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.

#Question id: 2986

#Unit 2. Cellular Organization

During ubiquitin-mediated protein degradation in various events of cell cycle, ubiquitin-protein ligases ubiquitinylate substrate proteins, marking them for degradation by proteasomes. Cyclins are degraded through the action of two different ubiquitin-protein ligases, SCF and the anaphase-promoting complex or cyclosome. Following statements are regarding to SCF and APC/C.

A. SCF controls the G1–S phase transition by degrading G1/S phase cyclins and, CDK inhibitory proteins.

B. APC/C degrades S phase and mitotic cyclins, thereby promoting the exit from mitosis.

C. SCF and APC/C are multi-subunit ubiquitin-protein ligases that belong to the RING finger family of ubiquitin protein ligases.

D. SCF and APC/C belong to the different ubiquitin-protein ligase family, their regulation is same.

E. SCF recognizes its substrates only when they are phosphorylated.

F. SCF and APC/C both recognizes its substrates only when they are phosphorylated.

Which of the following is incorrect?

#Question id: 2985

#Unit 2. Cellular Organization

Use the figure to answer the question below. The unlettered circle at the top of the figure shows a diploid nucleus with four chromosomes that have not yet replicated. There are two pairs of homologous chromosomes, one long and the other short. One haploid set is black, and the other is gray. The circles labeled A to E show various combinations of these chromosomes. What is the correct chromosomal condition for one daughter nucleus at telophase of mitosis? 

#Question id: 2984

#Unit 2. Cellular Organization

Certain unicellular eukaryotes, including diatoms and some yeasts, have mechanisms of nuclear division that may resemble intermediate steps in the evolution of mitosis. Which of the following is a characteristic feature of nuclear division in these organisms?

#Question id: 2983

#Unit 2. Cellular Organization

Cell cycle is regulated by master regulators (cyclin and CDKs). In vertebrates, G1 CDK activity rises during G1 and is stimulated by the presence of growth factors. When signaling from growth factors is sustained, the resulting cyclin D–CDK4/6 complexes begin phosphorylating Rb, releasing some E2F, which stimulates transcription of the genes encoding cyclin E, CDK2, and E2F itself. In a particular cell type there is a mutation in Rb such that it cannot be phosphorylated. What will be the correct expression pattern of cyclin E in these cells after mitotic stimulation?

#Question id: 2982

#Unit 2. Cellular Organization

Match the following proteins (Column I) with their functions (Column II) during cell cycle.

#Question id: 2981

#Unit 2. Cellular Organization

For the nuclear envelope to be broken down as cells go from prophase to prometaphase during mitosis, the nuclear lamina has to be disassembled. Which of the following statement is incorrect?