Introduction to Eukaryotic Organelles - Online Tutor, Practice Problems & Exam Prep

Eukaryotic cells contain various membrane-bound organelles, with differences between animal and plant cells. Key organelles include lysosomes, unique to animal cells, and chloroplasts and cell walls, exclusive to plant cells. Ribosomes, essential for protein synthesis, exist as free or attached to the rough endoplasmic reticulum, with eukaryotic ribosomes being larger (80S) than prokaryotic ones (70S). Understanding these organelles is crucial for grasping cellular functions and processes, including the endomembrane system, energy-related organelles, and the cytoskeleton.

Introduction to Eukaryotic Organelles

In this video, we're going to begin our introduction to Eukaryotic Organelles or organs inside of the cells. Recall from our previous lesson videos that eukaryotic cells contain several membrane-bound organelles. Moving forward in our course, we're going to discuss many of these membrane-bound organelles. It's important to note that both animal and plant cells are eukaryotic, and so they both contain eukaryotic organelles. However, some of the organelles of animal and plant cells actually differ from each other, and that's important to keep in mind.

Below in our example of eukaryotic organelles, notice that we're showing you our representation of an animal cell on the left-hand side and our representation of a plant cell on the right-hand side. You'll notice that the organelles in the middle are shared between both animal and plant cells, whereas the organelles on the far left are only found or associated with animal cells, and the organelles on the far right are only found and associated with plant cells. It's also important to remember that these are just general representations of animal cells and plant cells, but not all animal cells and plant cells will have all of these organelles. They're just generalized representations.

When talking about the animal cell, we will focus on how lysosomes are one of the characteristic organelles that are only found in animal cells but not found in plant cells. When discussing plant cells, we'll talk about how chloroplasts and cell walls are characteristic of only plant cells, but not so much in animal cells. In the middle, we have organelles that are common to both animal and plant cells.

Moving forward in our course, we'll talk a lot more about each of these organelles. For example, the mitochondria, which are not just in eukaryotic cells, but also in prokaryotic cells, which we're also not talking about here. They both have a rough ER (rough endoplasmic reticulum) and a smooth endoplasmic reticulum, which we're showing you here. They both also have structures called ribosomes, which are these tiny little blue dots that we're showing you. They both have a Golgi apparatus, and they both are going to have peroxisomes like what we see here. Once again, we'll be talking about each of these organelles in their own separate videos moving forward.

This concludes our brief introduction to eukaryotic organelles. Moving forward in our course, we're going to talk a lot more about each of these organelles. I'll see you all in our next video.

Eukaryotic Ribosomes

In this video, we're going to talk about eukaryotic ribosomes. And so sometimes ribosomes are considered organelles. However, they are referred to as nonmembranous organelles because they are not made up of membranes. And so ribosomes can either be free ribosomes or, in other words, floating around in the cytoplasm, or the ribosomes can be attached ribosomes where they will be attached to another organelle, for example, the rough endoplasmic reticulum or the rough ER for short.

Now eukaryotic ribosomes are different than prokaryotic ribosomes. Instead of having a 70S ribosome like what prokaryotes have, eukaryotes have an s80 ribosome that is larger, and it has larger ribosomal subunits as well. It has a large s60 ribosomal subunit instead of having a large s50 ribosomal subunit like what prokaryotes have. And it has a small s40 ribosomal subunit, which is larger than the small ribosomal subunit of prokaryotes, which is s30 ribosomal subunit. Now each of these ribosomal subunits is actually going to contain ribosomal RNA. The large ribosomal subunit in eukaryotic ribosomes has 3 ribosomal RNAs which are the s28, the s5.8, and the s5 ribosomal RNAs. And the small ribosomal subunit in eukaryotes is an s18 ribosomal RNA.

And once again, recall that the 's' is the unit for Svedberg units, which is representing the sedimentation coefficient and is really just describing the size, in its most simplistic state. You could just think of it as the size of the subunit. And so, over here, what we have is an image representing the eukaryotic ribosome structure. And so once again, eukaryotes have an s80 ribosome, and so this entire circular blue structure that you see right here is representing the entire structure of the eukaryotic ribosome. And so, notice that the eukaryotic ribosome has 2 subunits, ribosomal subunits. It has this large ribosomal subunit, and it has the small ribosomal subunit down below. The large ribosomal subunit in eukaryotes is a s60 large ribosomal subunit. And the small ribosomal subunit in eukaryotes is a s40 small ribosomal subunit. Now, once again, the large ribosomal subunit and the small ribosomal subunit both contain ribosomal RNAs, which are represented by these little yellow strands that you see throughout.

