Lecture 2 – Theories of Origin of Life PDF

CSU1879-Biology for Engineers Lecture 2 –Theories of Origin of Life  Topics to be covered today 1.Introduction – cell theory 2. Postulates of different theories – Definitions – Objections – Significance – Exceptions 3. Ho...

CSU1879-Biology for Engineers Lecture 2 –Theories of Origin of Life  Topics to be covered today 1.Introduction – cell theory 2. Postulates of different theories – Definitions – Objections – Significance – Exceptions 3. Homework  Introduction Several attempts have been made from time to time to explain the origin of life on earth. As a result, there are several theories which offer their own explanation on the possible mechanism of origin of life. 1. Big Bang Theory  2. Theory of special creation  The greatest supporter of this theory was Father Suarez. According to this theory life was created by supernatural power. According to the Bible the world was created within six days. On the first day God made the heaven and the earth, on the second day, on the fourth day, He formed the sun, the moon and the stars, on the fifth day, He created the whole universe with his desire.  According to the Hindus the Lord Brahma created the living world in one stroke. The first man was Manu and the first woman was Shradha.  Special creation theory lacks scientific evidences, on account of which it is not accepted.  3. Theory of Panspermia/Cosmozoic Theory  This theory was proposed by Richter (1865).  According to this theory, ‘protoplasm’ reached the earth in the form of spores or germs or other simple particles from some unknown part of the universe with the cosmic dust, and subsequently evolved into various forms of life.  Helmholtz (1884) speculated that ‘protoplasm’ in some form reached the earth with falling meteorites.  Arrhenius (1908, Nobel Prize Winner of 1903 in Chemistry) postulated the (= Panspermia Theory) and stated that organisms existed throughout the universe and their spores etc., could freely travel through space from one star to the others.  In fact, panspermia theory is the alternative name of cosmozoic theory  4. Theory of spontaneous generation  This theory states that life originated from nonliving things in a spontaneous manner. In ancient Egypt, it was believed that the mud of the Nile could give rise to frogs, toads, snakes, mice and even crocodiles when warmed by the sun.  Van Helmont (1577-1644) held that human sweat and wheat grains could give rise to organisms. He placed a dirty shirt in a receptacle containing wheat bran and found that after 21 days the gases from the shirt and wheat had formed living mice.  These beliefs have no scientific grounds and hence are discarded.  Some other different cell theories about origin of life 5. Theory of catastrophisicm:- Georges Cuvier (1769-1832), Father of “Modern Palaeontology” and Orbigney (1802- 1837) were the chief advocates of this theory. According to this theory cataclysms (great destruction) or catastrophic (concerning disastrous event) revolution occurs upon earth from time to time which completely destroys all organisms (living beings).New organisms, then, suddenly form from inorganic matter. Each creation consists of life quite different from that of the previous one. In fact, this theory is merely a modification of theory of special creation. This theory is also not accepted. 6. Theory of Eternity of life: Life only changes its form but is never created. It has no origin and has always existed.  7. Theory of Biochemical evolution Also known as Materialistic Theory or Physico-chemical Theory. Proposed independently by a Russian scientist, A.I. Oparin, in 1923 and an English scientist, J.B.S Haldane, in 1928. According to this theory, Life originated from pre-existing nonliving organic molecules (RNA , Protein etc.) and that formation of life preceded by chemical evolution.  Recent developments.........  In April 2011, researchers in Italy found that if they mixed formamide, a simple chemical present in space, with material from a meteorite, and then heated the mixture, that they produced nucleic acids (building blocks of DNA and RNA), the amino acid glycine, and a precursor to sugar.  In February 2010 scientists at the Scripps Research Institute in San Diego announced that they have synthesized RNA enzymes, known as ribozymes, that can replicate themselves without the help of any proteins or other cellular components.  In May 2009, a team led by John Sutherland, a chemist at the University of Manchester in England discovered how the basic nucleotides (building blocks) of RNA could spontaneously assemble. He formed the RNA nucleotide ribocytidine phosphate from cyano-acetylene. Recent developments.........  Conclusion All the evidence gathered thus far has revealed a great deal about the origin of life, but there is still much to learn. Numerous scenarios have been explored for many years, but there is still a large gap between what is known and what is unknown. Because of the enormous length of time and the tremendous change that has occurred since then, much of the evidence relevant to origins has been lost and we may never know certain details. Nevertheless, many of the gaps in our knowledge (gaps that seemed unbridgeable just 20 years ago) have been filled in recent years, and continuing research and new technologies hold the promise of more insights. Thank you Geetansh School of Bioengineering and Food Technology Shoolini University Village Bhajol, Solan (H.P) 9805985357(Mob No.) [email protected]