The process of RNA editing is the alteration of the sequence of nucleotides in the RNA after it has been transcribed from DNA, but before it is translated into a protein. RNA editing occurs by two distinct mechanisms:<em><u /><u>Substitution</u> <u>editing </u></em>and <u><em>Insertion/</em></u><em></em><u><em>deletion</em></u><em> <u>editing</u></em>.
<u><em>Substitution editing</em></u> is the chemical alteration of individual nucleotides. These alterations are catalyzed by enzymes that recognize a specific target sequence of nucleotides:
*Cytidine Deaminases that convert a C in the RNA to uracil.
*<em />adenosine deaminases that convert an A to inosine,which the ribosome translates as a G.<span>Thus a CAG codon</span><span> (for Gln) can be converted to a CGG codon (for Arg).
<em><u>*Insertion/deletion editing</u></em><em><u /></em><u /> is the insertion or deletion of nucleotides in an RNA.
These alterations are mediated by guide RNA molecules that base-pair as best they can with the RNA to be edited and serve as a template for the addition( or removal) in the target.</span>
Bilirubin is a byproduct of red blood cell destruction and are conjugated in the liver and excreted in bile.
“This transient switch in membrane potential is the action potential. The cycle of depolarization and repolarization is extremely rapid, taking only about 2 milliseconds (0.002 seconds) and thus allows neurons to fire action potentials in rapid bursts, a common feature in neuronal communication.”
It takes about one minute for a blood cell to make a complete circuit of the human body.
A. A describes the effect of light intensity on photosynthesis.
Answer: A
Explanation:
In plants and other primary producers, photosynthesis is a biological mechanism that is vital to energy production. Energy-containing carbohydrates are derived from light, water and carbon dioxide in the form of glucose molecules.
The waste product oxygen is released as a result. Photosynthesis depends on many variables, including:
carbon dioxide concentration,
ambient temperature
and light intensity
It is a rate-limited reaction. Since photons or particles of light provide the energy required for the reaction, high intensities of light increase the photosynthetic rate. From the graph shown, as the intensity increases steadily, so does the rate- but at too high of an intensity, it ceases to affect the rate of photosynthesis, which becomes constant or plateaus.
Beyond this point, either the supply of carbon dioxide or the temperature limits the reaction. For instance, at high intensities tissues may even be damaged by high temperatures or heat.
