Which of the following statements about intraflagellar transport (IFT)(鞭毛内运输) is correct:
A. ransport of the particles to the flagellum tip is dependent on kinesin-2, whereas transport toward the base is mediated by cytoplasmic dynein.
B. Dynein can be carried to the tip as cargo on the anterograde-moving particles, powered by kinesin-2.
C. Inactivation of dynein would prevent recycling of the activated kinesin-2 back to the base of the flagellum.
D. All of the above.
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Which statement is not true?
All second messengers are water-soluble and diffuse freely through the cytosol.
B. In the regulation of molecular switches, protein kinases and guanine nucleotide exchange factors (GEFs) always turn proteins on, whereas protein phosphatases and GTPase-activating proteins (GAPs) always turn proteins off.
C. Most intracellular signaling pathways provide numerous opportunities for amplifying the responses to extracellular signals.
D. Protein tyrosine phosphatases display exquisite specificity for their substrates, unlike most serine/threonine protein phosphatases, which have rather broad specificity.
The major families of cell surface adhesion molecules include：
A. cadherins and selectins.
B. integrins.
C. the Ig-superfamily.
D. all of the above
CAK (CDK-activating kinase) can phosphorylate CDKs and inhibit the catalytic activity of the CDKs
The gradual loss or weakening of the functions of cohesins in oocytes of aged women contributes to high rate of trisomies (染色体三体) in fetuses (胎儿) and newborns (新生儿)
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