4.1.2 Phosphorylated Intermediates

Question 1

ATP

Answer 1

• the major energy currency of the cell. When the high-energy bond in ATP is broken, energy is released.
• Energy released from the hydrolysis of ATP can be coupled to endergonic reactions in the form of phosphorylated intermediates.
• First, as ATP is hydrolyzed, glutamic acid is phosphorylated. The phosphorylated glutamic acid is then added to ammonia to produce glutamine. The phosphate is released. The net ∆G of the coupled reactions is negative.
• Keep in mind that enzymes are directing these reactions! Without enzymes none of this would happen.

Question 2

Phosphorylated intermediates

Answer 2

• used to drive different types of work within the cell.
  • Membrane proteins are phosphorylated to pump materials across the membrane.
  • Motor molecules are phosphorylated to cause movement (as in the movement of flagella and movement within muscle tissue).
  • Many chemical reactions are driven through phosphorylated intermediates (as seen in the synthesis of glutamine, illustrated below).

Question 3

note

Answer 3

• An endergonic reaction has a positive ∆G. A reaction that has a positive ∆G needs an input of energy to drive it; thus, it will not occur spontaneously.
• The synthesis of glutamine is an example of an endergonic reaction.

Question 4

True or false?

ATP acts as a phosphorylated intermediate used to fuel exergonic reactions.

Answer 4

• false

Question 5

Which molecule in the reaction pathway provided is the phosphorylated intermediate?
X–OH + ATP → X–O–P + ADP

A–H + X–O–P → A–X + Pi

Answer 5

• X–O–P
• X–O–P is phosphorylated intermediate. X–OH is phosphorylated as ATP is hydrolyzed, forming X–O–P and ADP. X–O–P then loses its phosphate group to form the final product, A–X

Question 6

Which of the following reactions could be coupled to an endergonic reaction with a delta G of +2.45 kJ / mole?

Answer 6

• a reaction with a delta G of −5.34 kJ / mole.
• A reaction with a delta G of 2.45 kJ / mole could be coupled to a reaction with a delta G of −5.34 kJ / mole because the net reaction would have a negative delta G; thus it would be exergonic.

Question 7

Phosphate group transfers from ATP to other molecules are __________ mechanisms for delivering energy.

Answer 7

• rapid, renewable, and almost universal mechanisms

Question 8

A coupled reaction takes place when

Answer 8

• the energy released from one reaction is used to fuel another.