholipids. It contains many proteins such as ion-transport channels, glycoproteins, and
carrier proteins used for ion transport, cell recognition, and general transport, respectively.

Additionally, we describe the membrane as a “Fluid Mosaic Model” because all the components
of the membrane can shift around throughout the membrane.

Image 9
The cell wall is similar to the plasma membrane; however, it is more rigid and only found in
plant cells and prokaryotes. Animal cells do not have cell walls. It provides structure, support,
and protection. There are three main regions of the cell wall: the primary cell wall, which is the
outermost layer, the secondary cell wall, which is the layer closest to the plasma membrane, and
the middle lamella, which is the region in between individual plant cells.

Image 10

Here’s a diagram clearly showing the different layers of a plant cell wall.

Image 11
The cytoplasm is all the interior part of a cell, and it’s a gel-like fluid that helps hold organelles
in place. This is where all the chemical reactions within a cell occur if they aren’t occurring
inside another organelle.

Image 12

The nucleus is where genetic information is stored, which is DNA for eukaryotes. It contains the
instruction manual for each and every cell. The nuclear envelope is a double membrane that
defines the nucleus, and it contains nuclear pores to exchange molecules with the rest of the cell.

Deeper in the nucleus is a region called the nucleolus, which helps produce ribosomes. Also, the
nucleus is the location where transcription occurs to turn DNA into mRNA before proteins are
made.

Image 13
Ribosomes are technically not membrane-bound organelles, but they are a vital part of the cell.
They are a bundle of RNA and proteins that synthesize proteins from mRNA. They are located
all throughout the cell in the cytoplasm and on the endoplasmic reticulum.

Image 14

The endoplasmic reticulum functions to take mRNA produced in the nucleus and turn it into
proteins by using ribosomes. We call the part of the endoplasmic reticulum that has ribosomes
“rough” and the part without “smooth.”

The smooth endoplasmic reticulum has three main functions: lipid synthesis, detoxification, and
calcium storage.

The golgi apparatus tags and transports proteins to the correct location in the cell. It receives
proteins from the rough endoplasmic reticulum and puts chemical tags on those proteins. This is
to ensure that they end up in the right location. It’s analogous to the “post office” for a cell.

It has a cis face that faces the endoplasmic reticulum and nucleus, and it has a trans face that
faces the plasma membrane.
 Image 15

The mitochondria produces energy for the cell in the form of ATP, which stands for adenosine
triphosphate. It does this through a process called cellular respiration. A couple interesting facts
are that the mitochondria has its own DNA and a double membrane.

The inside of the first membrane is known as the intermembrane space, and the inside of the
second membrane is known as the matrix.

Image 16

The chloroplast has the job of performing photosynthesis, which turns sunlight into usable food
called glucose, in plant cells. Chloroplasts contain three main features: thylakoid stacks, which
are membranous sacs where photosynthesis actually occurs, the stroma, which is like the
cytoplasm but for chloroplast, and a double membrane.
Similarly to mitochondria, chloroplasts have their own DNA.

Image 17

Vacuoles have the purpose of storing various molecules the cell needs. They are very important
in plant cells as they help to maintain what’s called “turgor pressure”, which gives structure to
that plant. Whenever you see a plant wilting, it’s due to a lack of water in their central vacuole,
which leads to a lack of pressure and a lack of structural support.

Image 18
The final organelle we will cover is the lysosome. Lysosomes are just a specialized vesicle that
contains digestive enzymes to break down molecules inside the cell. Like other vesicles, the
lysosome is a simple membrane made of phospholipids.

Image 19

Conclusion

So, back to our original diagrams. Take some time to pause the video and try to fill in the blanks
of the different organelles. The ones blocked in dark blue are used twice, and the ones blocked in
green are only found in plant cells.

Image 1
How did you do? Here is the key for the diagram. Feel free to pause the video to check your
work.

Image 1

If you would like additional practice on specifically the functions of organelles, I recommend
that you go through the practice quiz I’ve made in Kahoot. The link to the quiz is in the
description below the video (also posted below).

https://create.kahoot.it/share/biol-1710-organelles-1/27ca7d44-93ef-4121-8e69-7498e1a891ae

I hope you now have a better understanding of cells and organelles. If you have any questions,
you can visit learningcenter.unt.edu for various resources and services.
 References

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https://science.howstuffworks.com/life/cellular-microscopic/plant-cells-animal-cells.htm

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ThoughtCo. Retrieved April 6, 2020, from https://www.thoughtco.com/all-about-animal-cells-
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6. Original Diagram by Ethan Neumann

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