The first photographic evidence of this shape was obtained in , when scientist Rosalind Franklin used a process called X-ray diffraction to capture images of DNA molecules Figure 5. Although the black lines in these photos look relatively sparse, Dr. Franklin interpreted them as representing distances between the nucleotides that were arranged in a spiral shape called a helix. Around the same time, researchers James Watson and Francis Crick were pursuing a definitive model for the stable structure of DNA inside cell nuclei.
Watson and Crick ultimately used Franklin's images, along with their own evidence for the double-stranded nature of DNA, to argue that DNA actually takes the form of a double helix , a ladder-like structure that is twisted along its entire length Figure 6. Franklin, Watson, and Crick all published articles describing their related findings in the same issue of Nature in Most cells are incredibly small.
For instance, one human alone consists of approximately trillion cells. Yet, if all of the DNA within just one of these cells were arranged into a single straight piece, that DNA would be nearly two meters long! So, how can this much DNA be made to fit within a cell? The answer to this question lies in the process known as DNA packaging , which is the phenomenon of fitting DNA into dense compact forms Figure 7.
During DNA packaging, long pieces of double-stranded DNA are tightly looped, coiled, and folded so that they fit easily within the cell.
Eukaryotes accomplish this feat by wrapping their DNA around special proteins called histones , thereby compacting it enough to fit inside the nucleus Figure 8. Together, eukaryotic DNA and the histone proteins that hold it together in a coiled form is called chromatin. It is impossible for researchers to see double-stranded DNA with the naked eye — unless, that is, they have a large amount of it.
Modern laboratory techniques allow scientists to extract DNA from tissue samples, thereby pooling together miniscule amounts of DNA from thousands of individual cells.
When this DNA is collected and purified, the result is a whitish, sticky substance that is somewhat translucent. To actually visualize the double-helical structure of DNA, researchers require special imaging technology, such as the X-ray diffraction used by Rosalind Franklin. However, it is possible to see chromosomes with a standard light microscope, as long as the chromosomes are in their most condensed form.
To see chromosomes in this way, scientists must first use a chemical process that attaches the chromosomes to a glass slide and stains or "paints" them.
Staining makes the chromosomes easier to see under the microscope. In addition, the banding patterns that appear on individual chromosomes as a result of the staining process are unique to each pair of chromosomes, so they allow researchers to distinguish different chromosomes from one another. Then, after a scientist has visualized all of the chromosomes within a cell and captured images of them, he or she can arrange these images to make a composite picture called a karyotype Figure This page appears in the following eBook.
Aa Aa Aa. What components make up DNA? Figure 1: A single nucleotide contains a nitrogenous base red , a deoxyribose sugar molecule gray , and a phosphate group attached to the 5' side of the sugar indicated by light gray.
Opposite to the 5' side of the sugar molecule is the 3' side dark gray , which has a free hydroxyl group attached not shown. Figure 2: The four nitrogenous bases that compose DNA nucleotides are shown in bright colors: adenine A, green , thymine T, red , cytosine C, orange , and guanine G, blue. Although nucleotides derive their names from the nitrogenous bases they contain, they owe much of their structure and bonding capabilities to their deoxyribose molecule.
The central portion of this molecule contains five carbon atoms arranged in the shape of a ring, and each carbon in the ring is referred to by a number followed by the prime symbol '. Of these carbons, the 5' carbon atom is particularly notable, because it is the site at which the phosphate group is attached to the nucleotide.
Appropriately, the area surrounding this carbon atom is known as the 5' end of the nucleotide. Opposite the 5' carbon, on the other side of the deoxyribose ring, is the 3' carbon, which is not attached to a phosphate group. It acknowledges that people have studied DNA in hydrophilic environments forever. But the explanation for helix stabilization was also based on a hydrophilic property — hydrogen bonding. When you place it in a variety of hydrophobic environments, this idea unravels in ways not previously observed.
The news is a oversell of the paper. The PNAS paper only showed hydrophobic stacking helps hold the structure together, instead of undermining the contribution from DNA base pairs. Would be nice to see a XRD data but oh well. Really interesting! Hopefully this allows for further expansion into biology and epigenetics! Not sure how this is news. What does it say repeatedly? That hydrogen bonds bind the two strands.
