This week on Sciencism; 60 years since the double helix DNA special feature. Science news; space junk threat, bird navigation – iron balls, cure your lazy eye with tetris, diesel from E.Coli and validating relativity again. Last week in the past, science or fiction and the science quiz.
Space Junk Threat
Bird Navigation – Iron Balls
Cure Your Lazy Eye With Tetris
Diesel From E.Coli
Validating Relativity Again
Last Week In The Past
Science or Fiction
Bacteria Evolve Resistance More Quickly With Stronger Antibiotics
Humans Pass On Drug Resistance to Animals In Protected Africa
- In Some Fish The Colour of Scales Predicts Winners in a Fight Better Than Size
Which mathematical theory describes the strategy involved in decision making and who first offered mathematical proof of this theory?
This Week’s Question
Which organelle found inside living cells “read” mRNA and utilise tRNA to produce primary protein structures? Who won the nobel prize for the discovery of this organelle?
Science Feature – DNA 60th Anniversary
The History of DNA and Inheritance
The idea that traits were inherited in a predictable way began with Gregor Mendel in the 19th century. Mendel cross bred pea plants with different features such as height and flower colour. To his surprise he found that when he crossed a dwarf plant with a tall plant rather than a medium sized plant, a tall plant was produced. When crossing this generation 1 in 4 of the plants produced would be a dwarf plant, this lead him to believe that traits were passed between generations in ‘heritable units’. Mendel’s work remained obscure for some time until it was rediscovered in 1900, it was at this time the search for a vector for these so called ‘heritable units’ began.
DNA – Deoxyribonucleicacid was isolated for the first time in 1869 from the pus of surgical bandages by swiss physician Friedrich Miescher, though at the time little was known about the role of this molecule. By 1919 Albrecht Kossel and Phoebus Levene had contributed knowledge of the 5 bases and phosphate backbone of DNA, but still its role in the inheritence of traits was not known.
In 1927 Nikolai Koltsov proposed the idea that inherited traits would be passed on by a “giant hereditary molecule” that would have “two mirror strands that would replicate in a semi-conservative fashion using each strand as a template”, the exact mechanism by which we now know that DNA encodes the heritable gene essential to life.
After much experimentation trying to identify this giant hereditary molecule it was in 1952 that Alfred Hershey and Martha Chase proved that DNA was the molecule that carried the genetic information of the bacteriophage T2, and thus DNA was confirmed as the molecule that carried an organism’s genetic information.
60 years this week in 1953, James Watson and Francis Crick published their analysis in Nature of the X-ray diffraction picture of the DNA molecule which was produced by Rosalind Franklin and Raymond Gosling. Their analysis confirmed the double helix structure which supported the semi-conserved template hypothesis of Koltsov.
Why DNA works
Everything in your body is coded for by DNA. As Ross mentioned earlier, DNA has two strands of phosphates and sugars which form the backbones. Between the backbones sit the nucleic acids, called guanine (G), cytosine (C), adenine (A), and thymine (T). Guanine only binds with cytosine, and adenine only binds with thymine. The nucleic acids are each attached to sugar and phosphate to make a unit called a nucleotide.
In order for the DNA to be used by the body, it needs to be decoded. This is done via two step process involving transcription to RNA then translation to amino acids which then fold upon themselves to form proteins. A molecule called RNA polymerase attaches to a strand of DNA at the beginning of a section which codes for a particular gene, or the “start” codon. The RNA polymerase moves along the DNA strand and breaks apart the hydrogen bonds between the nucleic acid pairs. This splits the DNA double helix into two single strands. Only one of these single strands is read during the transcription process. RNA nucleotides are matched to the single DNA strand to form a strand of messenger RNA (mRNA). This continues until the polymerase molecule reaches and recognises the combination of nucleic acids that codes for “stop”. The mRNA then holds a copy of that gene’s information. Keep in mind that humans have over 25,000 genes.
mRNA is transported to the part of the cell called the endoplasmic reticulum. The strand is fed through and nucleic acids are recognised in groups of three which then code for an amino acid. As each new group of three nucleic acids is recognised by the endoplasmic reticulum, the corresponding amino acid is attracted to the site and added to the chain of amino acids that has been constructed from previous decoding; This is the primary structure of the protein. These amino acids then interact amongst themselves binding together where there are attractive forces and pushing apart where there are repulsive forces – similar to how magnets work. This gives them their secondary and tertiary structures – taking them from a straight line of linked amino acids, to coils, zig-zags, and sheets, up to complex folded proteins with very specifically shaped and electronically charged sites for interaction with other molecules.
The proteins are then exported from the cell and move out into the rest of the body, usually via the bloodstream, to perform their particular action.