DNA


 * Branched DNA

DNA fraying occurs when non-complementary regions exist at the end of a complementary double-strand of DNA. However, when branched DNA occurs, a third strand of DNA is introduced and contains adjoining regions able to hybridize with the frayed regions of the pre-existing double-strand. Although the simplest example of branched DNA involves only three strands of DNA, some complexes involve additional strands, with multiple branches also being possible. An example where Branched DNA is highly used is in nanotechnology to construct geometric shapes. **


 * 1) [|htt][[image:file/view/DNA_trancription_and_translation.jpg width="114" height="138" caption="DNA transcription and translation at the same time" link="http://www.accessexcellence.org/AE/AEC/CC/DNA_structure.php"]][|p://ww][|w.howst][|uffworks.com/search.php?terms=dna] this links gives alot of information on several areas envolving DNA
 * 2) []
 * DNA is a long polymer made from repeating nucleotides. The DNA chain is 2.2-2.6 nanometers wide.
 * In 1951, the then 23-year old biologist James Watson traveled from the United States to work with Francis Crick, an English physicist at the University of Cambridge. Crick was already using the process of X-ray crystallography to study the structure of protein molecules. Together, Watson and Crick used X-ray crystallography data, produced by Rosalind Franklin and Maurice Wilkins at King's College in London, to decipher DNA's structure. James Watson, Francis Crick, and Maurice Wilkins recieved the Nobel Prize in medicine for thier work with DNA in 1962. Both James Watson and Francis Crick are shown below in the following two pictures.

(These images were from: [] and [])

code The main stabilizing factor that hold two DNA strands together is the base stacking: the hydrophobic effect, van der Waals and dipole dipole interaction. Base pair Hydrogen bonding is less important than stacking in stabilizing double stranded structures. code
 * The topic of this Wiki is Deoxyribonucleic acid, better know as DNA. DNA can be thought of as the blue print of life, its what makes all organisms unique. DNA is made up of four nitrogenous bases; adenine, thymine, guanine, cytosine which pair up together, adenine with thymine, and guanine with cytosine, each base is also connected to a sugar and phosphate molecule. These bases are what makes the DNA strand into a double helix molecule which resembles a spiral staircase or twisted ladder.

Of the four nucleobases found within DNA, adenine and guanine are derivatives of the aromatic organic compound purine, while thymine and cytosine are derivatives of the aromatic organic compound pyrimidine. All of the four nucleobases are composed of an alternating deoxyribose sugar and a phosphate group(the actual nucleobases are bonded to the deoxyribose sugar).



Within RNA, the nucleobase uracil replaces thymine, which is in fact a methylated version of uracil. The methylation of uracil within DNA provides structural support and additional efficiency during replication.




 * Base Pairing**

DNA strands are paired together by hydrogen bonding between nitrogenous base pairs. Each base is bonded to a deoxyribose molecule which is bonded to other deoxyriboses via phosphodiester bonds. These are what hold each individual strand together. Complementary strands are held together by the hydrogen bonds. Adenine and thymine are paired together using double hydrogen bonds, while cytosine and guanine are paired by triple hydrogen bonds. The triple bond is more stable, requiring more energy for the separation of cytosine and guanine. You can see both these double and triple bonds below. Also, you can see the structure of DNA and DNA's sugar-phosphate backbone.

(This image was from: [])
 * DNA Melting**

//DNA melting//, or //denaturation// occurs when DNA strands are separated into single strands. This can be caused by heating or exposure to denaturing agents. The melting temperature (Tm) refers to the temperature at which half exactly of the base pairs in a double-stranded DNA molecule will be broken. Concurrent with what is stated above, the more G-C pairs in a DNA molecule, the higher the melting temperature for that DNA molecule.


 * DNA Function**

There are four requirements for DNA and the genetic information that follows:
 * 1) Storage of information
 * 2) Replication
 * 3) Expressing information
 * 4) Variation by mutation

To further expand on this, first and foremost, DNA is the storage center of all of the genetic information, which is why it is described as being the blueprint for life. When cells enter mitosis or meiosis, they look to the DNA to see how the copy should be made. Secondly, DNA must replicate this information when cells undergo meiosis and mitosis. Next, this information is expressed in the individual as genes. These genes are then shown in the physical form as the organism's phenotype (e.g hair color, eye color). Finally, there can be a mutation in the DNA which could alter how the gene is expressed. This mutated DNA could also be passed on from parent to offspring.

James Watson and Francis Crick were credited with discovery of the structure of DNA. They were not the only scientists working of finding the structure. Rosalind Franklin and Maurice Wilkins were working as well. Franklin was using X-ray diffraction to help find the structure. Wilkins showed one of Rosalind's best diffractions to Watson and upon seeing this Watson and Crick were quickly able to construct a model for DNA.
 * Discovery of the structure**

Central Dogma of Molecular Genetics
 * In the transcription of DNA, three main types of RNA molecules are synthesized: messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA).
 * Of these, mRNA's are translated into protiens. Each mRNA is the product of a specific gene and directs the synthesis of a different protein.
 * Translation occurs in conjunction with ribosomes and involves tRNA, which adapts the chemical information in mRNA to the amino acids that make up protiens.
 * These processes (DNA is copied to form new DNA; DNA is transcribed to make RNA;and RNA is translated to construct proteins) form what we call the Central Dogma of Molecular Genetics.
 * One exception to this process is utilized by retroviruses, such as HIV. Retroviruses carry their genetic information in the form of RNA. They inject the RNA into host cells, along with an enzyme called reverse transcriptase. The reverse transcriptase acts to transcribe DNA from RNA. The new DNA is then used to hijack the cell to produce more copies of the virus, which move on to attack more cells.


