The pressure-flow model, first proposed by Ernst Münch, Phloem loading at the source and phloem unloading at the sink establish the pressure gradient.

a.) In source tissues, an accumulation of sugars in the sieve elements generates a lower or negative solute potential (ψs).

 b.) source tissue, causes a steep drop in the water potential (ψ), due to water potential gradient, water enters the sieve elements and causes turgor pressure (ψp ) decrease.

c.) In sink tissues, phloem unloading leads to a lower sugar concentration in the sieve elements, generating a higher or less negative solute potential.

d.) As the water potential of the phloem rises above that of the xylem, water tends to leave the phloem in response to the water potential gradient, causing a decrease in turgor pressure in the sieve elements of the sink.

Which of the following statements of sink and source tissue is FALSE?

#Question id: 4114

#Unit 3. Fundamental Processes

Splice-site recognition is prone to two kinds of errors. First, splice sites can be skipped, with components bound at, for example, a given 5’ splice site pairing with those at a 3’ site beyond the correct one. Ways in which the accuracy of splice-site selection can be enhanced are as

A. The factors that recognize that site are transferred from the polymerase carboxy-terminal “tail” onto the RNA. Once in place, the 5’ splice site components are poised to interact with those other factors that bind to the next 3’ splice site to be synthesized.

B. SR (serine–arginine-rich) proteins bind to sequences called exonic splicing enhancers (ESEs) within the exons. SR proteins bound to these sites recruit the splicing machinery to the nearby splice sites to ensure correct splicing

C. By recruiting splicing factors to each side of a given exon, this process encourages the so-called “exon definition, contribute to correct splicing

D. Alternative splicing is intentional missplicing mechanism

Which of the following is INCORRECT?

#Question id: 4113

#Unit 3. Fundamental Processes

Match the transcriptional machinery with their respective RNA Polymerase

#Question id: 4112

#Unit 3. Fundamental Processes

Which of the following is the structure of the nucleotide at the branch site of a spliced intron?

#Question id: 4111

#Unit 3. Fundamental Processes

Which of the following is NOT characteristic of a eukaryotic enhancer element?

#Question id: 4110

#Unit 3. Fundamental Processes

Tay-Sachs disease belongs to the family of lysosomal storage diseases; it is an autosomal recessive neurodegenerative disorder caused by deficiency of the lysosomal enzyme hexosaminidase. The inability to degrade sphingolipids results in the deposition of these lipids in the cells that causes severe mental retardation and death in childhood. The most common mutation in Tay-Sachs disease patients is a 4-base pair insertion in exon 11 of the 14 exons of the hexosaminidase gene. What could be the most likely consequence of this mutation?

#Question id: 4109

#Unit 3. Fundamental Processes

When E. coli is grown on a medium containing a mixture of glucose and lactose, it proliferates with complex kinetics. The bacteria proliferate faster at the beginning than at the end, and there is a lag between these two phases when they virtually stop dividing. Assays of the concentrations of the two sugars in the medium show that glucose falls to very low levels after a few cell doublings, but lactose remains high until near the end of the experimental time course (not shown). Although the concentration of lactose is high throughout most of the experiment, β-galactosidase, which is regulated as part of the Lac operon, is not induced until more than 100 minutes have passed. Choose correct explanation why the Lac operon is not induced by lactose during the rapid initial phase of bacterial proliferation

A. The rapid bacterial growth at the beginning of the experiment results from the metabolism of glucose. The slower growth at the end results from metabolism of lactose.

B. CAP and the Lac repressor mediate induction in the situation

C. The bacteria stopped growing in the middle of the experiment because they ran out of glucose but did not yet possess the enzymes necessary for lactose metabolism

D. Induction of the Lac operon requires that two conditions be met: lactose must be present and glucose must be absent.