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Cell Biology

Learn the toughest concepts covered in Cell Biology with step-by-step video tutorials and practice problems by world-class tutors

7. Gene Expression

Basics of Gene Expression Control


Gene Expression Control Basics

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Hello everyone in this lesson. We are going to be learning about cell differentiation and gene expression And specifically we are going to learn about how cells can have different fates and different jobs depending on the genes that they express. Okay everyone. So gene expression is the process through which cells selectively choose to express some jeans and not others. Now this is going to be important because gene expression is going to be where these cells choose which genes to express and which ones not to express. And this is important because every cell in a multicellular organism is a clone. Every cell in your body has the exact same genetic match material as every other cell in your body. They are all clones but they don't all do the same thing. So the way that you are able to have specialist cells tissues, organs and body structures is because of this gene expression and it is going to be unique to each type of cell. So the difference appearances and functions depend on so selectively expressing certain genes and not others. There are genes in your cells that are purposely built for liver function and only liver cells are going to express those genes. Your eyeball cells are not going to express your liver genes. Only the liver cells are going to do that. So while you have the gene information to do everything, certain cells are only going to express the correct genes so that they do the correct job. So gene expression controls the expression of proteins and RNA is basically it's going to control the gene products and cell differentiation is the process by which a cell becomes specialized for a particular function. Self differentiation is very important because it's going to allow us to have all of our unique cell types. And differentiation is entirely directed by gene expression control. Gene expression control can come in many different forms but it's basically regulating the products that are made in a particular cell from the D. N. A. Which genes are transcribed which which ones are translated how the M. RNA is created, what exons are chosen to be put in that M. R. N. A. How the proteins are made, how the products of those genes function. And if they are made at all. So this allows for multicellular organisms to have a wide array of unique and diverse cell types. So an example of this can be seen here and differentiation of a stem cell into many blood cell types. So you can see here we have a multi potent Hemmat poetic, I believe, stem cell. So it's multi potent meaning that this particular cell can make any type of blood cell that it needs to. And these are going to be found in the bones generally and you guys can see it makes all of these different types of cells which have a wider range of characteristics, sizes and jobs basically you guys can see over here we have our lymphocytes and these are going to be your immune cells and you have your natural killer cells. You have your small lymphocytes, your T cells, your B cells, your plasma cells. These are going to be very important to maintain your health, your innate immune system and your adaptive immune system. And they all come from these multi potent stem cells. This multi potent stem cell for blood is also going to make all these other cell types. So this particular giant cell here is going to make platelets. So it's a platelet cell. You guys can see here we have the red blood cells which are also called Aretha sites. You have these mast cells which are going to be important for making histamines. And then all of these down here are going to be your white blood cells. So you guys can see that all of these different cell types of blood cells because there are many, many different types of blood cells all came from this cell right here and all of these cells have the exact same genetic material but they don't do the exact same job. They don't even look the same. And that is because they choose to express certain genes that unique to their function. And this is cell differentiation and cell specialization based on which genes they express, which genes they transcribe and translate everyone. So let's go down and let's continue our talk of this lesson. Okay, so gene expression can be can be controlled at various steps in the r in the DNA to RNA protein pathways. So there are many steps and many actions that our cells can take to control gene expression. Most people think it only happens at the transcription level. That gene expression either happens or does not happen because an M. R. N. A. Is made. While that is a very major me major step in gene expression, it is not the only step that controls gene expression and you can also have the control of gene expression of course at transcription. Whether that M RNA is made or not, you can have it happen at RNA splicing or RNA modification whenever that M RNA is being matured. You can have it happen in translation. You can have it happen at many many different air areas and times. And gene expression can be controlled by external signals as well. And these external signals can be things like hormones. You can have certain hormones that are going to tell certain cells to do certain things like sex hormones will tell excels to be created or sperm cells to be created. You can also have external signals like cold temperatures and less sunlight. And in some animals this is going to trigger some of their cells to begin secreted hormones or begin differentiating into sex cells because it may be mating season. So you can have environmental factors, hormonal factors. External factors that can control this differential expression. Not just these genetic factors. All right, but there is an exception to this. There are some some cells. Sorry, some genes there are some genes which are always used in all of the cell types. And these are going to be called housekeeping genes. And the reason that a cell doesn't get to choose whether expresses these genes or not is because they can't live with about these jeans. These are going to be jeans that are used in every cell because they are critical for life. So these cells don't get to decide. They don't get to differentiate whether they want to express these genes or not. They have to And these are going to be things like ribosomes. All genes are in a preliminary genes. DNA repair genes, histone genes, histone genes, Uncle gene's transcription factors, genes, cell cycle regulation genes. All of these have to be expressed in every cell or the cell either won't create proteins. It won't make M R N. A. It won't divide correctly. So, there are a set of genes that every cell is going to express. But a lot of the genes in our cells are going to be unique to particular jobs that a cell might have. Alright, so let's go down, let's scroll down a little bit and this is going to be just a representation of kind of what we've already talked about. This is going to be the many ways. In many locations that gene expression can be controlled because there are many steps in this pathway to the crew creation of a gene product in which it can be controlled. So obviously we have our gene up here and it is either going to be expressed or it's not going to be expressed in the first level of expression. Control is going to be transcription. All control. You can allow transcription to happen. You might not allow transcription to happen. This can be controlled by histone modifications. This can be controlled by methylation of the DNA. Which is going to cause it to not allow replication machinery or transcription machinery to bind to it. You can have genes being hetero croton where they're so tightly wound. Then RNA polymerase can't even get into that gene to express it. These would be things called transcription control. You can also have repressors. Okay guys so basically transcription all control is basically is this gene able to be transcribed. Yes then it's probably going to be transcribed. Know that we're not expressing that gene. So and there's many ways you can control that expression. Okay now you can also have RNA processing. So let's say that you have made the M. R. N. A. U. You can have things like differential splicing. Where say there are three exons in a gene but you only choose to put two of them in the M. R. N. A. Then you're going to make a very unique protein. There are different ways that you can change the M. RNA to make a unique protein for a unique function which is going to change the gene expression and then you can have things like RNA transport. Where are these RNA is going to be transported in the cell so that they can be translated because where they are translated is going to depend where their job is going to be, where they are going to be transported. Remember they can be translated all over the cytoplasm but they can also be translated in the rough into plasma articulate and then they can be transported in or out of the cell. So where it is translated is very important as well. And then of course you're going to have translational control is the M. RNA even allowed to be translated. It might not be, it might be degraded before it even translated. And then technically that gene wasn't expressed because the protein product was not made. So as you guys can see there are tons of different ways that you can control expression. The transcription control is going to be the most common and this is because it requires the least amount of energy. But all of these other processes do happen. You can control gene expression in transcription. RNA processing. RNA transport and translation in every step of expression of a gene. But just remember guys that gene expression is going to determine the type of gene and the the type of cell and the function that that cell has and we call this cell differentiation when it chooses to express certain genes that are important for its way of life and its job in the multicellular organism. Okay, everyone, I hope that was helpful. Let's go on to our next topic.

Gene expression is defined as which of the following?


Every gene is regulated differently in each cell type.