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Transcript of 2.03 Biology
By: Wesley Cates
Above is a broad diagram of a eukaryote cell.
We'll start out at the cell membrane.
The cell membrane is a barrier around the cell,
The membrane is a selective barrier, meaning that it can let in certain things and block out other things. This allows nutrients into the cell, and keeps things such as bacteria out. The membrane also allows waste products to pass out of the cell. Each organelle in a cell also has their own membrane. These membranes are all selective barriers as well, determining what can enter and leave.
Next, we have the cell wall.
The cell wall is a component of a plant cell,
and it is not found in animal cells. The cell
wall surrounds the membrane and creates an extra layer of protection for the plant cell. The cell wall also helps the cell maintain it's shape and prevent over intake or loss of water.
Next, we have the mitochondria.
Each mitochondria has 2 membranes, one smooth, and one jagged. The mitochondria act like the cell's digestive system, taking in nutrients and breaking them down. Cellular respiration also occurs in the mitochondria, which takes molecules like glucose and breaks them down into forms of energy that the cell can use. Every eukaryotic cell has at least one mitochondria, but most have hundreds or even thousands. The amount of mitochondria in a cell depends on how much energy the cell needs. If the cells requires a lot of energy, it will have a lot of mitochondria, because it will require a lot of energy. Mitochondria can also reproduce if the cell is not getting enough energy.
After that, we have the chloroplasts.
Chloroplasts are found in plant cells, but they cannot be found in animal cells. They contain the green pigment chlorophyll, which gives them their green coloring. They are protected by two membranes, and also have a system of membranes flattened to make surface area. Chloroplasts are important to the cell because they convert sunlight into energy that the cell can use. This is called photosynthesis. They use energy from the sun to make glucose, which is then turned into energy.
Now we have the vacuoles.
Vacuoles are sacs surrounded by membranes, that are used for storage for a large number of things. Food vacuoles are used to store, as you could probably guess, food and nutrients for the cell. Water vacuoles are used to store water, minerals, and ions. Vacuoles and vesicles are both sacs surrounded by membranes, but vacuoles are larger. In plant cells, there is usually one main vacuole that takes up to 80% of the cell volume. Since most plant cells don't have specialized lysosomes, the main vacuole also serves as storage for enzymes too.
Now we have the lysosomes.
A lysosome is a membrane sac that holds enzymes. The enzymes are used to break down large molecules, so that they can be used by the cell. A cell has many different lysosomes that each store a different type of enzyme. Each different enzyme also breaks down a different type of macromolecule. A lysosome is a acidic environment for the enzymes to break down the macromolecules without disturbing the rest of the cell.
Next, we have the Golgi apparatus.
The Golgi apparatus is made up completely of membrane sacs. Transport vesicles carry proteins from the endoplasmic reticulum to the Golgi apparatus to be modified and/or stored. The vesicles transporting proteins to the Golgi apparatus are attached to the membrane of the Golgi apparatus, meaning that the membrane can still decide which proteins to let into the Golgi apparatus. At the other side of the Golgi apparatus, vesicles will form and be closed to carry materials to other parts of the cell as needed.
After that we have the smooth endoplasmic reticulum.
The smooth ER does not have any ribosomes on it's membrane. It's functions can vary depending on the differences of the cell it is located in. The smooth er makes lipids, breaks down carbohydrates, and detoxifies substances that may be harmful to the cell.
Now we arrive at the rough endoplasmic reticulum.
The rough ER appears rough on a microscope because it's surface is covered with small ribosomes. The ribosomes synthesize proteins, and the membrane keeps those proteins separate from the rest of the cell. In addition to making and storing proteins, it also creates it's own proteins and phospholipids to put in it's membrane. Portions of the rough ER's membrane are closed to form sealed sacs called transport vesicles. These vesicles carry the proteins to the Golgi apparatus.
Now, we are at the endoplasmic reticulum.
The endoplasmic reticulum is a 'maze' of membranes, that is so long it makes up more than half of the total membranes in the cell. It is broken down into two sections of ER that differ in both structure and function.
Next, we're at the ribosomes.
The ribosomes are the locations for protein synthesis inside a cell. Ribosomes are generally accepted to be the smallest organelle in a cell, and appear as small dots on a microscope. They are made in the nucleolus, and are found in two different locations in a cell. Free ribosomes are found separated in the cell's cytoplasm, while bound ribosomes are found attached to other organelle in the cell called the rough endoplasmic reticulum. Ribosomes are actually two different parts, attached together with protein chains. All ribosomes have the same job; to synthesize proteins. Genetic information is collected from the cell's DNA, and is transferred through RNA to the ribosomes. Construction of large protein molecules occurs here. Next, the protein is then transferred to the areas that need them. Cells with large output amounts of protein have more ribosomes than other cells. Free ribosomes usually make proteins to be used inside the cytoplasm. Bound ribosomes tend to make proteins to be used in construction of membranes or in other parts of the body.
Now, to learn about the cytoplasm and cytoskeleton.
Cytoplasm is made up of a mixture of water, dissolved salt, ions, and organic molecules. It is the liquid that fills up all the space in a cell not filled by an organelle.
The cytoskeleton is a network of fibers running through a cell, helping it hold it's composure. The cytoskeleton, very much like our own skeleton, holds all the organelle in place and also can direct the movement of organelle.
Next, we have the nucleus.
The nucleus is the main point of the cell. It is very large, and is usually near the center. The nucleus holds all the DNA and genetic information for the cell. Inside the nucleus, some DNA and protein are packed together to form chromosphomes. The most visible part of the nucleus is the nucleolus, which plays a part in the synthesis of ribosomes. Some cells only have one nucleolus, while others have more. This can depend on the species of the cell, and also how grown the cell is.