Where it all begins - DNA

DNA, known to biochemistry geeks and molecular biologists as Deoxyribonucleic acid. 

DNA Stores Information

This is the information center of the cell. It contains instructions for the cell that describe how to reproduce, how to communicate, how to maintain itself, how to eat, how to sleep—put simply, what the inputs and outputs of the cell should be.  The DNA performs the same function in a cell that blueprints,  and managers play in  a factory. Blueprints determine how the machinery is put together, and managers  decide which machines and hardware to keep in the factory. DNA provides both functions by determining which proteins are created, and how those proteins are structured. 

How Does DNA Store Info? A New Alphabet

DNA is actually a long string of smaller molecules arranged in a pattern. The pattern is what determines the instructions contained in the DNA, in the same way that this sentence is a string of letters, and the particular order of the letters is what determines the meaning. The alphabet used to create DNA sentences contains only four letters: A,T,G, and C. The letters stand for Adenine, Thymine, Guanine and Cytosine. But the possible number of sentences is unlimited, as attested by the variety of life on earth. 

 Double-Helix

That famous "double helix" shape that you always see in illustrations and logos comes from the physical structure that DNA takes. In nature, you rarely see a single strand of DNA floating around by itself. Most commonly, DNA is found as a double-stranded molecule. One strand contains the genetic instructions for the cell, and the other strand contains the "anti-instructions". Besides being beautiful and providing a high-tech aura to company logos, the double helix structure provides stability to the molecule and is part of the reason why DNA is used for cellular information storage. The reason the double helix forms  is simple—each letter in the genetic code (from now on I'll refer to them as "bases") pairs with one of the other bases. A pairs with T and C pairs with G. Two strands of DNA with complementary sequences will come together just like a zipper. Suppose you had the sequence AGTCC, then the complementary strand would be:

ATGCCATGA DNA

||||||||| ---

TACGGTACT DNA

Discovery of the 3D structure of DNA is attributed to James Watson and Francis Crick. Remember their names if you hope to be a biotech nerd someday. You may hear the term "Watson-Crick base pairing", and now you know that it refers to strings of bases  bonding to each other to form that pretty helix structure. When referring to the genome size of an organism, we are talking about how much DNA is contained in a cell, and that number is usually given in base pairs (bps). The sequence above— "ATGCCATGA"— is nine 

bases long (the double-stranded version would be nine bps long). 

In the Lab

Just as an aside, in the lab DNA is usually stored in buffer (water with some salts), and it doesn't look much like the pictures you see in Discover magazine. It just looks like water. However, under a scanning electron microscope, you can see DNA inside cells.

Grammer School

The grammar of the DNA instructions consists of three-base triplets that each correspond to an amino acid. Amino acids are the building blocks of proteins, and proteins are the machinery that perform work in the cell. However, DNA cannot be translated directly to protein. First, a working copy of the genetic instructions is made from RNA.

We will talk about some of the grammar rules when we discuss RNA and Proteins. Back to grammar school with you ...