Attenuation is the regulatory mechanism to control gene
expression or transcription. Attenuation
was first observed in trp operon of E.Coli bacteria (commonly found at
guts of warm blooded animal). E.Coli
bacteria need tryptophan which is a kind of amino acid. The bacteria can either
take tryptophan from environment or itself synthesize by using bio synthetic
enzymes. These bio synthetic enzymes are encoded by five genes located next to
each other which we called as trp operon.
When tryptophan levels are high, then the transcription of trp
operon is controlled. This process is called Attenuation. In this process
the RNA polymerase is prematurely stopped during transcription of trp operon
which results in formation of short mRNA. Due to premature control such mRNA
doesn’t gets encoded with tryptophan biosynthesis enzymes.
Attenuation is carried out when tryptophan level is high, so
as to prevent unnecessary production of biosynthetic enzymes which are needed
to make tryptophan.
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Nitrogen Fixation. It's the process by which atmospheric nitrogen is converted either by a natural or an industrial means to form of nitrogen such as ammonia.
Answer:
Homologous characters indicate descent through modification from a common ancestor.
Explanation:
Homologous characters have the same fundamental structures. They also share the same relations with adjacent structures, and they have the same embryological development.
These structures might show variations between organisms exhibiting them, according to their function and to the environment in which the organism lives.
These homologous characters are common in organisms related and that share a <u>common ancestor</u>.
For example, whales, humans, and horses all have the same bones in the same order, but they matured differently in later embryological development. This is an example of homologous characters.
