Arrange the events listed below in order according to the signal hypothesis:

I. Signal sequence binds to SRP

II. Translation stops

III. Translation starts

IV. Ribophorins anchor complex

V. SRP dissociates; GTP hydrolyzed

VI. SRP-signal complex binds to docking protein

#Question id: 1509

#Unit 4. Cell Communication and Cell Signaling

Cells that are infected, damaged, or have reached the end of their functional life span often undergo "programmed cell death." This controlled cell suicide is called apoptosis. Select the appropriate description of this event on a cell's life cycle.

#Question id: 1510

#Unit 4. Cell Communication and Cell Signaling

Match the correct protein (Column I) with their function (Column II) during apoptosis.

#Question id: 1511

#Unit 4. Cell Communication and Cell Signaling

Most tumors induce the formation of new blood vessels that invade the tumor and nourish it, a process called angiogenesis. Following statements are regarding to angiogenesis.

A. Angiogenesis allow the tumor to increase in size and thus increase the probability that additional harmful mutations will occur.

B. Angiogenesis also facilitates the process of metastasis.

C. The VEGF receptors, which are tyrosine kinases, regulate several aspects of angiogenesis such as endothelial cell survival and growth, endothelial cell migration, and vessel wall permeability.

D. VEGF expression can be induced by oncogenes and by hypoxia, defined as a partial pressure of oxygen of more than 7 mmHg.

E. A transcription factor VEGF is activated in low-oxygen conditions and which binds to and induces transcription of the HIF-1 gene which  affect the probability of tumor growth by angiogenesis.

Which of the following statements are incorrect?

#Question id: 1512

#Unit 4. Cell Communication and Cell Signaling

There is evidence that the accumulation of abnormal or damaged proteins due to impairment of the pathway contributes to a number of neurodegenerative diseases, including Alzheimer’s. In contrast, deliberately blocking the pathway in cancer cells could lead to a disruption of protein regulation that in turn could cause the apoptosis of the malignant cells. Accordingly, proteasome inhibitors have been developed for evaluation as anti-tumour agents against selected cancers. Bortezomib is one such inhibitor that targets the 26S proteasome, and in combination with other chemotherapeutic agents has been shown to have therapeutic potential. In contrast to the long-term control, there are several mechanisms by which the activity of an enzyme can be altered almost instantaneously:

A. Reversible inhibition by small molecules (drugs)

B. Product inhibition

C. Allosteric regulation

D. Reversible covalent modification

Which of the above mechanism follow the process of negative-feedback control and ADP-ribosylation respectively?

#Question id: 1513

#Unit 4. Cell Communication and Cell Signaling

The kinase activity of ATM is activated in response to DNA damage due to various stresses (e.g., UV irradiation, heat). Activated ATM then triggers following pathways leading to arrest in G1.

A. Chk2 is phosphorylated and, in turn, phosphorylates Cdc25A, thereby marking it for degradation and blocking its role in CDK2 activation.

B. Phosphorylation of p53 stabilizes it, permitting p53-activated expression of genes encoding proteins that cause arrest in G1, promote apoptosis, or participate in DNA repair.

C. Controlling the pool of p53, ATM phosphorylates MDM2 to inactivate it, causing increased stabilization of p53. Another protein p14ARF inhibits the activity of Mdm2 thus stabilizing p53.

Based on the above information, which one of the following statements is correct?

#Question id: 1514

#Unit 4. Cell Communication and Cell Signaling

Following statements are regarding to multiple signaling pathways in vertebrate cells that regulate outer mitochondrial membrane permeability and apoptosis.

A. In healthy cells, the anti-apoptotic protein Bcl-2, or its homolog Bcl-xL, binds to Bak or Bax pro-apoptotic proteins, blocking the ability of Bak or Bax to oligomerize and form pores in the outer mitochondrial membrane.

B. The presence of specific trophic factors (e.g., NGF) leads to activation of their cognate receptor tyrosine kinases (e.g., TrkA) and inactivation of the PI-3 kinase–PKB (protein kinase B) pathway.

C. PKB phosphorylates Bad, and phosphorylated Bad forms a complex with a cytosolic 14-3-3 protein. This sequestered Bad is unable to bind to Bcl-2.

D. In the absence of trophic factors, nonphosphorylated Bad binds to Bcl-2, releasing Bax and Bak and allowing them to form oligomeric membrane pores and holes.

E. DNA damage or ultraviolet irradiation leads to induction of synthesis of the BH3-only Puma protein. Puma binds to Bak and Bax as well as to Bcl-2, allowing Bak and Bax to form oligomeric pores.

F. Removal of a cell from its substratum disrupts integrin signaling, leading to release of the BH3-only Bim protein from the cytoskeleton. Bim also binds to Bak and Bax to promote pore formation.

Which of the following is incorrect?