Which of the following reaction of glycolysis is irreversible

1. Glucose is converted to glucose 6-phosphate in the presence of the enzyme hexokinase.

2. Fructose 6-phosphate is converted to fructose 1,6-biphosphate in the presence of the enzyme phosphofructokinase.

3. Phosphoenolpyruvate is converted to pyruvate in the presence of the enzyme pyruvate kinase.

4. isomerization of glucose 6-phosphate to fructose 6-phosphate

#Question id: 1197

#Unit 4. Cell Communication and Cell Signaling

In a signal transduction pathway, what is passed from the upstream member of the pathway to the downstream member?

#Question id: 1198

#Unit 4. Cell Communication and Cell Signaling

Both epinephrine and glucagon bind to G protein-coupled receptors and activate glycogen breakdown. Therefore, epinephrine and glucagon must:

#Question id: 1199

#Unit 4. Cell Communication and Cell Signaling

If you break liver cells by homogenization, separate the broken cell membranes (particulate) from the cytoplasm (soluble), and add epinephrine to the soluble portion, the result will be:

#Question id: 1200

#Unit 4. Cell Communication and Cell Signaling

Glucagon binds to the glucagon receptor, which interacts with a membrane-bound G protein, whose α subunit releases GDP and binds GTP. The α subunit then dissociates from the G protein and diffuses to a membrane-bound adenylyl cyclase which produces cAMP. In this scenario, name the

(1) transducer,

(2) effector,

(3) first messenger, and

(4) second messenger.

#Question id: 1201

#Unit 4. Cell Communication and Cell Signaling

Epinephrine binds to the same type of receptors in liver, fat, and smooth muscle cells. Yet in liver, glycogen breaks down; in fat, triacylglycerols break down; and smooth muscle cells relax. How can the same hormone produce three such different responses?

#Question id: 1202

#Unit 4. Cell Communication and Cell Signaling

G proteins are said to be self-inactivating. What G-protein function accounts for this?