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A scenario is a set of related concepts pertinent to the origin of life (abiogenesis), such as the iron-sulfur world.Many alternative abiogenesis scenarios have been proposed by scientists in a variety of fields from the 1950s onwards in an attempt to explain how the complex mechanisms of life could have come into existence.
Pseudo-panspermia (sometimes called soft panspermia, molecular panspermia or quasi-panspermia) is a well-supported hypothesis for a stage in the origin of life.The theory first asserts that many of the small organic molecules used for life originated in space (for example, being incorporated in the solar nebula, from which the planets condensed).
Living organisms use molecules that have the same chirality (handedness): with almost no exceptions, [281] amino acids are left-handed while nucleotides and sugars are right-handed. Chiral molecules can be synthesized, but in the absence of a chiral source or a chiral catalyst, they are formed in a 50/50 (racemic) mixture of both forms.
Endocrinology (from endocrine + -ology) is a branch of biology and medicine dealing with the endocrine system, its diseases, and its specific secretions known as hormones.It is also concerned with the integration of developmental events proliferation, growth, and differentiation, and the psychological or behavioral activities of metabolism, growth and development, tissue function, sleep ...
While differing in details, these hypotheses are based on the framework laid out by Alexander Oparin (in 1924) and John Haldane (in 1929), that the first molecules constituting the earliest cells . . . were synthesized under natural conditions by a slow process of molecular evolution , and these molecules then organized into the first molecular ...
The aromatic/arginine or "ar/R" selectivity filter is a cluster of amino acids that help bind to water molecules and exclude other molecules that may try to enter the pore. It is the mechanism by which the aquaporin is able to selectively bind water molecules and so to allow them through, and to prevent other molecules from entering.
To release active hormones quickly into the circulation, hormone biosynthetic cells may produce and store biologically inactive hormones in the form of pre-or prohormones. These can then be quickly converted into their active hormone form in response to a particular stimulus. [34] Eicosanoids are considered to act as local hormones. They are ...
The hydrophobicity hypothesis states that highly hydrophobic (water hating) proteins (such as the membrane bound proteins involved in redox reactions) are not easily transported through the cytosol and therefore these proteins must be encoded in their respective organelles. The code disparity hypothesis states that the limit on transfer is due ...