Answer to Question #120839 in Evolution for NIBEDITA RUDRA

Question

Write a short note on molecular evolution.

Answer 1

According Oxford Dictionary of Science “molecular evolution” – the evolution of DNA, RNA, and proteins over time, with changes in the nucleotides in the case of DNA and RNA and changes in amino acids in the case of proteins. These changes usually occur at a steady rate over time. This means that molecular evolution can be used as a molecular “clock” to date when different species diverged from their last common ancestor.

The chemical theory of the origin of life was put forward by the Russian biochemist Alexander Oparin in the 1920s. Miller’s experiment mimics the formation of organic molecules in the primeval atmosphere.

Random proteinoids show some slow and simple enzyme activities. Primeval synthesis can generate strands of RNA around 50 nucleotides long but with both 2’–5’ and 3’–5’ linkages. Ribozymes are enzymes made of RNA rather than protein. Although few in number they do exist in modern living cells. The RNA World scenario proposes that the first cells had both genes and enzymes made of RNA.

The sequences of DNA and its encoded proteins will gradually change over long periods of time due to the accumulation of mutations. The amino acid sequences of different proteins evolve at very different rates. Duplication is a major mechanism for creating new genes. New genes may also be created by mixing and shuffling segments of pre-existing genes. The ancestries and relationships of groups of organisms may be derived by comparison of DNA sequences. Slowly-changing sequences, such as ribosomal RNA, are needed to compare distantly-related organisms. Rapidly-changing sequences, such as mitochondrial DNA, are used to compare closely-related organisms. Mitochondrial DNA analysis implies that modern humans originated in Africa about 100,000 years ago. DNA may be extracted from dead or extinct organisms and used to reveal their relationships. Horizontal (or lateral) gene transfer occurs when genetic information is passed “sideways” to a relatively unrelated organism (as opposed to a direct descendent). The extent of horizontal gene transfer is difficult to measure accurately and has often been overestimated.