Yes you are correct …. If they are hydrophilic the situation is different… Some of the components get dissolved in water…. This is not at all what the article says. The idea that hydrophobic forces hold the helix together while the hydrogen bonds provide the sequence specificity is very old; this study does not add to that.
Instead, this study proposes that protein enzymes that work on DNA may take advantage of the hydrophobic effect to function. Not news and very misleading title. Also, not doing justice to the excellent scientists involved. Reflecting contemporary trends, where journalists must sensationalize everything and, ironically, moving away from the truth by doing so. Journalists should take a course in reporting on science and technology.
Then it can find its way to media culture. To report on science to report honestly, the truly new things in contrast to the old and current, on what it has to offer rather than highlight old information and fail or be ignorant to mention that, to get views for their article. Humanity is and should be willing to be informed of genuine knowledge and deserve media that serves to inform rather than serve their own interests.
If journalists look at movies and events so meticulously like lawyers, historians and filmmakers despite experience or being as informed, they should look at science as closely as they can, with respect to their knowledge, to give a condensed representative picture, easily in just as simple however so and as much words. The media has the ear and trust of the public and the opportunity to educate them.
A bonds to T and U and G to C because those are the only partners they can H bond, the only way nucleotides can find and bond to each other, and the collective strand is kept together by hydrophobic forces.
I am more than pleased to see how scientists maintain scientific integrity and adamantly go after misleading and misguided reports of scientific works. I believe in science and the comments I have read here justify that belief. Thank you all.
I know that water is the key to life in all areas. Blood is to be studied more than ever. The life is in the blood. Keep mocking God, for you have no gifts of our Lord. Bible thumpers you make fun of, but I know for a fact that you have no idea how your soul was created and you cannot explain why us humans have dreams or why we dream in our sleep.
Answer that if you dare. God created us all, we each are different in so many ways, yet so much alike in others, therefore what works for some, will not be an overall cure for others. I believe this technology has been advancing very rapidly.
Hence, I believe Partially Enslaved people can be wirelessly switched ever since to More than Partially Enslaved, or to Fully Enslaved for No Apparent Reason at any time of their lives whenever the possible Undercover People may choose to do so. Such as people possibly Committing Suicide. Additionally, I believe if people who may have possible Undercover Implants inside their bodies, express a Complaint or Agree with an expressed Complaint about possible public figures or possible important organizations, these people may possibly contract Cancer or any other possible Serious Disease.
I also believe that numerous important people in the World in any possible career know about the possible Undercover Implants but, also because of their own possible interests, they keep them Undercover. I believe lot of people who possibly know about the Undercover Implants are very good pretenders and actors, and they can be very convincing in their act.
Additionally, I believe that the overwhelming majority of the population of Earth do not know about the possible Undercover Implants. I also believe that not only Humans but animals may be similarly vaccinated with possible Undercover Implants as well.
Hence, I believe animals can be possibly wirelessly manipulated via satellites against Humans whenever I believe the possible Undercover people may choose to do so. Please be aware that these people may want to keep the Human Race Oppressed and Controlled Undercover.
I was an atheist until 3 years ago. God revealed himself to me through supernatural events. I even had a demonic spirit go inside of me. God is very real. You believe in an extremely intelligently designed universe that accidentally created itself. Atheism is absolutely ridiculous. There is not one transitional fossil to support macro evolution.
You believe an intelligently designed world created itself from nothing, you are the NutJob. And when you die, you will go before God Almighty, and you will bow and confess that Jesus Christ is Lord!
That you can bet. No scientist is claiming that God does not exist. Just that it is not the one in your delusion, Jesus Christ or his father. The true god does not make anyone bow — they love you the way you love them. Terrible article. As point out by others the headline is not correct, and DNA being held together by the hydrophobic effect has been known for decades. Try reading the paper first or even better running the article past the authors for feedback before publication.
Lawrence C. Brody, Ph. Featured Content. Introduction to Genomics. Polygenic Risk Scores.
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