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Nucleic acid structure - why DNA & RNA look that way

DNA and RNA were getting jealous… Amino acids (protein letters) tend to get the most attention structure-wise (at least by me, I’ll admit). But in order for the right amino acids to be added in the right order to give you the right protein, you need to have a really clear recipe. You need to be able to copy those recipes each time a cell divides so you never lose it, and it can’t be like a game of telephone, where the message changes slightly when you pass it down. Instead, these recipes have to be faithfully replicated, and protected between copy-making. So you keep them locked up safe like encyclopedias in the reference section of a library and, when you want to make the protein, you don’t work with the original recipe, instead you “Xerox” it and give the “chefs” (protein-making machinery called the ribosome) copies to work with. How to achieve all of this? NUCLEIC ACIDS!  So, before the year’s over, let’s review! blog form: http://bit.ly/nucleicacids2     “Nucleic acid” is a category that includes RNA (RiboNucleic Acid) and DNA (DeoxyRiboNucleic Acid). The original recipe (the one that is kept in the “reference section”) is written in DNA & the “Xeroxes” are made in RNA. The nucleic acid “alphabet” is made up of “letters” called nucleotides, similarly to how the protein “alphabet” is made up of letters called amino acids - but the nucleic acid alphabet is a lot smaller - just 4 DNA letters & 4 RNA letters - as opposed to the 20 (common) amino acids.     The letters of both alphabets have generic backbones for easy linking (a sugar-phosphate backbone for nucleic acids and a (carboxylic acid-alpha carbon -amino group) for amino acids, but they also have unique parts that give them different properties. For nucleotides, the unique parts are nitrogenous bases and they can form specific base pairs with each other (A to T (or U in RNA)) and C to G. This way you can use one strand of double-stranded DNA as a template for making the other one (which if you used that as a template would give you back the 1st strand…)     For amino acids, the unique parts are the “side chains” or “R groups” which range from small and flexible to large and bulky, negative, positive, or neutral. These different properties help proteins fold up into intricate shapes and carry out various functions. But in order to get those functional proteins you have to make sure you link up the write letters and this is one where DNA comes in.    The instructions for what order to link the amino acids in are written in DNA as genes. Because those instructions are so important, this DNA is kept “locked up” safe and sound in a membrane-bound “room” in your cells called the nucleus. It’s kinda like a “reference section” of a library - you can’t check out books, but you can read them & even make copies. If you need to make a protein, you have to find the recipe for it. Then you have to TRANSCRIBE a copy of it into the related RNA language. Then you can take this MESSENGER RNA (mRNA) copy out of the nucleus & into the CYTOPLASM (general cellular interior) where RIBOSOMES (protein/RNA molecular machines) TRANSLATE the mRNA into the PROTEIN language of AMINO ACIDS.    The combination of ALL the DNA in one of your cells is called your GENOME. You can think of it like a super long cookbook where the recipes for making proteins, functional RNAs, etc. are regions of DNA called GENES. The genome’s split up into “volumes” called CHROMOSOMES & you have 46 of them. 46? Then why’s it called “23 and me?” 23 pairs - you have 2 copies of each volume - 1 you inherited from each of your biological parents.  (Well, at least 22 pairs - the autosomal (non-sex ones), the "sex chromosomes" (X & Y) can be different).   The copies are mostly the same (except for the pair of sex chromosomes which can be different) - they have recipes for making the same things BUT small differences in the recipes (POLYMORPHISMS) lead to slight differences in the final products &/or when they’re made. This variety is good (polymorphisms are the spice of genetic life) because the slightly different versions might be slightly better in certain situations. BUT you might also have “typos” (harmful mutations) in 1 copy of a recipe, but thankfully you have a backup! (🤞 your backup’s ok)  Just like proteins have layers of structure (primary structure’s sequence of amino acids, secondary structure’s things like helices & strands made through backbone-backbone interactions, tertiary involves side chains, & quaternary involves more than one polypeptide chain) nucleic acids have structure too. The sequence of nucleotide “letters” in nucleic acids (DNA & RNA) defines its PRIMARY STRUCTURE & base-pairing between those nucleotides gives it SECONDARY STRUCTURE    And just like with proteins, the primary structure is of primary importance, so let’s take a closer look at these nucleic acid letters!  finished in comments