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Introns: Functions and Origin

Very little is known about the genomic architecture even though there is widespread proliferation of the introns. Evidences from the recent advances emerged through the large-scale genomic sequencing projects and the functional analysis of the mRNA-processing events support the idea that the spliceosomal introns were not only present in the early eukaryote but also diverged into a minimum of two eukaryotic classes in the early stages of evolution (Lynch, 2002). The origin of introns is an issue and several researchers proposed different theories on the origin of introns. The present day debate goes on the important issues of evolution such as the introns-early versus introns-late, the mini gene hypothesis, the protein-splice site hypothesis, rates of intron gain, loss, and the ratio of parallel gain. Introns are not distributed uniformly, along with the excess of phase 0 introns. The introns early theory proposes that introns were present in the last universal common ancestor (LUCA) of prokaryotes and eukaryotes (Gilbert, 1978). To say further, it is postulated that the premier genetic elements encoded small domains, similar in length to typical modern exons, which recombined via non-coding intronic sequences present in some of these elements to facilitate protein evolution (Roy, 2003). During subsequent evolutionary history, the introns underwent diverged evolutionary courses in the different lineages: they were erased in prokaryote lineages, but maintained in eukaryotes as introns through the appearance of the spliceosome (Gilbert, 1978). The loss of introns in prokaryotes has been explained as “genome streamlining” (Roy, 2003). According to the streamlining hypothesis, the replication efficiency is the cardinal object of the main pressure in the evolution of prokaryotes, and thus non-essential parts of the genomes would be eliminated. Introns would not exist under such intense negative selection.
The introns late theory supposes that spliceosomal introns arose in remotely antiquated eukaryotes from self-splicing introns. These group II introns were present in the mitochondrial organelles of endosymbionts, and invaded previously undivided genes and intron-less genomes, and the spliceosome evolved as a way to remove them (Cavalier-Smith, 1991). The argument for self-splicing introns giving rise to spliceosomal introns and the spliceosomes is based on functional and structural similarities between self-splicing group II introns and spliceosomal introns. In both types of introns, the 5? end becomes bound to an adenine near the 3? end, forming a lasso structure that is excised (Newman, 1997). Furthermore, the group II introns appear to be phylogenetically limited to eubacteria (Bonen

Venturi Meter Coefficient Discharge Experiment

Aims and Objectives: In this experiment the flow (k) and discharge (Cd) coefficients of a venturi meter will be assessed by comparing the real discharge measured in the experiment with the theoretical discharge calculated by deriving venturi discharge formula from Bernoulli and continuity equations.
The apparatus used in this experiment are:
Stopwatch – It is used to calculate the time required for a specific volume of water to be supplied, to measure the rate (actual) of flow (Qa).
Venturi apparatus – The venturi apparatus is connected at six different points to the manometer
Thermometer – Thermometer is used to measure the temperature of the water, the Reynolds number will be calculated by the resulting kinematic viscosity.
Hydraulic bench – The hydraulic bench contains water pump and tracks the volume of water collected. The jet apparatus rests on it.
Venturi Meter
Place the meter horizontally, in such a way that at point 1 and 2 the z values are the same.
Open the inlet valve and leave at it maximum flow.
Release the air from the manometer and venturi tube.
Tightly close the air purge valve on the upper manifold.
Allow the water to flow by switching on the bench supply valve.
Make sure to close apparatus control valve.
Allow some air to enter by slowly opening the spindle once more
With the stop match measure the discharge by recording the time required for a specific volume of water to be collected.
To measure the discharge use the stop watch to record the time required for a specific volume of water to be collected. (Volume of the water is measured by a meter beside the supply valve.)
Repeat this 16 times and measure the flow rate. Along with it, measure h1, h2 and h3.
h1 = Height of water in manometer tube A (inlet)
h2 = Height of water in manometer tube D (throat)