An Attempt To Unravel Enigma Of Evolution

An attempt to unravel enigma of evolution Exceedingly interesting is a comparison of the structure of one and same the same protein in various organisms . To our amazement , for instance , there is only a slight difference in the sequence of amino acids in the hemoglobin molecules of humans , the horse , the bull and the mosquito . Insignificant variation in the sequence of amino acids of important proteins attended the evolution of living organism fro the lower to higher forms . The course of evolution can be faithfully traced by studying the molecular structures of proteins of various animals . Another important protein - insulin , human insulin is different from that of a pig by one amino acid and from that of a cow by three. Insignificant deviation from normal structure of important proteins also results in serious diseases . for instance , in sickle cell anemia , a serious hereditary illness , the hemoglobin is anomalous: only one amino acid is replaced by another in the complex chain of this blood protein . ( At present , over 100 human mutant hemoglobins are known to exists ) The amino acid sequence in the polypeptide chain(s) of protein is called the primary structure . ( Today , primary structures are known for many hundreds of proteins ) The primary structure of a protein is a kind of text written by means of a 20 letter alphabet ( Since , all proteins are built up of 20 types of amino-acid residue .) The protein text reflects the biological evolution . The comparison of homologous proteins , which perform the same functions in different species allows one to disclose the difference in the primary protein structure . These differences determined by the mutational amino-acid replacement are greater , the farther apart are the biological species . Especially thoroughly studied in this respect is cytochrome-c , the protein of the respiratory chain which is universal to all living organisms . comparison of the primary structure of cytochrome-c of different kinds of permits one to construct the evolution tree . Cytochrome-c is an obligatory participant in the respiration processes of all living organisms , from yeast cells to human beings . Sr. no . 1

Class - Mammalia Man

0.0

Sr. no . 7

Phylum - Chordata Class Sr. Class – Aves and -Mammalia No Reptilia . Whale 1 Penguin 0.00

2 3

Rhesus monkey Donkey

4

Horse

5

Pig

6

Rabbit

0 0.10 0.34 0.43 0.58 0.66

8 9

Kangaro o Dog

10

Elephant

11

Bat

0.88 0.88 1.06 1.22 1.25

2

Hen

- 0.05

3

Duck

- 0.30

4

Emu

- 0.30

5

Dove

- 0.30

6

Tortoise

- 0.80

Note - values of amino acid residues in proteins ( which characterize their degree of irreplaceability ) is used to calculate the differences of the overall values of cytochrome-c of a number of organisms . On the basis of these data , we may infer that the value of the protein chain increases during phylogenesis .Of course , we must not think that the comparison of cytochrome-c can reflect the greater perfection of human brain as compared with brains of an animal . The greater value means that the man has travelled a longer path of evolution . Nucleic acids , and in the first place DNA, are material carriers of hereditary information and define the species specificity of an organism , which has developed in the course of evolution . Ample information on the relationship between organisms has been provided by the DNA molecular hybridization method . Compositionally , the DNA in humans differ by a mere 2-3 % from DNA of chimpanzee , a slightly higher difference is observed for gorilla , more than 10 % difference for the other monkeys , and nearly 100 % difference for bacteria . The study of specific features of the DNA nucleotide composition for various organisms has enabled a passage from the systematics by outward characters to the genetic systematics . This branch of research in the molecular biology is known now as genosystematics . A composition of the DNA nucleotide composition for various organisms has led to rather intriguing conclusions . The DNA specificity ratio, ( G + C) / ( A + T ) , varies within the wide range in microorganisms , while being essentially invariable in higher plants and animals . If ( A + T ) > ( G + C) , the DNA is said to belong to AT-type : ( G + C) > ( A + T ) , the DNA is of GC type . ( A - The amount of adenine , T - The amount of thymine , G The amount of guanine , T - The amount of cytosine ) Variability variations in microorganisms are observed from the extreme GC – type to a distinctly pronounced AT- type . For DNA of higher organisms , the AT – type is persistently retained . One might have conceived an idea that the DNA specificity is lost in higher organisms . As a point of fact , DNA in higher

organisms is as much specific as is DNA in bacteria , but its specificity is primarily determined by the alternating sequences of nucleotides along the chain rather than by the variation in nucleotide composition. Starting from the DNA nucleotide composition , some scientists have come to quite interesting conclusions concerning the origin of multicellular animals and higher plants . DNA of ATtype of these is close to the DNA of fungi , which allows one to presume a common ancestor ( primitive fungaceous organisms ) for animal and fungi .