Description of the Science Behind Cloning

Therapeutic and reproductive cloning, as you would imagine, are based on the science of genetics.  One of the foundations of this science is that long molecules of deoxyribonucleic acid called chromosomes contain the instructions for all our biological processes1.  DNA has a sugar-phosphate backbone with bases inside.  There are four kinds of bases, and their arrangement determines our genetic code.  During transcription, the DNA double helix divides, and catalysts push RNA between4.  The catalysts construct codons of information in the RNA.  As the DNA reunites, this “messenger RNA” leaves the nucleus through translation.  A new type of RNA, tRNA (“translator RNA”), then reads the sequences of information and creates the requested series of amino acids.  These amino acids are responsible for our metabolism.

Cloning is founded upon another one of the fundamental genetic procedures: mitosis3.  An organism begins as one cell which contains all the genetic material necessary for life, but through mitosis, it replicates itself millions of times so it can grow to adult size.  First, each of the 46 chromosomes replicates itself into two chromatids (prophase), and the pairs line up along the center of the cell (metaphase).  When the cell pulls apart, the sets of chromatids divide with them, so each of the 2 new cells has a complete set of information (anaphase).  Finally, the cells create nuclei to house their DNA (telephase).

Because each cell has complete genetic information, each cell can create appropriate amino acids through mRNA.  Because each cell divides through mitosis, a manmade cell (a skin cell, for instance) in the right environment can grow into a full organism, as well.  (An electrical pulse is necessary to push non-sperm cells inside eggs.)  The organism which scientists usually harvest for cells is called a blastocyst2.  It is a cluster of a couple dozen pluripotent cells which will eventually become an organism.

Another important process is cell differentiation2.  As the number of cells within an organism grows, they can devote themselves to specific tasks.  Specialized cells synthesize specific parts of the genetic code in order to produce different proteins from their counterparts.  There are over 200 different types of cells, including blood cells, muscle cells, bone cells, and such.  These specialized cells are necessary for biological processes, but because they are committed to specific sets of RNA and proteins, they do not have the same versatility (or “pluripotency”) and fertility as the first cells, which are called stem cells.  Stem cells also have large amounts of telomerase, which helps them reproduce healthy cells more frequently.  Simply put, they are the catalysts for the body’s growth and regeneration3.  Adults still have millions of stem cells for each process.

1. Hill, Allison.  “DNA is the stuff of genes and genomes.”  Presentation made 2006 January 19 in Biology 48 class at Duke University.  <;.  Powerpoint accessed 4 April 2007.

2. Hill, Allison.  “Cloning: therapeutic versus reproductive.”  Presentation made 2006 February 23 in Biology 48 class at Duke University.  <;.  Powerpoint accessed 4 April 2007.

3. Hill, Allison.  “Mitosis and Meiosis.”  Presentation made 2006 February 21 in Biology 48 class at Duke University.  <;.  Powerpoint accessed 4 April 2007.

4. Hill, Allison.  “Transcription, Splicing, Genetic Code, and Translation.”  Presentation made 2006 February 9 in Biology 48 class at Duke University.  <;.  Powerpoint accessed 4 April 2007.

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