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Genetic Structure

Important research tools now exist to better understand DNA structure, gene function and the analysis of genetic interactions - such as how one gene tells another gene what to do.

It has long been recognized that cancer is the result of a cascade of genetic mutations that allow uncontrolled cell growth. Thus, to understand cancer research, it is necessary to become familiar with some very basic components of genetics.

The Five Basic Players

  1. Deoxyribonucleic acid (DNA)

  2. Genes

  3. Chromosomes

  4. Ribonucleic acid (RNA)

  5. Proteins

 

Deoxyribonucleic acid (DNA)

Lets start at the beginning. DNA is the building block of all information needed to form a living thing such as single cell organisms like bacteria, yeast and some viruses or multicellular organisms like humans, trees and starfish.

If you were to lay out, end to end, all the DNA from just one of your cells, the line would be over six feet long. You have roughly 100 trillion cells, so laid out all together the DNA in your body would easily stretch to the sun and back - nearly 100 times!

You're probably wondering how a huge DNA molecule can fit into a very tiny cell so small that you can't see it with the naked eye. Here's how: DNA is tightly packed much like a phone cord thats been twisted around and around itself. So, over six feet of DNA is compressed into only a few thousands of an inch.

DNA is a remarkably durable molecule, it can be stored in ice or in a fossilized bone for thousands of years. DNA can stay in one piece for as long as 100,000 years under the right conditions. This durability is why scientists can recover DNA from 14,000 year old mammoths.
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But What Does It Do?

DNA gives information to a cell directing it to grow, divide, or perform any other function. The main role of DNA molecules is the long-term storage of information.

DNA is often compared to a set of blueprints, a recipe, or a code. It is made up of 4 different bases (chemical molecules) that are attached to a backbone made of deoxyribose sugar and phosphate.

What Does It Look Like?

DNA resides in the “center of the cell” in the nucleus.

   
  DNA only contains four bases:

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

These four bases always pair
as follows:

A always pairs with T

C always pairs with G

These four bases can be arranged and rearranged in countless ways.
Image from The Genetics Home Reference, NIM, NIH    
http://ghr.nlm.nih.gov/handbook

The order in which the four bases pair up ( A-T or T-A; C-G or G-C) and line up next to each other (for example: A-T, C-G, G-C) determines the message to be conveyed, much as specific letters of the alphabet combine to form words then sentences. These base pairs line up in groups of three called codons. These three base pairs are known as amino acids and they are the building blocks of proteins.

 

More specifically, in all living organisms each collection of three DNA base pairs forms a "word". Collections of many "words" formed from the three DNA base pairs then form a sentence or "gene".

For example, any combination of the four bases ( A-T or T-A or C-G or G-C) can come together to form 3 base pairs and are then called an amino acid. These amino acids then come together to form proteins.
Image courtesy of Genome Management Information System,
Oak Ridge National Laboratory

What Is DNA Replication:

For a cell to divide, it must first make a copy of itself or replicate its DNA. Scientists use the term "double helix" to describe DNA's structure where two complementary strands of DNA wind around itself.

This shape, which looks much like a twisted ladder, gives DNA the power to pass along biological instructions with great precision.

The two strands are connected to each other by chemical pairing of each base on one strand to a specific partner on the other strand.

 

When DNA is copied, the two strands of the old DNA are pulled apart or separated by enzymes.

The separated single strands serve as templates for building two new, double-stranded DNA molecules, each a replica of the original DNA molecule.

This produces two new copies of DNA, each containing one strand from the old DNA and one newly made strand.
Image courtesy of Genome Management Information System,
Oak Ridge National Laboratory

In addition, when proteins are being made, the double helix unwinds to allow a single strand of DNA to serve as a template. This template strand is then transcribed into mRNA, which is a molecule that conveys vital instructions to the cell's protein-making machinery.

Despite its complexity, replication is unbelievably fast. In humans, replication speeds along at about 2,000 bases a minute, so, it's really no surprise that sometimes mistakes are made. In fact, about 1 in every 100,000 bases is incorrect.
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