Some DNA Basics

This entry is part 1 of 2 in the series "DNA" --

WARNING: Science Content

As with all my posts, I try to include some thought provoking science, as well as interesting water cooler talk.  Good luck.

Deoxyribonucleic acid (DNA)

12 Base Pairs of DNA. For those of you not familiar with chemistry, but think you know what an atom is, each stick in this figure represents a bond between atoms. The color of the stick represents the atom that is being bonded to. If the stick line changes from one color to a different color, then you are bonding two different types of atoms together. (i.e. Grey to White = Carbon bonded to Hydrogen) You’ll also notice that some atoms bond to multiple things and others not so many. How many things it attaches to is determined by where it is on the periodic table of the elements. (Don’t worry about this, just appreciate that different atoms bond to different numbers of other atoms.)

There Is a Lot of It.

As we have mentioned before in a different post, there are about 3 billion base pairs of DNA over 46 chromosomes (23 pairs).  This count is for each cell in your body. You have about 70 trillion cells in your body. Yes, that is 70,000,000,000,000 copies of your complete DNA. (For those of you heady in math, that is 210,000,000,000,000,000,000,000 base pairs in your body right now.)

DNA Is a Storage System

DNA is an elegant storage system, and every time that I stop and think about what it is, I marvel at its simple, yet complex nature. The rotating picture to the right is 12 base pairs. The two separate helices are the attachment points of each side of the base, and the base pairs are the flat planes of atoms that connect one helix to the other. (Go ahead and take a moment and convince yourself that there are only 12 base pairs here. I know that you want to!)

The base pair that is in the center is not “technically” bonded. They are held together with a much weaker force than the standard covalent bond.  They are held together with “hydrogen bonding“.  Hydrogen bonding is an electrostatic force that only exists when hydrogen is bonded to a Flourine, Oxygen, or Nitrogen atom.  When hydrogen is taking part in hydrogen bonding, it acts like a strong magnet would if it were fastened to one piece of metal, and another piece of metal got close to it. DNA would be useless without this weak interaction.  It needs to be able to separate easily.  If it were covalently bonded across the base pairs, it would be useless.  (If you look closely at the rotating DNA picture, you will notice that the base pairs are shown with a break between them. The hydrogen bond between them is just strong enough for the base pairs to line up to one another.)


A closer look at base pairs

A Closer Look at the base pairs (Thanks to Zephyris on Wikipedia). Each of the four base pairs have names, but to keep it simple, they are abbreviated with the letters A,T,C, and G.  —“A” hydrogen bonds to “T”  — “C” hydrogen bonds to “G” — Also notice that the hydrogen bond between the base pairs is represented by a dashed line. (i.e. Not quite as strong as a regular old covalent bond)


DNA Must Break Apart

As a storage system, DNA must continually break apart in order to be read or to be duplicated.  When it is in its double helix form, it is pretty. It is in storage. It just sits there. Hydrogen bonding (which is not nearly as strong as a regular bond) can break apart easily. It can be put together easily. There are two main events that occur with DNA. Copying the DNA strand, and reading the DNA in order to produce the biological machines in the human body that are comprised of proteins.

The following videos describes how the DNA is broken apart and either copied or transcribed.

The Focus of Many Chemotherapy Agents

The main Chemotherapy drugs that are used (at least for Neuroblastoma) focus on the interruption of the copying process. An interruption of the copying process triggers the oncogenes in the cell to cause apoptosis (cell death). While healthy cells have the means and time to do their best job at repairing the cell before sounding the apoptosis alarm, cancer cells are not nearly as patient. When they discover that there is a problem with DNA replication, they will often give up… At least until they assimilate the knowledge of how to repair the DNA or the knowledge of how to keep the chemotherapy drugs out of their cell walls. This adaptation leads to the demise of the effectiveness of chemotherapy drugs in their fight against cancer.