 * DNA replication**
 * DNA is replicated via the unzipping the double helix and pairing the new chemical bases (neucleotides) with their proper bases.
 * DNA Polymerase is the enzyme that synthesizes the new DNA
 * DNA Mutations[[image:file:///C:/DOCUME%7E1/OWNER%7E1.YOU/LOCALS%7E1/Temp/moz-screenshot.png]]**
 * A mutation is described as any random, permanent change in a DNA molecule. While most mutations are detrimental to the organism, some have no effect on the DNA, and a few are even beneficial. Nature is then able to use the beneficial mutations to help organisms to evolve and thrive, such as the changing of a bird's beak so they are more able to readily eat the hard to extract seeds.

The first thing that happens in DNA replication is that the two strands that make up the structure of DNA are unwound from eachother. DNA helicase opens a short segment of the helix. The point where this is opened up at is called the replication fork. DNA polymerase goes along each strand and adds the reciprocal sequences of the DNA. If the side being replicated is GCA then the strand being created will be CGT. This process occurs in opposite directions. So, in one strand the bases are being added toward the replication fork and the other is replicated from the replication fork. On one strand that is moving toward the replication fork the bases are being added in a new long strand of DNA that compliments the old strand. The other strand of DNA, the one where the bases are added away from the replication fork, are only added in short segments along the strand. This occurs because DNA polymerase can only replicate going in the 3' dirrection. These segments are called Okazaki fragments. These fragments are joined together by an enzyme called DNA ligase. This process creates two daughter strands of DNA. This is the semi-conservative replication. Two illistrations of DNA replication can be seen below. (Pictures were taken fromhttp://kvhs.nbed.nb.ca/gallant/biology/replication_fork.jpg and [])

Due to the expansive length of DNA and its relatively tight storage area within the nucleus of eukaryotic organisms, a complex method of condensing DNA for storage is employed by way of bead-like proteins called histones. Approximately 200 base pairs of DNA are coiled around an eight-histone complex, forming a structure called a nucleosome. Nucleosomes are then coiled together and form the repeating units of chromatin, which is then supercoiled to form a single chromosome. As chromosomes must expose gene rich segments for transcription chromatin possesses the ability to unravel into a lightly packed structure referred to as euchromatin. The alternative tightly packed chromatin of chromosomes is conversely referred to as heterochromatin.

Here is a video of DNA Structure. It is very easy to understand! [|DNA Structure]

Here is a great video about DNA transcription and protein assembly: []#

A beneficial video about how DNA replication works: http://www.youtube.com/watch?v=4jtmOZaIvS0

A valuable video on DNA fingerprinting: []

A quick video on DNA damage and repair: []

A helpful video on DNA mutations: []

A very useful game to help comprehend DNA replication: http://www.studystack.com/matching-159604

Here is a picture of DNA and its four base pairs and phosphate sugars. This shows the double helix form that DNA takes. This picture was taken from [].

Sadly, DNA can be damaged/ mutated which can cause problems in a individual or even death. There are two main ways that DNA is altered and damaged. The first way that DNA is altered is from environmental agents. These agents are, but no limited to, ultraviolet light, smoke, radation, and chemicals. These are just a few examples of many things that can cause cancer or unwanted mutations. The second way that DNA is altered is by cell replication mistakes. When a cell starts replication and trys to make new copies mistakes can happen. This can also cause unwanted mutations.

Here is an example of a mutated DNA sequence.

This picture was taken from [].

There are many things that can go wrong with DNA replication. Mutations can arise and here's a Youtube video showing what can happen. http://www.youtube.com/watch?v=Luw5_z8mIrI&feature=PlayList&p=40A6C1FF95C70259&index=3&playnext=3&playnext_from=PL.

Here is a simple, labeled structure of DNA.

The genetic make-up of individuals is sometimes more alike than most of us would think. Humans are not only closely related to primates, but our genetic sequence is close to some insects as well. There's also 'Junk' DNA. The more complex the organism, the more important junk DNA seems to be. This is still being studied, but so far, there has been significant evidence to support this claim. (this information was found at http://sciencenow.sciencemag.org/cgi/content/full/2005/714/4)

Genome- genome is an organisms complete set of DNA which includes all of its genes. For humans a complete genome is over 3 million base pairs, and they are contained within all cells that contain a nucleus. The Human Genome Project was an international project to identify the sequence of the human genome and to identify the genes it contains.

Here is a video to help better understand genome http://www.youtube.com/watch?v=Zxv2HS1EhlI