And so the large ribosomal subunit has 3 ribosomal RNAs, which again are the s28, the s5.8, and the s5 ribosomal RNAs, and those are grouped based on their size. And so the largest one here would be the s28 ribosomal RNA, the next largest would be the s5.8 ribosomal RNA, and then the smallest ribosomal RNA over here would be the s5 ribosomal RNA. And in the small ribosomal subunit there is one ribosomal RNA which is the s18 ribosomal RNA as we indicated up above. And so when the large ribosomal subunit, the s60 large ribosomal subunit, and the s40 small ribosomal subunit come together and complex together, that's when they form the s80 ribosome which is a completely intact ribosome, eukaryotic ribosome. Now notice that in the red box, in this area right here, we have these three regions which are representing the active site of the ribosome where they will create proteins. And we'll get to talk more about this particular active site and those three compartments when we talk about protein synthesis and translation later in our course in a different video.

But for now, this is the eukaryotic ribosome structure. Now over here on the right, what we're showing you is our eukaryotic cell, and we're zooming into this particular region to show you how this blue structure that you see here is representing the rough endoplasmic reticulum or the rough ER, and there are ribosomes attached to the rough endoplasmic reticulum. And so all these blue little dots that you see on the rough endoplasmic reticulum over here, all of these little dots represent ribosomes that are attached to the rough endoplasmic reticulum. But notice that there are also some free ribosomes up above here that are free-floating in the cytoplasm. And this is the idea that we were mentioning right here on this line of text.

This here concludes our brief introduction to eukaryotic ribosomes, and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video.

What biomolecule does a ribosome synthesize in all types of cells?

• A. Lipids.
• B. Carbohydrates.
• C. Nucleic Acids.
• D. Proteins.
• E. Amino Acids.

Map of the Lesson on Eukaryotic Organelles

In this video, I'm going to introduce our map of the lesson on Eukaryotic Organelles, which is down below right here. And so this is actually a map of our lesson moving forward in our course. And so that means that you can use this image like a map, and you can actually use it to make predictions about what direction we're going to head into moving forward with our videos. And so let me explain to you how this map works. It works, starting at the top here. So we have eukaryotic cell organelles at the very top. And then moving forward through our lesson, we're going to be exploring the leftmost branches first, and then once we've explored the leftmost branches, we'll start to explore the right branches. So for example, we're going to start here at eukaryotic cell organelles, then we're going to explore the leftmost branches first. So we'll talk about the endomembrane system. Then we'll talk about the components that are part of protein secretion, which includes the nucleus, the endoplasmic reticulum, the rough ER and smooth ER, the Golgi apparatus, and the cell membrane. And then once we've explored the leftmost branches, what we're going to do is we're going to zoom out and start to explore the right branches, which includes cellular digestion, lysosomes, peroxisomes, and vacuoles. And then once we've explored all of these branches over here on the left, we're going to zoom back out and start to explore the new branch over here, energy-related organelles, and then talk about the mitochondria and the chloroplasts. And then once we've covered these, we're going to move on to the next branch and talk about the cytoskeleton, which includes microfilaments, intermediate filaments, and microtubules, and has a lot of resemblance to actual skeletons, which is why we've got this little skeleton here. And then once we've covered the cytoskeleton components, last but not least, we'll move on to the cell junctions at the end. Tight junctions, anchoring junctions, gap junctions, and plasmodesmata. And so this is basically, the way that we're going to cover videos moving forward in our course in that fashion, exploring the leftmost branches first. And so what this means is that you should be referring back to this map, as we move forward in our course, so that you can know exactly what direction we're headed in and how much is left within our lesson. And so keeping that in mind, of course, we're going to start off by exploring the leftmost branches first. So we're going to talk about the endomembrane system in our next lesson video. And so I'll see you all there.

