Biology, Vol. 4 (Pr-Z) by Richard Robinson

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By Richard Robinson

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Euglena are most common in organically rich freshwater environments. 24 unicellular algae. Modern taxonomic treatments recognize these similarities and group protozoa, photosynthetic unicellular algae, and slime molds together as protists or protoctists. Whichever term one prefers, the classification is not monophyletic. Despite the fact that protozoa is not a proper taxonomic name, it is a useful, functional term. Ecologists differentiate between autotrophic and heterotrophic components of an ecosystem, and it is natural to separate the animal-like protozoa from the photosynthetic algae based on their nutritional mode.

An example of such a targeting sequence is the so-called nuclear localization signal (NLS), which consists of two short stretches of basic amino acids divided by a 10–11 amino acid spacer region. This sequence of amino acids allows a protein possessing it to bind to nuclear localization receptors found in the nucleus. Once a protein containing an NLS signal binds to a nuclear receptor it is no longer able to freely diffuse and becomes “localized” to the nucleus. Many proteins are embedded within or associated with membranes.

The A site is now empty of tRNAs and the next aminoacyl tRNA can be brought into it. Many antibiotics (drugs that kill bacteria) affect the elongation phase of prokaryotic translation. Some decrease the fidelity (accuracy) with which the ribosome decodes the mRNA and the wrong amino acids get put into the proteins. This decrease in fidelity leads to an accumulation of proteins that do not work, which eventually kills the bacterium. Other antibiotics prevent the formation of the peptide bond or the movement of the tRNAs by EF-G after the peptide bond has been formed.

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