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From Molecules to the First Cell
The prebiotic conditions on the earth in all probability were volcanic eruptions, lightning and heavy rains. There was no trace of free oxygen or an ozone layer in the atmosphere to absorb ultraviolet radiations from the sun. It is assumed that organic molecules would have originated in such climatic conditions. This is described as their abiotic origin. Laboratory experiments from 1953 onwards prove that organic molecules like amino acids, proteins, nucleotides, nucleic acids, lipids and ATP can be formed in similar conditions on the earth. Stan1r.y Miller's experiment described below is one such experiment (Fig. shown below). It is possible that such organic molecules similar to those synthesised in Miller's experiment would have got accumulated at several places in high concentration, giving rise to a kind of liquid soup.
Scientists have three different speculatiohs about the composition of a protobiont. Some consider it'as an aggregate of electrically charged molecules with water around them acting as a boundary and this is called as coacervate model (Fig. shown below). This model was proposed by Alexander Oparin. Sidney Fox proposed another model for protobiont formation called protenoid microsphere model. According to this model when water free mixtures of amino acids are heated at high temperature, they pol.yinerise to form protein-like molecules, called proteinoids. These can persist only if cooled quickly. According to a third model called as the lipid bilayer model of Richard Goldacre, an abiotically synthesised phospholipid bilayer was formed around a central space containing organic molecules. All such models are without any experimental or theoretical evidence. However, the supporters of each model try to explain how some life-processes like osmosis and budding, can be camed out by such protobionts.
ERRORS IN FERTILIZATION - 1. Polyspermy - When more than one sperms are fused in an ovum, this condition is called polyspermy. 2. Polygynae - During oogen
Define the Food and Nutrition Security? In the previous section, we learnt about the trends in production of food grains in the country and their relationship to population gro
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CARBOHYDR A TES Carbohydrate = hydrate of carbon. Hydroxyl group present. Aldehyde group or keto group may present. Carbohydrates are polyhydroxy aldehydes
nucleolus is formed by
Single chromosome of a pair is known as homologue.In Homologous pair two identical chromosomes are there. Each one chromosome in a Homologous pair is known as Homologue.
Artificial Inspiration : a. After artificial expiration, the rescue worker should slowly release the pressure on the back of the victim. b. This will cause the chest cavity t
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In a chemical reaction the free energy change (/\Go') is -40 jk/mol and the entropy factor T/\S is 15 kj/mol. the enthalpy change /\H for the reaction is a. 25 kj/mol b.-25 k
How is the chromosome region where the centromere is located called? How are chromosomes classified in relation to the position of their centromere? The chromosome region where
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