Using the map above, which of the following is NOT a component of the cytoskeleton in eukaryotic cells?

• A. Intermediate filaments.
• B. Microtubules.
• C. Tight junctions.
• D. Microfilaments.

Using the map above, what two organelles produce cellular energy in eukaryotic cells?

• A. Mitochondria and Golgi Apparatus.
• B. Chloroplast and Nucleus.
• C. Lysosomes and Rough ER.
• D. Chloroplast and Smooth ER.
• E. Mitochondria and Chloroplasts.
• F. Microtubules and Chloroplasts.

Which of the following is NOT part of the Eukaryotic endomembrane system?

• A. Mitochondria
• B. Cell membrane
• C. Golgi Apparatus
• D. Lysosomes
• E. All are part of the endomembrane system

Here’s what students ask on this topic:

What are the main differences between eukaryotic and prokaryotic ribosomes?

Eukaryotic ribosomes are larger than prokaryotic ribosomes. Eukaryotic ribosomes are 80S, composed of a 60S large subunit and a 40S small subunit. In contrast, prokaryotic ribosomes are 70S, consisting of a 50S large subunit and a 30S small subunit. The 'S' stands for Svedberg units, indicating the sedimentation rate during centrifugation, which correlates with size and density. Additionally, eukaryotic ribosomes contain different ribosomal RNA (rRNA) components: the 60S subunit has 28S, 5.8S, and 5S rRNAs, while the 40S subunit has 18S rRNA. Prokaryotic ribosomes have 23S and 5S rRNAs in the 50S subunit and 16S rRNA in the 30S subunit. These differences are crucial for the function and structure of ribosomes in protein synthesis.

What organelles are unique to plant cells and not found in animal cells?

Plant cells have several unique organelles not found in animal cells. The most notable are chloroplasts and the cell wall. Chloroplasts are responsible for photosynthesis, converting light energy into chemical energy stored in glucose. They contain the pigment chlorophyll, which gives plants their green color. The cell wall, composed mainly of cellulose, provides structural support and protection. Additionally, plant cells often have large central vacuoles that store water, nutrients, and waste products, helping maintain cell turgor pressure. These organelles are essential for plant-specific functions such as photosynthesis, structural integrity, and storage.

What is the function of the rough endoplasmic reticulum in eukaryotic cells?

The rough endoplasmic reticulum (rough ER) is a crucial organelle in eukaryotic cells involved in protein synthesis and processing. It is termed 'rough' due to the presence of ribosomes on its surface, which are sites for protein synthesis. Newly synthesized proteins enter the rough ER lumen, where they undergo folding, modification, and quality control. These modifications can include glycosylation, where sugars are added to proteins. The rough ER also plays a role in the production of membrane-bound and secretory proteins, which are then transported to the Golgi apparatus for further processing and sorting. Thus, the rough ER is essential for producing and processing proteins destined for various cellular locations.

How do lysosomes function in animal cells?

Lysosomes are membrane-bound organelles in animal cells that function as the cell's digestive system. They contain hydrolytic enzymes capable of breaking down various biomolecules, including proteins, lipids, nucleic acids, and carbohydrates. Lysosomes are involved in several cellular processes, such as autophagy, where they digest and recycle damaged organelles and cellular debris. They also play a role in endocytosis, breaking down materials taken up by the cell from the extracellular environment. By maintaining an acidic environment optimal for enzyme activity, lysosomes ensure efficient degradation and recycling of cellular components, contributing to cellular homeostasis and health.

What is the role of the Golgi apparatus in eukaryotic cells?

The Golgi apparatus, also known as the Golgi complex, is a critical organelle in eukaryotic cells involved in modifying, sorting, and packaging proteins and lipids for secretion or delivery to other organelles. It consists of a series of flattened membrane-bound sacs called cisternae. Proteins and lipids synthesized in the endoplasmic reticulum are transported to the Golgi apparatus, where they undergo further modifications, such as glycosylation and phosphorylation. The Golgi apparatus then sorts and packages these molecules into vesicles, directing them to their appropriate destinations, including the cell membrane, lysosomes, or extracellular space. This organelle is essential for maintaining cellular organization and function.