Cell Function

Hey guys, welcome to this Mometrix video over Cell function. In our last video we looked the structure of a Eukaryotic animal cell. We looked at the main components of a cell, and what those components are made of. In this video we are going to look at the function of all of those components; so, what do all of those things do?

Cell Membrane

In our last video I mentioned that the cell membrane works to separate the intercellular from the extracellular, but it does a lot more than that. The cell membrane is a semi-permeable phospholipid bilayer. Semi-permeable means that some things can pass, and others can’t. So, the cell membrane is kind of like security at an airport. The lipids in the cell membrane function to give the cell flexibility, while the proteins in the cell membrane work to supervise and maintain cell’s chemical atmosphere. The proteins also help to transfer appropriate or “authorized” molecules across the cell membrane. So, the cell membrane functions both as a structural component and as a protective or security component.

Nucleus

The nucleus houses most of a cell’s genetic information. DNA is packed into the nucleus, along with several other proteins, which form chromosomes. The nucleus kind of works as a security vault for a person’s hereditary information, but it also controls all of the functions within a cell by regulating gene expression. The nuclear genome of a cell is what promotes cellular function. The nuclear pores within the nuclear membrane are impermeable to larger molecules, so the nuclear pores work to selectively channel into the nucleus, from the cytoplasm, the necessary proteins and RNA. The nucleus is often referred to as the cell’s brain or control center.

Nucleolus

The nucleolus is housed within the nuclear membrane of the nucleus. I said that the nucleus is like the brain of the cell; well, the nucleolus is like the brain of the nucleus. The nucleolus is where ribosome biogenesis takes place, and ribosome biogenesis just means the making of ribosomes. The nucleolus also helps in forming signal recognition particles which aid our body’s response to stress.

Cytoplasm

So, the cytoplasm actually refers to everything on the inside of the cell membrane, except for the nucleus. The parts of the cytoplasm that does not contain organelles is filled by cytosol. Cytosol is that gel-like water-based solution, that fills the inside of the cell membrane and helps to give the cell its shape. The main function of the cytoplasm is to support and suspend the cell, and all of its inner organelles. The cytoplasm also allows for transportation of materials, and works to dissolve cellular waste.

Cytoskeleton

The cytoskeleton is networked all throughout the cytoplasm, and handles several essential functions. Like you might imagine, the cytoskeleton supports and helps to maintain the shape of the cell. It helps to hold the organelles in their place, and is directly responsible for the movement of organelles throughout the cell. The three components that the cytoskeleton is composed of (microfilaments, intermediate filaments, and microtubules) all have their own set of primary functions. Microfilaments are primarily composed of actin, which is a contractile protein. Microfilaments help to control cellular movements, like contraction, and cytokinesis. Intermediate filaments are a little larger in diameter and work to maintain cellular structure, and to hold tissues together (like skin for instance). Microtubules are the largest of the three components making up the cytoskeleton. As I’m sure you can imagine, microtubules are hollow tube like structures. Microtubules help to move sister chromatids (during metaphase) so that they line up in the center of the cell, provide a pathway for vesicles to move through the cell, and they help to protect the cell from being compressed.

Mitochondrion

The mitochondria is sort of like the cell’s generator, you may have heard it referred to as the cell’s powerhouse. Well, the reason they are thought of in this way is, because the mitochondria is where nutrients and oxygen are converted into energy (more specifically adenosine triphosphate {ATP}). The two membranes of the mitochondria work together to only allow specific molecules into the matrix. In the cell’s cytoplasm, sugar, or glucose, is broken down to pyruvate. Pyruvate enters into the mitochondria, and is then converted to water and carbon dioxide. From there, these compounds are converted to ATP. This energy, in the form of ATP, is what generates cellular respiration. The number of mitochondria in each cell will vary, depending on the amount of energy needed for each cell to function properly; and the cells can produce more mitochondria as needed and/or merge mitochondria together in order to form larger ones. Muscle cells, for example, can sometimes contain thousands of mitochondria.

Ribosomes

Ribosomes are formed in the nucleus. They enter the nucleolus to get the four rRNA strands that make up their two subunits. The ribosomes then exit the nucleus through the nuclear pores, enter the cytoplasm, and perform protein synthesis. Basically what that looks like is, the RNA molecules work as instruction on how to connect amino acids in a specific order, so that they can carry out their designated function. Ribosomes are heavily concentrated on the rough endoplasmic reticulum, and around the nucleus; they also are located all throughout the cytoplasm in lower concentrations.

Endoplasmic Reticulum

The endoplasmic reticulum is often referred to as the manufacturing center of the cell, because it functions to manufacture, process, and transport packages from the nucleus to be utilized within the cell. Almost everything within the lumen of the endoplasmic reticulum is sojourning (or transient), which means that it is only there for a short time before it is transported out. However, the endoplasmic reticulum needs some protein workers to be able to do its job of manufacturing, processing, and transporting. These proteins are called endoplasmic reticulum resident proteins (I know, pretty creative). These proteins contain a very specialized sequencing of amino acids that the endoplasmic reticulum is able to recognize, so that it retains these specific proteins. In our last video on cell structure we talk about the two different types of endoplasmic reticulum: Rough endoplasmic reticulum, and smooth endoplasmic reticulum. Well, these two types of ER have different functions. The primary role of the rough ER is to produce and process proteins that are needed inside the cell or outside of the cell. The rough ER works to put the proteins in their three-dimensional shape, so that they are set up to function properly.

The smooth ER works to produce lipids, creates the building blocks for carbohydrate metabolism, and works to detox the cell of drugs poisons. The endoplasmic reticulum will be more prominent in some cells than in others. For example: brain, muscle, and liver cells will all have a more extensive smooth endoplasmic reticulum.

Golgi Apparatus

The Golgi apparatus is referred to as the shipping department of the cell. It receives packages from the endoplasmic reticulum, and makes the necessary packaging additions in order to fully form functioning lipids and proteins. The proteins and lipids are transported from the endoplasmic reticulum in vesicles to the cis face of the Golgi apparatus. The vesicles attach to the cis face of the Golgi body, and then release the transported particle into the Golgi body. These phospholipids, proteins, carbohydrates, and other molecules that are composed inside of the endoplasmic reticulum get transported to the Golgi body to be modified, as they are transported to the trans face to be secreted, so that they are useable (or functional). The Golgi apparatus basically receives various macromolecules, makes any necessary modifications, and labels them so that they get where they need to go.

Lysosomes

Lysosomes are the guys that keep the cell community clean. They go around and collect cellular debris, and break it down with the digestive enzymes inside of their membrane. Cellular debris may mean cellular matter that is too old to function efficiently, or really anything in the cell that is not useful to the functioning of the cell. Lysosomes are typically found in greater number within white blood cells, because white blood cells need to digest more unwanted material than other cells.

So, that is an overview of the function of a eukaryotic animal cell. In our next video lesson we will look at macromolecules. What are they, where do they come from, and what do they do? So, be sure to check it out.

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See you guys next time!