Predict the consequences of a mutation in which the phosphorylation of the β-catenin protein is blocked.
A. β-catenin levels will increase and β-catenin will be constitutively active.
B. β-catenin levels will increase and β-catenin will be inactive.
C. β-catenin levels will decrease.
D. β-catenin will remain constant but cells will be unresponsive to Wnt signaling.
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Movement of phospholipids from one leaflet to the other
A. occurs routinely
B. requires cholesterol.
C. requires flippases
D. is impossible.
Which of the following is NOT the physiological role of apoptosis during normal development?
A. to prevent webbed hands and embryonic tails
B. to prevent the existence of useless nerve connections
C. to induce inflammatory responses against foreign pathogens
D. to function in immune cell selection
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.
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.
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