(Image credit: Universal History Archive/Universal Images Group via Getty Images) (opens in new tab)ĭNA was first observed by Swiss biochemist Friedrich Miescher in 1869, according to a paper published in 2005 in the journal Developmental Biology (opens in new tab).
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 (opens in new tab). 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 (opens in new tab). 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 (opens in new tab)" (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.
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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.
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