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TLS Online TPP Program

#Question id: 23849

Which pathway regulates the contraction of vertebrate smooth muscle? 

#Unit 2. Cellular Organization
  1. When the Ca2+ level rises → Ca2+ binds CaM→ MLC kinase becomes inactive → dephosphorylates the myosin LC → unfolds the myosin II→ assemble into bipolar filaments for contraction. 
  2. When the Ca2+ level rises→Ca2+ binds CaM→activates MLC kinase→ phosphorylates the myosin LC→unfolds the myosin II → assemble into bipolar filaments for contraction. 
  3. When the Ca2+  returns to its resting level → Ca2+ binds CaM → activates MLC kinase→ phosphorylates the myosin LC → unfolds the myosin II→ causing muscle contraction.
  4. When the Ca2+ level rises→ Ca2+ binds CaM→ activates MLC kinase → phosphorylates the myosin LC → myosin adopts a folded conformation→ assemble into bipolar filaments for contraction. 
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TLS Online TPP Program

#Question id: 30105

#Unit 1. Molecules and their Interaction Relevant to Biology

Methotrexate is an inhibitor of dihydrofolate reductase. Administration of methotrexate would inhibit:
1. de novo synthesis of UMP.
2. conversion of dUMP to dTMP.
3. conversion of IMP to GMP.
4. de novo synthesis of IMP
TLS Online TPP Program

#Question id: 30106

#Unit 1. Molecules and their Interaction Relevant to Biology

If a cell has an adequate supply of adenine nucleotides but requires more guanine nucleotides for protein synthesis:

1. Glutamine-PRPP amidotransferase will not be fully inhibited.
2. AMP will be a feedback inhibitor of the condensation of IMP with aspartate.
3. ATP will stimulate the production of GMP from IMP.
4. ATP will inhibit nucleoside diphosphate reductase.
TLS Online TPP Program

#Question id: 30107

#Unit 1. Molecules and their Interaction Relevant to Biology

Major controls of de novo AMP synthesis include:

1. allosteric inhibition by GMP.
2. allosteric inhibition by AMP.
3. availability of PRPP.
4. stimulation by GTP.
TLS Online TPP Program

#Question id: 30108

#Unit 1. Molecules and their Interaction Relevant to Biology

Aspartate plays a role in all of the following EXCEPT:
TLS Online TPP Program

#Question id: 30109

#Unit 1. Molecules and their Interaction Relevant to Biology

Allopurinol is an inhibitor of xanthine oxidase. Administration of allopurinol to a patient with gout and normal HG-PRT levels would be expected to lead to all of the following EXCEPT:
TLS Online TPP Program

#Question id: 30110

#Unit 1. Molecules and their Interaction Relevant to Biology

The ribose phosphate group of purine nucleotide is taken from which compound?