The human body is incredibly complex. It consists of trillions of cells, and this is not surprising because everything in our body is made of cells. Our blood, our nerves, our muscles, and even our skin. A cell is the most basic unit of life, but it actually consists of a lot of different components called organelles. I like to think of organelles as tiny organs.
They perform specific functions for a cell, such as creating proteins from RNA, or transporting those proteins to different locations around the cell, or even using those proteins to convert the food you eat into energy that can be used by the cell. There are eight major organelles that you need to know about. The nucleus, ribosomes, the endoplasmic reticulum, the Golgi body, chloroplasts, mitochondria, vacuoles, and lysosomes. For each of these organelles, we are going to discuss their structure and their function.
So let's start with the nucleus. The nucleus is like the control center of the cell. It contains DNA, which basically determines everything about you, so it kind of controls you. The nucleus is surrounded by a membrane called the nuclear envelope.
This is a double membrane, meaning it has two layers. There's layer one and there's layer two. The nuclear envelope separates the contents of the nucleus from the cytoplasm. The envelope is covered in tiny pores that allow substances to exit and enter the nucleus.
But we can't just have anything entering and leaving the nucleus, so there are these protein structures called the pore complex that sort of guard the nuclear pore. They basically regulate what flows in and what goes out. But let's take a closer look inside the nucleus. Like I said before, your genetic material is stored in the nucleus of the cell.
That would be DNA and the proteins that modify it. Together, they're called chromatin. Chromatin is arranged in structures called chromosomes. Humans have 23 chromosomes in every cell. The funny thing is, you can't really distinguish chromosomes from each other in a non-dividing cell.
When a cell is in its regular state, as in not undergoing cell division, chromosomes are very loose, so all you can see is this mass of chromatin. But, when the cell is divided, dividing, the chromosomes contends, and you can actually differentiate one chromosome from another. The place where chromatin is most densely packed in the nucleus is called the nucleolus. Moving on to ribosomes.
Ribosomes are made up of proteins and something called rRNA, or ribosomal RNA. They are partly assembled in the nucleolus. What ribosomes do is they basically translate... the information in messenger RNA to produce proteins. And messenger RNA is basically just like a set of instructions on how to create a protein.
It's like a recipe. Ribosomes are present in two locations of the cell. They can either be freely suspended within the cytoplasm of the cell, or they can be attached to the endoplasmic reticulum. The ribosomes in the cytoplasm are called free ribosomes, and they generally make proteins that are used within the cytoplasm. The ribosomes attached to the ER, or endoplasmic reticulum, are called bound ribosomes, and they typically make proteins that are either incorporated into the cell's membranes or are exported from the cell to other locations in your body.
Speaking of the endoplasmic reticulum, that's the organelle we're going to be discussing next. There are two types of endoplasmic reticulum, rough ER and smooth ER. The rough endoplasmic reticulum is the one that has ribosomes bound to it, giving it a look of a rough texture. The rough ER is continuous with the nuclear membrane. So what happens in the rough ER is, as the ribosomes produce their proteins, the proteins are threaded into the pores of the rough ER.
And inside the rough ER, the protein folds into its unique shape. And while it's folding, it's transported through the pathway of the rough ER. Then, the protein leaves the rough ER through a vesicle to be transported to another location in the cell.
The smooth ER, on the other hand, is involved in lipid synthesis. Substances like steroids, phospholipids, and oils are produced here. The smoothie jar also stores calcium ions.
So what happens is calcium ions are pumped into the smoothie jar, and then, triggered by a nerve impulse, they rush out. This movement of calcium ions triggers a response in the cell. In muscle cells, it could mean the contraction of the muscle cell for movement.
In other cells, it could mean other things like maybe the secretion of a protein. Moving on to the Golgi body. The Golgi body is kind of like the warehouse of the cell.
Its purpose is to modify, package, and ship molecules to various locations around the cell. It consists of a bunch of folds called cisterna, and it has two ends, the cis end and the trans end. The cis end receives molecules to be packaged and the trans end ships them out.
So say we have that protein that left the rough endoplasmic reticulum. It would arrive at the Golgi body and fuse with the cis end. Then it would travel through the Golgi body and as it did, it would be modified with either the addition or deletion of various chemical groups. Then, once it reaches the trans end, it's shipped off again in another vesicle to wherever it needs to go.
Let's move on to chloroplasts. Chloroplasts are organelles that are only located in plant cells. They contain a substance called chlorophyll, which gives plants their green color.
Chloroplasts have one main function, to perform photosynthesis by converting the light energy in sunlight to chemical energy that can be stored in or used by the plant. Chloroplasts have a special structure to help with this. They have a double membrane, and the space between the two is called the intermembranous space because it's literally the space between the two membranes. Inside it we have a circular structure called the thylakoid.
The first part of the photosynthesis reaction occurs in the membrane of the thylakoid. Thylakoids can sometimes be arranged in stacks called grana and they also have a space inside them called the thylakoid space. The rest of the inside of the chloroplast is called the stroma. This is where the second part of the photosynthesis reaction takes place.
And what's interesting is chloroplasts have their own ribosomes and DNA, which are located in the stroma. And that's all you need to know about chloroplasts. Next, we have mitochondria.
Mitochondria have a very similar structure to chloroplasts. They also have a double membrane, so there's your layer 1 and 2. Their second layer has many folds in it called cristae. They also have an intermembranous space like chloroplasts, as well as their own ribosomes and DNA, which are located in a region called mitochondrial matrix. Similarities between chloroplasts and mitochondria actually extend beyond structure. Both of them are involved in the conversion of energy.
While chloroplasts convert light energy into chemical energy, mitochondria serve to convert the chemical energy from your food into ATP, which is an energy currency. that your cells can use to perform different tasks. So mitochondria kind of perform the opposite function of chloroplasts. And this process of cellular respiration occurs in the inner membrane, and that's why those folds are there, so there's more surface area for this process to occur, and more energy is generated quickly.
And that's all you need to know about mitochondria for now. Next, we have vacuoles. Vacuoles are basically just storage containers. They are a... a membrane-enclosed area that can store food, water, waste products, and more.
An example of a vacuole would be the central vacuole in plant cells. This vacuole mainly stores water and inorganic ions like potassium and chloride ions. Only plant cells have a central vacuole like this. Animal cells have smaller vacuoles sparsely scattered around the cytoplasm to store different substances.
Moving on to our last or organelle, lysosomes. Lysosomes are organelles that contain enzymes to digest molecules. So say I have a vesicle with a food molecule in it, and there's my lysosome. The two will fuse with each other and their contents will mix, so the enzymes in the lysosome end up digesting the molecule. Lysosomes can also be used to digest food molecules.
So I have be used to digest or get rid of non-functioning organelles. So say if I had a mitochondria that wasn't doing its job well, then my lysosome would digest it to get rid of it because it's just using up resources and not providing me with a product or an outcome. So there you go. Now you know all of the major organelles, their structures, and their functions.
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