AR EN AY (RNA!)

Tavishi

RNA, or ribonucleic acid, is a single-stranded nucleic acid composed of nucleotides. Each RNA nucleotide contains a sugar (ribose), a nitrogenous base, and a phosphate group. Between DNA and RNA, two differences are found.

First, the sugar in DNA, deoxyribose, has one less hydroxyl group than ribose.

bonus points if you know what textbook this diagram is from!!

Second, the pyrimidine base thymine in DNA is replaced, instead, with uracil. Pyrimidine nucleotide bases have one ring, whereas purine bases have two. As a result, pyrimidines and purines bind to each other.

This diagram above is a DNA molecule, but the same principles apply!

RNA is, on paper, meant to be a molecule that serves as a template for protein synthesis. RNA, of course, decided to wear far, far too many hats.

mRNA, or messenger RNA, is the RNA that encodes proteins. During the process of translation, mRNA is "read" by a ribosome to produce a growing chain of amino acids which are components of a protein. Each pair of three nucleotide bases in the mRNA molecule forms a codon, each of which codes for an amino acid (ex. UAU is translated to tyrosine!)

tRNA, or transfer RNA, brings amino acids to the aforementioned growing polypeptide chain by binding to the codon with an anticodon. tRNA has four loops on the opposite side to which the amino acid binds. Directly opposite is the loop with the anticodon. The three other loops are the T loop, variable loop, and D loop, signified by the modified bases present (ribothymidine, inosine, etc.)

rRNA is the primary component of the ribosome. Pretty much said and done.

Moving on to the cool RNAs...

miRNA, or microRNA, is yet another noncoding RNA. miRNA, however, has a role in affecting genetic expression. (the mi actually stands for mischief.) Argonaute proteins are miRNAs' partners in crime- together with a lot of other proteins, create the RNA induced silencing complex (RISC). RISC carries miRNAs to bind to specific mRNAs. After binding, Argonaute proteins grab the mRNA, and slit its throat (...cut out certain sections and use exonucleases). It's all a rather dramatic and violent affair. (God, I love biochemistry.) In the end, the death of one or two mRNAs is worth it if miRNA gets what it wants.

Next, siRNA, or small interfering RNA. If you thought miRNA was cutthroat, siRNA is even worse. siRNA also forms the RISC with Argonaute proteins, but siRNA is cleaved from an mRNA transcript using the Dicer protein.

While siRNA is an exogenous and double stranded molecule, miRNA is endogenous (originates within that cell) and single stranded. Both silence genes via degradation of mRNA.