The tangent plane at the point x=a, y=b is the plane that contains all the tangent vectors (at the point) of curves on the surface that pass through the point (a,b,f(a,b)). Another way to define it is to say that this is the plane through the point (a,b,f(a,b)) which is perpendicular to the NORMAL to the surface at that point. The NORMAL to the surface at a point is just defined as the direction perpendicular to all tangent vectors to the surface at that point. Therefore all we need to do to find the equation of the tangent plane is to find a normal to the surface at that point.
Apart from adenine (A), cytosine (C), guanine (G), thymine (T) and uracil (U), DNA and RNA also contain bases that have been modified after the nucleic acid chain has been formed. In DNA, the most common modified base is 5-methylcytosine (m 5 C). In RNA, there are many modified bases, including those contained in the nucleosides pseudouridine (Ï), dihydrouridine (D), inosine (I), and 7-methylguanosine (m 7 G).
A set of five nitrogenous bases is used in the construction of nucleotides, which in turn build up the nucleic acids like DNA and RNA. These bases are crucially important because the sequencing of them in DNA and RNA is the way information is stored. The letters which form the codons in the genetic code are the A C U G of the bases. The larger bases adenine and guanine are purines which differ in the kinds of atoms that are attached to their double ring. The other bases cytosine, uracil, and thymine are pyrimidines which differ in the atoms attached to their single ring. To make nucleotides, these bases attach to a pentose sugar, either ribose or deoxyribose, along with a phosphate group.