What is turned "off" and "on" DNA?

Question

Why DNA turned "off" and turned "on"? Is there any limited number that should be turned on? If one of my DNA is turned "off" right now, then what is the probability that that DNA will turned "on"? What is this process, why we have this process, how this process works, where this process works, and which way this process has conclusion? Please help me understand this process, I am bilingual so please do not use hard English words.

Answer 1

Not all genes are transcribed in all tissues or at all times: Gene expression is regulated both temporally and spatially. Gene expression can be regulated at several levels (transcription, splicing, export, translation, post-translation, etc.), but the most efficient is at transcription. It you want to express the gene then transcribe it. If you don't want to express the gene then don't transcribe it.

Regulating transcription can happen several ways such as inactivating transcription factors, repressor proteins, or DNA "condensation". DNA that is condensed cannot be transcribed because Pol II cannot access  the ORF. To permanently condense (or heterochromatinize) DNA enzymes add methyl groups to the DNA and/or add acetyl groups to the histones. This prevents them from releasing and therefore prevents transcription. DNA that is highly methlyated or acetylated is condensed and inactive, and is frequently referred to as being "off". Methylation tends to be permanent, but acetylation can be reversed.

A good example is X Inactivation.

Answer 2

Turned "on" or "off" DNA refers to wether or not the DNA is active.  To put it simply, when DNA is packaged or coiled, it is inactive, because the various sites needed to activate transcription are hidden.  When the DNA opens up or uncoils, it is active, because transcription factors and other replication machinery have access to the DNA.  

Answer 3

Every embryo began with its entire genome (all of its genes) 'ON' or unaltered by regulation. This means for the first few divisions each cell could become a separate person, a twin or quadruplet. After this point there are changes in the embryo's DNA that make the cells different from each other, some genes are down regulated or turned permanently 'off'. This is the start of skin, nerve & connective tissue, all the different types of cell lineages. Skin cells do not need the same set of genes to be skin that blood cells do, so skin cells (epidermis cells) have all their non-skin genes down regulated, turned 'off'. Connective tissue cells have skin genes down regulated. This is called differentiation.

http://en.wikipedia.org/wiki/Cellular_di...

The more a cell divides the more the DNA accumulates changes. Daughter cells differ from the parent cell as the cell differentiates or specializes in its job in the body. A few cells of each type remain as stem cells to produce new specialized cells even in the adult. Blood stem cells reside in the bone marrow and are the parent cells for all the circulating red & white blood cells.

While a child is growing there are many more types of stem cells. Some of each type of tissue to grow into all the organs in a developing body. They 'know' where they are in the body by signals from their surrounding cells. These signals from the surrounding cells in an organ help each stem cell to down regulate to the next level of specialization that is needed for that organ. Cells cooperate to grow into the organ they belong to. This is how they 'know' which gene's to turn off and the specific way to turn them off in this organ.

http://stemcells.alphamedpress.org/cgi/c...

Answer 4

It doesn't mean the entire strand of DNA is turned on and off. I forgot what it was called check it out on wikipedia but certain parts of a strand of DNA are turned off when a baby is developing.  

For example just say a strand of DNA was being made for a white blood cell. A white blood cells role is to defend against intruders so the DNA strand would turn on a certain part of its sequence whilst developing to make sure the DNA strand develops to do that task. (And obviously through mRNA DNA strands multiply though the triplet codes)

So the DNA strand cannot turn on and off whenever needed but as an embryo develops parts of a DNA strand are turned on and off to specialize a cell.

Now if a DNA strand has all of the possible speciality functions switched on that makes that DNA a possibility for a stem cell as it hasn't yet been specialized.

Answer 5

DNA is neither turned on or turned off. It is a blueprint. DNA consists of amino acids. Within the DNA are found genes. It's these genes that are either on or off, depending on the traits you inherit from your parents.  If both parents have a certain gene that is on, then you will inherit the gene in the "on" position.  If one parent has a gene that's on and the other has the same gene that's off, you have a 50/50 chance of inheriting the gene in either position (on or off).  If a gene is off, the only thing that will turn it on is a mutation or a chemical activator that is artificially applied to it. Genes do not turn on and off by themselves.  Genes determine traits (such as eye color, hair color, height, predisposition to certain diseases, left or right handedness, etc...)