#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?
#Question id: 1515
#Unit 4. Cell Communication and Cell Signaling
Following statements are regarding to metastasis (using breast carcinoma cells as an example).
A. Cancer cells leave the main tumor and attack the basement membrane, using extracellular matrix (ECM) fibers to reach the blood vessels.
B. The cancer cells can be attracted by signals such as epidermal growth factor (EGF), which can be secreted by macrophages.
C. At the blood vessels they penetrate the layer of endothelial cells that forms the vessel walls and enter the bloodstream.
D. Carcinoma cells penetrate the extracellular matrix and blood vessel wall by extending “invadopodia,” which produce matrix metalloproteases and other proteases to open up a path.
Which of the following statement shows process of angiogenesis?
#Question id: 1516
#Unit 4. Cell Communication and Cell Signaling
A research team is working on the design of a new drug for the treatment of lung cancer. To be most effective, this drug must specifically enter the cytoplasm of lung cells while not entering the cells of other tissues. Which of the following characteristics would likely enhance the specificity of this drug?
#Question id: 1517
#Unit 4. Cell Communication and Cell Signaling
Following statements are regarding to cell death and its regulation.
A. In mammals, apoptosis can be triggered by oligomerization of Bax or Bak proteins in the outer mitochondrial membrane, leading to efflux of cytochrome c and SMAC/DIABLO proteins into the cytosol; these proteins then promote caspase activation and cell death.
B. Direct interactions between pro-apoptotic and anti-apoptotic proteins lead to cell death in the absence of trophic factors.
C. Direct interactions between pro-apoptotic and anti-apoptotic proteins lead to cell death in the presence of trophic factors.
D. Once activated, apoptotic proteases called caspases cleave specific intracellular substrates, leading to the demise of a cell.
Which of the following statements are correct?
#Question id: 1518
#Unit 4. Cell Communication and Cell Signaling
Following statements are regarding to the some cancers harbor characteristic chromosome alterations. Chronic myelogenous leukemia (CML), a common leukemia in humans, was found to be associated with the Philadelphia chromosome.
A. Philadelphia chromosome is generated by a translocation between chromosomes 22 and 9. The two chromosomes exchange their terminal regions, which leads to a characteristic alteration in the size of chromosome 9.
B. At the breakpoint of this translocation, a new fusion protein, the BCR-ABL fusion, is generated.
C. The BCR-ABL fusion protein is a constitutively active kinase that phosphorylates multiple signal-transducing proteins.
D. If this translocation occurs in a hematopoietic cell in the bone marrow, the activity of the chimeric BCR-ABL oncogene dephosphorylate proteins thereby activating many intracellular signal-transducing proteins.
Which of the following statements are incorrect?