Microbiology, part 10: Prokaryotes - Structures Inside the Plasma Membrane

Hi. I'm Cathy with Level Up RN. In this video, I will be discussing prokaryotic cells. Specifically, I'll be talking about structures found inside the plasma membrane. I will also be talking about endospores and the process of sporulation. And then in my next video, we will talk about the plasma membrane and structures found outside the plasma membrane, including the cell wall. At the end of the video, I'm going to give you guys a quiz to test your understanding of some of the key points 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 get tested on in your micro class.

Using the illustration that you will find in our microbiology flashcard deck, let's talk about some of the key structures that you need to be familiar with inside the plasma membrane of the prokaryotic cell. So first of all, we have the cytoplasm, which is everything contained within the plasma membrane. This includes a gel-like substance, which is cytosol, and all the structures suspended in the cytosol. The nucleoid is the region within the prokaryotic cell that contains the cell's genetic material. As a reminder, prokaryotic cells contain a singular circular chromosome that is not bound by a nuclear membrane. In addition to this chromosome, many prokaryotic cells also have plasmids. Plasmids are circular DNA molecules found outside the chromosome that often provide an advantage to the cell, such as antibiotic resistance. You can think of plasmids as bonus genes. Next, you will see ribosomes, which are structures within the cell that are responsible for protein synthesis. They are composed of protein and specialized ribosomal RNAs.

Prokaryotic ribosomes are 70S ribosomes, and each ribosome is composed of a small 30S subunit and a large 50S subunit. It's important to note that this is different from eukaryotic cells, which contain 80S ribosomes. Within prokaryotic cells, you can also find inclusions, which are structures that store excess nutrients. Examples of inclusions include carboxysomes, which store enzymes that allow bacteria to fix carbon dioxide, or gas vacuoles, which store gas, which allows the cell to adjust its buoyancy. So more gas in the inclusion will make the cell more buoyant. Another structure that may be seen within the prokaryotic cell is an endospore. An endospore is a dormant structure that protects the bacterial genome if the environmental conditions become unfavorable.

So the normal active form of a cell is referred to as a vegetative cell. This is a cell that is metabolically active and reproduces. So when environmental conditions are favorable, we will see vegetative cells. However, if the environmental conditions become unfavorable, for example, if there is a lack of nutrients or the cell is being exposed to extreme temperatures or chemicals, then the cell will undergo sporulation. This is the process in which a vegetative cell produces an endospore. If and when environmental conditions improve, the endospore will undergo germination, which is the process in which an endospore returns to its vegetative state.

So understanding the steps that occur during sporulation is definitely important to know for your micro class. So let's take a look at that now. During sporulation, the cell first replicates its DNA, and a septum is created that separates the two copies of the DNA into a mother cell and forespore. Next, a plasma membrane forms around the forespore's DNA. The mother spore engulfs the forespore, which surrounds the forespore with a second membrane. Next, a cortex made of peptidoglycan forms between the two membranes, and then a protein spore coat forms around the cortex. And then lastly, the mother cell lyses, or breaks open, and the spore is released.

All right. It's quiz time, and I have five questions for you. Question number one, what do you call the gel-like substance found in the cytoplasm of the prokaryotic cell? The answer is cytosol. Number two, blank are circular DNA molecules found outside the chromosome in a prokaryotic cell. The answer is plasmids. Number three, blank are structures responsible for protein synthesis in the prokaryotic cell. The answer is ribosomes. Number four, blank is a dormant structure that protects the bacterial genome when environmental conditions become unfavorable. The answer is an endospore. And number five, what do you call the process in which the endospore returns to a vegetative state? The answer is germination.

All right. Hope you did great with that quiz, and I hope this video was helpful. Take care, and good luck with studying.

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