![]() In that paper, they proposed the iconic double-helix model of DNA as we now know it, with sugar-phosphate sides and rungs made up of A-T and G-C base pairs. Armed with the information that DNA was a double helix and previous reports that the bases adenine and thymine occurred in equal amounts within DNA, as did guanine and cytosine, Watson and Crick published a landmark 1953 paper in the journal Nature. In 1953, Wilkins showed the photo to biologists James Watson and Francis Crick - without Franklin's knowledge. Franklin documented this structure in what became known as Photo 51. In 1952, chemist Rosalind Franklin, who was working in the lab of biophysicist Maurice Wilkins, used X-ray diffraction - a way of determining the structure of a molecule by the way X-rays bounce off it - to learn that DNA had a helical structure. (The term "nucleic acid" derives from "nuclein.")īut for many years, researchers did not realize the importance of this molecule. Miescher used biochemical methods to isolate DNA - which he then called nuclein - from white blood cells and sperm, and determined that it was very different from protein. (Image credit: Universal History Archive/Universal Images Group via Getty Images)ĭNA was first observed by Swiss biochemist Friedrich Miescher in 1869, according to a paper published in 2005 in the journal Developmental Biology. Rosalind Elsie Franklin (1920-1958) was a British chemist and crystallographer who is best known for her role in the discovery of the structure of DNA. But there is some natural variation in the number of sex chromosomes people carry - sometimes, there may be extra sex chromosomes, or one might be missing, so other patterns, such as X, XXX, XXY and XXYY, can also occur, Discover reported. In general, females carry two X sex chromosomes in each body cell and males carry one X and one Y. Most chromosomes look like microscopic Xs that said, humans and most other mammals carry a pair of sex chromosomes that can be either X or Y-shaped, according to the National Human Genome Research Institute. Humans have 23 pairs of chromosomes, which are found inside each cell's nucleus, the control center of the cell. Each chromosome contains a single DNA molecule, wrapped tightly around spool-like proteins called histones, which provide chromosomes their structure. To fit inside cells, DNA is coiled tightly to form structures called chromosomes. Freeman and Company, 2002).ĭNA molecules are long - so long, in fact, that they can't fit into cells without the right packaging. This RNA copy, called messenger RNA (mRNA), tells the cell's protein-making machinery which amino acids to string together into a protein, according to " Biochemistry" (W. Then, an enzyme zooms in and constructs a new RNA molecule whose sequence mirrors that of the unzipped gene. In addition, while RNA has three of the four nitrogen bases in common with DNA, it uses a base called uracil rather than thymine to pair with adenine.Īs a cell prepares to build a new protein, its DNA unzips to expose one strand of the gene with the instructions to build said protein. RNA shares a similar structure to DNA, except it contains only one strand, rather than two - so it looks like just one half of a ladder. To make a protein, the cell makes a copy of the gene, using not DNA but ribonucleic acid, or RNA. The shorthand for this process is that genes "encode" proteins.īut DNA is not the direct template for protein production. Similar to the way that letters in the alphabet can be arranged to form words, the order of nitrogen bases in a DNA sequence forms genes, which, in the language of the cell, tell cells how to make proteins. The scientists detailed their findings online April 26 in the journal Nature Communications.įollow us on Twitter Spacedotcom and on Facebook. In addition, imidazole can act like a primitive catalyst to set off chemical reactions, such as forming purines instead of pyramidines. Imidazole and similar molecules proved far more abundant than pyramidines in these meteorites, suggesting they might prove easier for naturally occurring chemical reactions to synthesize. Oba suggested a clue might lie in the fact that purines include a pentagonal ring known as imidazole, whereas pyramidines do not. ![]() It remains uncertain why pyramidines were so much less abundant in these meteorites than purines. "Due to our findings, we can say nucleobases also show wide varieties in carbonaceous meteorites," Oba said. Scientists find liquid water inside a meteorite, revealing clues about the early solar system Too much of a good thing: Early impacts delivered iron to Earth but almost wiped out life Your RNA may have come from space, meteor study suggests
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