Darwin’s Tea Party. The Biological Revolution: DNA and Modern Genetics Winter 2009. After Mendel . Gregor Mendel (1822-1884) had discovered the basic mechanisms of heredity.
Darwin’s Tea Party
The Biological Revolution: DNA and Modern Genetics
In 1951 James Watson (1928- ) and Francis Crick (1916- ) discovered the structure of the DNA molecule - Deoxyribonucleic Acid
In this famous photograph Watson (right) and Crick (left) demonstrate a model of the DNA molecule.
DNA was soon shown to be the mysterious material particle sought for since Mendel’s discoveries.
DNA exists in the nucleus of almost every cell in the body, beginning from day 1 when you were just an embryo.
Cross section of skin, showing skin cells.
DNA is inside the nucleus of a cell, within its chromosomes
The DNA molecule is structured in a “double helix” shape (like two spiraling staircases).
One helix is connected to another by base pairs – shown here as “A”, “T”, “C”, “G”.
Base pairing rules
The base pairs, though, must connect following the base-pairing rules so that “A” connects only with “T” and “C” with “G”.
A Japanese molecule
A DNA sequence is simply the order of base pairs along the DNA double spiral.
In this case, we note the sequence “T-A” “C-G”
What is a gene?
A gene is thus a segment of DNA containing varying lengths of DNA base pair sequences (T-A, C-G, G-C, T-A, etc…).
Actually, the route from DNA sequence to protein is a bit more complicated. First the DNA sequence spells out a certain type of amino acid and that then helps produce a certain type of protein.
In this example, the genetic disease sickle cell anemia can be traced back to a single genetic “spelling mistake” in the genetic sequences contained in the upper part of chromosome 11:
Genes can control certain traits; as in flower colour in this example.
Of course, we don’t always associate bacteria and viruses with helpful effects!
Here, for example, are two unhelpful bacteria, the Tobacco Mosaic Virus and Human Immunodeficiency Virus (HIV) which produces AIDS.
The T4 bacteriophage is a virus which attack the E. coli bacteria.
Genetic engineering techniques can be used for altering genetic sequences responsible for genetic diseases. This is called gene therapy.
In this case, missing sequences causing Cystic fibrosis can be inserted into the genetic code of a CF patient using a virus as delivery vehicle.
Here the gene for producing insulin is taken from a human chromosome and inserted into a bacteria’s plasmid (a single ringed chromosome). This plasmid with the human insulin gene can then be used to produce insulin to treat certain forms of diabetes.
This is one example of how genetic engineering techniques can be used to create pharmaceuticals or medicines.
But what if we could change the genetic blue print – the genetic sequences that ultimately make up life?
Scientists can alter genes by cutting out undesired and inserting desired sequences. In this case a gene from a bacteria called Bt which acts like an insecticide is being inserted into the genetic code of a corn plant. The corn will thus contain this built in insecticide.
Fears of genetic engineering often go back to the Frankenstein story.
Thus, many applications of genetic technology exist, including: