2. In many cases, cellular signal transduction is mediated by a membrane-associa

Question

2. In many cases, cellular signal transduction is mediated by a membrane-associated G-protein complex. Which is not right about this protein complex?

A) The complex is made of -, -, and -subunit.

B) The Gs-subunit has a GTPase activity.

C) Depending on the receptor types, either Gs-subunit or Gi-subunit is used.

D) Signal transduction through G-proteins ultimately regulates protein phosphorylation.

E) None of the above.

3. Which statement is not right about the pyruvate dehydrogenase?

A) This enzyme is located in the mitochondria.

B) This enzyme consists of three different enzymatic subunits (E1, E2, and E3).

C) This enzyme catalyzes the reaction: Pyruvate + CoA + NAD ® Acetyl-CoA + CO2 + NADH

D) This enzyme also uses TPP (thiamine pyrophosphate), lipoic acid, and FAD as cofactors.

E) Despite its complexity, this enzyme is not an important regulation point of TCA cycle.

4. To maintain a proper rate of the TCA cycle, oxaloacetate is replenished periodically. To increase [oxaloacetate], ___X____ is turned on but the TCA cycled is turned off by phosphorylation of __Y__.

A) X = Glyoxylate cycle     ::::::     Y = isocitrate dehydrogenase

B) X = Glyoxylate cycle     ::::::     Y = isocitrate lyase

C) X = Q cycle                    ::::::     Y = isocitrate dehydrogenase

D) X = Q cycle                    ::::::     Y = isocitrate lyase

E) None of the above.

5. Assume you have three NADH and one FADH2. Calculate the total numbers of H+ pumped into the inter-membrane space and the maximal number of ATP produced inside the matrix.

A)    40 H+   and     12 ATP
B)    40 H+   and     11 ATP
C)    36 H+   and     12 ATP

D)    36 H+   and     11 ATP
E)    None of the above.

Explanation / Answer

2. D) Signal transduction through G-proteins ultimately regulates protein phosphorylation.

3. E) Despite its complexity, this enzyme is not an important regulation point of TCA cycle.

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