Cell Organelles
The cell is the most basic functional and structural unit of life. It is incredibly tiny - 7 to 8 cells could fit in the width of a single strand of hair! Cells make up everything in us, from our fingernails to tissues and organs.
Some organisms are made up of just one cell and called unicellular (one-cell) organisms. Other organisms, like us humans, have trillions of cells in our bodies. The largest creature on earth, the blue whale, has approximately 100 quadrillion cells.
A cell is like a water ballon in that it holds water (and many other molecules and structures) inside of it.
There are three domains of organisms generally agreed upon: prokaryotes, eukaryotes, and bacteria. I shall mainly focus on prokaryotes and eukaryotes.
Prokaryotes are microscopic organisms belonging to the domains Bacteria and Archaea. They look like the character Plankton from SpongeBob - like a capsule with antennae.
Eukaryotes are organisms belonging to the domain Eukarya and include plants, animals, and fungi.
Despite how tiny cells are, they have structures inside of them called organelles which are much smaller than cells themselves. There are various organelles inside a cell, and they all have different functions that enable the cell to survive. Although prokaryotic and eukaryotic cells have different organelles for the most part, they share a couple of the same ones.
Within eukaryotes, plant and animal cells mainly share the same organelles but have plant cells have some exclusive to only plants. We'll go into it in depth!
Everything listed below is found in both plant and animal cells unless listed otherwise. These drawings are extremely simplified, and just for understanding. The majority of the organelles look and behave the same in both plant and animal cells, and I'll provide close-ups of them from the previous picture of the cells.
Chloroplast - Found exclusively in plants! It is an organelle that conducts the process known as photosynthesis (turning carbon and water into sugar for the plant (and oxygen as a byproduct)). Photosynthesis is a complex process that will have its own lesson. For now, all you need to know is that only plants have a chloroplast.
Nucleus - This is the 'headquarters' of a cell. The nucleus houses the cell's genetic code, the DNA. Replication of the DNA will take place here. The nucleus also regulates the cell's functions (gene expression, cell replication, growth). The nucleus has a double membrane and is one of the only organelles to have this (the others being the mitochondria and chloroplast).
Nucleolus - a spherical region located inside the nucleus. It has a lot of RNA and proteins and creates ribosomes. There are no chromosomes here.
Golgi Body/Golgi Apparatus - Think of the Golgi Body as a post office - it's responsible for transporting, modifying, and packaging proteins/lipids that come from the Endoplasmic Reticulum, similar to how a post office sorts, packs, and distributes mail. It also is involved in the creation of a lysosome.
Lysosome - the garbage receptacle of the cell. Found in both animal and plant cells, but more so in animal cells. The lysosome can store and transport molecules, as well as digest discarded molecules using hydrolytic enzymes (the lysosomal membrane pumps H+ ions into the lysosome, creating an acidic environment to digest molecules), whose product can then be recycled as used again. Lysosomes can also make a cell commit suicide! If their membrane is damaged and allows the H+ ions to leak into the cell, the cell will die because its internal environment is now acidic.
Apoptosis - the programmed destruction of cells in a multicellular organism. This is useful in the development of hands in the womb - a fetus's hand will undergo apoptosis to develop fingers.
Vacuole - used for storage and transportation. In plants, vacuoles also take on the job of the lysosome (sometimes even called the plant's version of the lysosome). Something called the central vacuole is found in plants only. It's an extremely large vacuole that stores water.
Rough Endoplasmic Reticulum (RER) - Makes proteins that will leave the cell because of the ribosomes bound to its exterior. These include receptor proteins and protein channels for the cell membrane.
Ribosome - a protein that makes proteins and is used during translation of proteins. It has 2 subunits: the large and small subunits. There are two types of ribosomes.
- Bound ribosomes: bound to the outside of the RER. They synthesize proteins that will leave the cell.
- Free ribosomes: suspended in the cytoplasm. They synthesize proteins that will stay inside the cell.
Smooth Endoplasmic Reticulum (SER) - Makes carbs, lipids, and phospholipids.
Mitochondria - Powerhouse of the cell: this is where ATP (Adenosine TriPhosphate) is made, the most common molecule used as a source of energy.
Cell membrane - Made up of a phospholipid bilayer (remember this from our previous lesson?). It is semi-permeable, meaning that select molecules can pass through while other molecules will need help to pass through. Later, we'll go into which molecules can pass through and which need help to pass through. This membrane creates a barrier between the outside and inside of the cell, keeping all organelles inside and safe. It is also quite flexible.
Cell Wall - tough and flexible material covering the outside of only plants and prokaryote cells. When the central vacuole swells with water in a plant cell, the cell wall is important in not allowing the cell to burst and keeps its shape. In plants and algal (algae) cell, the cell wall is made up of cellulose. In fungi, it is made up of chitin. In bacteria, it is made up of pectin - the stuff that makes jelly jelly!
Cytoskeleton - a network of protein filaments that support the structure and shape of the cell and helps with cell movement. It is found inside the cell throughout the cytoplasm. In the photo below, it is the pale purple lines all over inside the cell. If it's hard to see, you can always click on the picture and zoom in.
Cytoplasm - the cytoplasm is a jelly-like substance inside the cell that has nutrients and holds organelles in their place. It is made up of cytosol, which is mainly water.
Centriole - found only in animal cells! These organelles only come into being when the cell is going to start replication. It is used in cell division to make sure the DNA is spread evenly between the daughter cells (more on that when we cover mitosis and meiosis)!
That was a hefty lesson! Now for the joke:
Why are there gates around cemeteries?
Because people are dying to get in!
(haha)
The images in the pictures are a bit fuzzy. I'm not sure if you can fix that but if not its still readable. Thanks for the great lesson!
ReplyDeleteIn the next lesson where you talk about membrane proteins, you showed one here in the cell membrane picture. That would be a peripheral protein, right?
ReplyDeleteNope! It would be an integral protein - see how it extends all the way through the membrane, with a tube or empty area going through it? That means it's an integral protein because it'll transport molecules from outside the membrane to inside the membrane, through that tube. Peripheral proteins don't typically extend all the way through the membrane and will kind of loosely lie on top of the membrane, and will not have a 'tube' going through it as they don't transport anything. Hope that helps!
DeleteWhy’s the mitochondria so wrinkled on the inside?
ReplyDeleteHaha, I was about to publish a lesson on that! The reason for the wrinkles is to get a higher surface area to volume ratio. The mitochondrion has a double membrane, like this: outside mitochondria | intermembrane space | matrix (each '|' is a membrane). The inner membrane which separates the intermembrane space and the matrix has proteins needed for the Electron Transport Chain (ETC) (we'll learn this in depth when I cover cellular respiration). Now, the more wrinkled the mitochondria is on the inside, the more surface area it will have, meaning it will have more ETC proteins needed for cellular respiration (gaining energy). The more energy it makes, the more successful it, and the cell, is. When I post the lesson on this, there'll be photos to demonstrate this concept better. Hope that helps!
DeleteDo bacteria have a cytoplasm?
ReplyDeleteYup!
Delete