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TLS Online TPP Program

#Question id: 1260

Which of the following statement regarding RTK/Ras pathway is incorrect?

#Unit 4. Cell Communication and Cell Signaling

  1. Receptor activation leads to re-localization of Sos from the cytosol to the membrane, which brings Sos close to its substrate, Ras∙GDP, which is already bound to the plasma membrane by means of a covalently attached lipid.

  2. Binding of Sos to Ras∙GDP leads to conformational changes in the switch I and switch II segments of Ras, thereby opening the binding pocket for GDP so it can diffuse out.

  3. The SH2 domains in GRB2 selectively bind to proline-rich sequences in Sos; different SH3 domains in other proteins bind to proline-rich sequences distinct from those in Sos.

  4. Ras is activated by the exchange of GDP for GTP. Active Ras∙GTP binds to the N-terminal regulatory domain of Raf, a serine/threonine kinase, thereby activating its kinase activity.

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TLS Online TPP Program

#Question id: 5655

#Unit 5. Developmental Biology

What is the "acrosomal reaction"?
TLS Online TPP Program

#Question id: 5654

#Unit 5. Developmental Biology

Two human disorders, Prader-Willi syndrome and Angelman syndrome, occur when a small deletion in a specific region of chromosome 15 is contributed by either the father or mother, respectively. Why does this small deletion not behave as a recessive allele for either syndrome, that is, why is its loss not made up for by the good copy of the region on chromosome 15 contributed by the other parent?
TLS Online TPP Program

#Question id: 5653

#Unit 5. Developmental Biology

Why is meiosis required for germ cell formation, yet is never used by somatic cells?
TLS Online TPP Program

#Question id: 5652

#Unit 5. Developmental Biology

What generalization can be applied to the pole plasm of Drosophila, the P-granules of C. elegans, the yolk-free vegetal cytoplasm of Xenopus, and the localized mRNA for vasa in zebrafish?
TLS Online TPP Program

#Question id: 5651

#Unit 5. Developmental Biology

Growth and development of plant parts involves ________.

I) cell division to produce new cells

II) enlargement and elongation of cells

III) specialization of cells into tissues
TLS Online TPP Program

#Question id: 5650

#Unit 5. Developmental Biology

Thalidomide, now banned for use as a sedative during pregnancy, was used in the early 1960s by many women in their first trimester of pregnancy. Some of these women gave birth to children with limb and organ deformities, suggesting that the drug most likely influenced ________.