Question

1. The following question refers to regulated enzymes in glycolysis.

Here is a summary of these enzymes.
glycolysis reaction #1 is catalyzed by hexokinase
glycolysis reaction #3 is catalyzed by phosphofructokinase (PFK)
glycolysis reaction #10 is catalyzed by pyruvate kinase

Which of the following statements about glycolysis regulation in liver cells is/are TRUE?

		At high substrate concentrations, the Km of muscle hexokinase is similar to liver hexokinase.
		Liver PFK has low enzyme activity when glucagon is present.
		All of the statements are true.
		Liver pyruvate kinase activity is low when the concentrations of ATP and acetyl-CoA are low.

2. Select a word for each blank that makes a sentence which correctly compares energy yield per carbon from a fatty acid and glucose.


Oxidation of a fatty acid yields    select an answer   more   less   ATP per carbon than a glucose because there are    select an answer   more   less   C-H bonds in a fatty acid, making the    select an answer   carbons   oxygens   hydrogens   in a fatty acid more    select an answer   oxidized   reduced   .

3. Which of the following statements about triacylglycerols is/are true?

		Triacylglycerols are stored in adipose tissue.
		The three fatty tails in a triacylglycerol are most often different.
		All of the statements are true.
		A triacylglycerol is not a polymer.

4. Select whether each statement that compares muscle and liver cells is true or false.


   select an answer   true   false   Both muscle cells and liver cells can synthesize ketone bodies, but only muscle cells use them.

   select an answer   true   false   Glucose stored as glycogen in muscle and liver cells can be shared with other body cells.

   select an answer   true   false   Ketone bodies can be used as an energy source in muscle cells, but not liver cells.

5. In hormonal signaling pathways, second messenger molecules amplify signals so that

		receptor proteins can increase production of more second messengers.
		many metabolic enzymes can respond at the same.
		kinases can rapidly dephosphorylate target proteins.
		cells without hormone receptor proteins can be activated.

Answer 1

1. The statement which is true: Liver PFK has low enzyme activity when glucagon is present.

The false statements are:

• At high substrate concentrations, the Km of muscle hexokinase is similar to liver hexokinase (because liver hexokinase has higher affinity (low Km) for glucose)
• Liver pyruvate kinase activity is low when the concentrations of ATP and acetyl-CoA are low (because pyruvate kinase activity is lowered by high concentration of ATP and acetyl-CoA)

2. Oxidation of a fatty acid yields more ATP per carbon than a glucose because there are more C-H bonds in a fatty acid, making the carbons in a fatty acid more reduced.

3. The statements which are true:

• Triacylglycerols are stored in adipose tissue.
• A triacylglycerol is not a polymer.

The statement which is false: The three fatty tails in a triacylglycerol are most often different. (as the three fatty tails in triacyglycerides are both same as well as different. so no criteria for this statement)

4.

• Both muscle cells and liver cells can synthesize ketone bodies, but only muscle cells use them. (True)
• Glucose stored as glycogen in muscle and liver cells can be shared with other body cells. (True)
• Ketone bodies can be used as an energy source in muscle cells, but not liver cells. (True)

5. In hormonal signaling pathways, second messenger molecules amplify signals so that many metabolic enzymes can respond at the same.