Why Genes Turn On and off ?

INTRODUCTION

Human has the same number of genes and chromosomes in each cell. However the cells can be different one to each other because the cells synthesize and form  different pattern of RNA that will be expressed into specific protein. Why it can be happened? Because each cell expresses, or turns on, only a fraction of its genes. The rest of the genes are repressed, or turned off. The process of turning genes on and off is known as gene regulation. Controlling how genes are turned on and off is important in making us run our life smoothly. Serious problems can happen when a cell messes up and the wrong gene is turned on or off. The genes also can changes their expression due to the reaction to changes in their environments.

There is a simple analogy for the process of turning genes on and off is influenced by the environment for example in the rainy day we wear rain coat or use umbrella to protect our body from getting wet (the genes are turned on) and when the rain stops or we find the shelter from the rain we take off our rain coat and umbrella (the genes turned off). We can get the main points that the genes are turned on and off depend on the situation (environment) about what types of proteins are needed to yield the specific features of each cell. The external factors of environment also have the role to determine the process of genes regulation such as the mutation that can changes the pattern of expression or damage the genes expression .The suitable environment will result the appropriate genes, and the damage on it will destroy the genes ,it’s like when we fry the fish for too long ,the protein in fish will be broken and the fish can be charred.

Gene regulation is important for making us who we are. Gene regulation is a crucial part of normal development. Genes are turned on and off in different patterns during development to make a brain cell look and act different from a liver cell or a muscle cell.  Gene regulation can occur at any point during gene expression, but most commonly occurs at the level of transcription (when the information in a gene’s DNA is transferred to mRNA). Signals from the environment or from other cells activate proteins called transcription factors. These proteins bind to regulatory regions of a gene and increase or decrease the level of transcription. By controlling the level of transcription, this process can determine the amount of protein product that is made by a gene at any given time.

Objectives :

In this paper the writer would like elaborate the information about:

1.      The process of turning genes on an off

2.      The factors that influence genes turn on and off.

DISCUSSION

1.      The process of turning genes on an off

Each gene has a promoter that allows it to be turned on or off in all the right places, at all the right times. And controlling how this happens is a big part of what makes us so complex

But before we get into that, let's start at the beginning. Genes are the blueprint for making us who we are. Genes tell each cell in our body what to do and when to do it. For example, genes have the instructions for making liver cells, carrying oxygen in our blood, or helping us break down sugar. And how to they do all of this?

By making proteins. Each gene is a recipe for making a protein. And proteins are what carry out all of our body's functions like digestion, circulation, motion, etc. A large part of our body is made up of proteins. But not every protein can do every job. Proteins are specialized to do certain things like carry oxygen in the blood or recognize bacteria in our bodies. And because of this, some proteins are only needed during certain times or in certain areas of the body. For example, proteins that build bone don't need to be in our hair!

So how do the proteins know which places in the body to be? The answer is that genes are able to be turned on and off in different places and at different times. And remember that genes make proteins. So when a gene is "on", the protein is made.And this is where promoters come in. As I said promoters are what turns genes on and off. So how do they work?

We can know the process how the genes are turned on and off to produce the protein tryptophan.If the concentration of tryptophan inside the cell is low, RNA polymerase (blue) binds to the promoter and transcribes the five genes of the tryptophan operon (left). If the concentration of the tryptophan is high, however, the repressor protein (dark green) becomes active and binds to the operator (light green), where it blocks the binding of RNA polymerase to the promoter (right). Whenever the concentration of intracellular tryptophan drops, the repressor releases its tryptophan and is released from the DNA, allowing the polymerase to again transcribe the operon.

Promoters, like genes, are made up of A's, G's, C's and T's all lined up in a certain order. Promoters are usually located very close to the gene they control.Each promoter is a set of instructions for what proteins should sit on it. The cell then looks at what proteins are there and decides whether or not to read the gene.If a gene is supposed to be on, then the proteins on the promoter are set up so that the switch can be easily found by the cell. The promoter is "backlit" so the cell can find it.

The proteins that sit on the promoter and make it so the gene can be seen or not are called transcription factors . So transcription factors and promoters work together to turn a gene on (and make a protein). Or to turn a gene off (and stop making a protein). Or even to just make more or less protein.

Genes can either be on or off all of the time. Or be turned on only under special situations. How a gene is controlled is determined by these transcription factors. Some genes, called housekeeping genes, are on all the time, in every cell. So their promoter has transcription factors that keep it in the "on" position all the time.

Other genes are only needed during certain times, like fighting an infection or making more bone. The promoters for these genes have transcription factors that tell the cell to only turn them on during these times or in these places.

2.      The factors that influence genes turn on and off

1.      Transcription factors (TFs) are molecules involved in regulating gene expression. They are usually proteins, although they can also consist of short, non-coding RNA. TFs are also usually found working in groups or complexes, forming multiple interactions that allow for varying degrees of control over rates of transcription.In people (and other eukaryotes), genes are usually in a default "off" state, so TFs serve mainly to turn gene expression "on". In bacteria, the reverse is often true, and genes are expressed "constituitively" until a TF turns it "off". TFs work by recognizing certain nucleotide sequences (motifs) before or after the gene on the chromosome (up- and downstream).

2.      Epigenetics involves genetic control by factors other than an individual's DNA sequence. Epigenetic changes can switch genes on or off and determine which proteins are transcribed. Gene silencing is a general term describing epigenetic processes of gene regulation. Within cells, there are three systems that can interact with each other to silence genes: DNA methylation, histone modifications, and RNA-associated silencing

3.      Environmental Influences on Gene Expression.The expression of genes in an organism can be influenced by the environment, including the external world in which the organism is located or develops, as well as the organism's internal world, which includes such factors as its hormones and metabolism. One major internal environmental influence that affects gene expression is gender, as is the case with sex-influenced and sex-limited traits. Similarly, drugs, chemicals, temperature, and light are among the external environmental factors that can determine which genes are turned on and off, thereby influencing the way an organism develops and functions.