A review of structures found inside the plasma membrane of the eukaryotic cell. This includes the nucleus, cytoplasm, cytoskeleton, centrosomes, ribosomes, endoplasmic reticulum, golgi apparatus, vacuoles, lysosomes, peroxisomes, mitochondria, and chloroplasts.
Microbiology, part 13: Eukaryotes - Structures Inside the Plasma Membrane
Full Transcript: Microbiology, part 13: Eukaryotes - Structures Inside the Plasma Membrane
Full Transcript: Microbiology, part 13: Eukaryotes - Structures Inside the Plasma Membrane
Hi, I'm Cathy with Level Up RN. In this video, I will be discussing eukaryotic cells, with a focus on the structures found within the plasma membrane. In my next video, I will talk about the plasma membrane and structures found outside the plasma membrane. At the end of the video, I'm going to give you guys a quiz to test your understanding of some of the key facts I'll be covering, so definitely stay tuned for that. And if you have our Level Up RN Microbiology Flashcards, go ahead and pull out your flashcards so you can follow along with me, and pay close attention to the bold, red text on the back of the cards because those are the things that you are likely to see show up on a micro exam.
First up, we have the nucleus of the eukaryotic cell. This is the organelle that contains the cell's DNA, which is organized into multiple linear chromosomes. Let's talk about how DNA is packaged in the nucleus. So DNA molecules first wrap around histone proteins, forming a bead-like structure on a string called a nucleosome. Nucleosomes coil and condense to form chromatin, which is a fibrous complex consisting of repeating units of nucleosomes. During cell division, chromatin further condenses to form chromosomes, but in between cell division, chromatin remains in its less condensed state. In addition to DNA, the cell's nucleus also contains the nucleolus, which is where ribosomal RNA is synthesized, and ribosomal subunits are assembled. And then surrounding the nucleus, we have the nuclear envelope. This is a double membrane that consists of two separate lipid bilayers. And then within the nuclear envelope, we have nuclear pores, which are channels that control the movement of materials in and out of the nucleus.
Let's now work our way outside the nucleus, where we will find the cytoplasm. The cytoplasm is basically everything between the nuclear envelope and the plasma membrane. This includes a gel-like substance called cytosol, as well as the structures suspended in the cytosol. Within the cytoplasm of a eukaryotic cell, you will find the cytoskeleton, which is a matrix of protein fibers and tubes that provide structural support for the cell, and also allows for the transportation of substances throughout the cell. The cytoskeleton is made up of microfilaments, intermediate filaments, and microtubules. So the microfilaments are long rod-like structures composed of actin. The intermediate filaments are fibers composed of polypeptides. And then the microtubules are hollow tubes composed of the protein tubulin. Within animal cells, you will also find centrosomes, which are basically microtubule organizing centers that are important in cell division. So centrosomes form the mitotic spindle, which separates chromosomes during mitosis and meiosis. Each centrosome consists of 2 centrioles, and each centriole consists of 9 triplets of microtubules held together by proteins.
Next, we're going to talk about ribosomes, which are the structures in the cell responsible for protein synthesis. In a eukaryotic cell, ribosomes may be freely floating in the cytosol or be bound to the rough endoplasmic reticulum. Unlike prokaryotic ribosomes, which are 70S ribosomes, eukaryotic ribosomes are 80S ribosomes. Each 80S ribosome consists of a small 40S subunit and a large 60S subunit.
Now let's talk about the endoplasmic reticulum, or ER. The ER consists of interconnected tubules and flattened sacs called cisternae. The rough ER is studded with ribosomes on the outer surface and is involved in protein synthesis. The smooth ER does not contain any ribosomes, and is involved in lipid synthesis, the detoxification of substances, and carbohydrate metabolism.
Next, let's talk about the Golgi apparatus, which serves as the distribution center for the cell. The Golgi apparatus receives lipids and proteins from the endoplasmic reticulum, and often adds carbohydrates to them, forming glycoproteins and glycolipids. Once these lipids or proteins have been modified, then transport vesicles pinch off from the Golgi apparatus and travel to their final destination. Some will be secreted out of the cell, some will be incorporated into the plasma membrane, and in some cases, those vesicles will become lysosomes. Like prokaryotes, eukaryotes contain vacuoles, which are organelles that serve a variety of functions in the cell. Some store toxins and waste products, gas vacuoles store gas, which allows the cell to adjust its buoyancy, and some vacuoles get rid of excess water in the cell. So those are just a few examples of how a vacuole may function within a cell.
A lysosome is another organelle found in both prokaryotic cells and eukaryotic cells. This organelle contains digestive enzymes that break down particles in the cell, such as cellular debris and microorganisms, and by digesting these particles in the lysosome, this protects the rest of the cell from being damaged by those digestive enzymes. Peroxisomes are organelles that are only found in eukaryotic cells. They produce hydrogen peroxide and carry out oxidative reactions. They are also involved in lipid biosynthesis.
Now let's talk about mitochondria, which are large, complex organelles in eukaryotic cells, where many of the steps involved in aerobic cellular respiration occur. And just so you know, we have a separate video that goes into all the important details about cellular respiration. Mitochondria have an outer membrane, and an inner membrane folded into cristae. Oxidative phosphorylation, which is a key part of cellular respiration, occurs along this inner membrane. Inside the inner membrane, we have the mitochondrial matrix, and the citric acid cycle, which is also involved in cellular respiration, occurs in this matrix. The matrix also contains DNA, ribosomes, and metabolic enzymes.
Now let's talk about chloroplasts, which are organelles found in plant and algae cells where photosynthesis occurs. Each chloroplast has an outer membrane, an inner membrane, and a thylakoid membrane system. Inside the inner membrane, we have stroma, which is a gel-like matrix, and contained within that stroma, we have DNA, ribosomes, and metabolic enzymes. Photosynthesis occurs along the thylakoid membrane and in the stroma. And of note, we have a separate video that goes into the important details about photosynthesis.
The last thing I wanted to mention before we do our quiz is that mitochondria and chloroplasts have 70S ribosomes, which is the same as prokaryotic cells, which is a key piece of evidence that supports the endosymbiotic theory, and I have a separate video that goes into details about this theory. So to reiterate, eukaryotic cells have 80S ribosomes, but the mitochondria and chloroplasts that are inside the eukaryotic cells have 70S ribosomes.
All right, it's quiz time, and I have five questions for you. Question number one. Which organelle serves as the distribution center for the eukaryotic cell? The answer is the Golgi apparatus. Number two. Which structures are responsible for protein synthesis in the cell? The answer is ribosomes. Number three. Which organelle contains digestive enzymes and breaks down particles in the cell? The answer is a lysosome. Number four. What are the three main components of the cytoskeleton? The answer is microfilaments, intermediate filaments, and microtubules. Number five. Which organelle is the site of photosynthesis in a eukaryotic cell? The answer is the chloroplast. All right. That's it for this video. I hope you did great with that quiz, and I hope you found this video to be helpful. Take care and thank you so much for watching.
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