Biochemistry of Phosphagens and ATP

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Questions and Answers

What is the function of phosphagens like phosphocreatine (PC) and phosphoarginine (PA) in muscle cells?

They store glucose for energy.

They are involved in protein synthesis.

They facilitate lipid metabolism.

They act as energy-rich storage molecules. (correct)

How do phosphagens compare to ATP in terms of group-transfer potential?

They have variable group-transfer potential depending on conditions.

They have higher group-transfer potential than ATP. (correct)

They have less group-transfer potential than ATP.

They have the same group-transfer potential as ATP.

What is the primary role of ATP in energy transfer?

It creates thioesters for energy storage.

It hydrolyzes to release energy directly.

It bonds with creatine to store energy.

It transfers phosphoryl groups to other molecules. (correct)

What is unique about thioesters like acetyl-CoA compared to regular esters?

They contain a sulfur atom in place of an oxygen atom. Signup and view all the answers

What is meant by phosphoryl-group-transfer potential?

The ability to transfer a phosphoryl group to another molecule. Signup and view all the answers

In which cellular process do NADH and NADPH act as electron carriers?

Redox reactions. Signup and view all the answers

What is the significance of the large, negative standard free energy of hydrolysis of thioesters?

It permits thioesters to act as storage compounds. Signup and view all the answers

What is a correct statement about the absorption characteristic of NADH?

NADH absorbs light at 340 nm. Signup and view all the answers

What are phosphagens primarily used for in animal muscle?

To replenish ATP when needed Signup and view all the answers

What is the primary result of the reaction between luciferin and luciferase?

Emission of light Signup and view all the answers

What term is used to describe the energy contained in the high-energy phosphoanhydride bonds of ATP?

Phosphorylation potential Signup and view all the answers

Which biochemical process is NOT categorized as a reaction in living cells?

Blood coagulation Signup and view all the answers

What is the ΔG’ formula used for?

Determining free energy changes in biochemical reactions Signup and view all the answers

What is the role of pyruvate kinase in the hydrolysis of phosphoenolpyruvate (PEP)?

To catalyze the reaction Signup and view all the answers

Which of the following is NOT a function of ATP in biological systems?

Serving as a genetic blueprint Signup and view all the answers

Which of the following factors contributes to the high energy content of ATP?

Charge repulsion among phosphate groups Signup and view all the answers

Study Notes

Phosphagens

Phosphocreatine (PC) and phosphoarginine (PA) are phosphoamides
They have higher group-transfer potentials than ATP
They are produced in muscle during times of ample ATP
They are used to replenish ATP when needed via creatine and arginine kinase reaction

Energy from ATP

The actual free-energy change of ATP hydrolysis is different due to variations in conditions inside the cell
ΔG' describes the change in free energy under standard conditions
ΔG' is a function of reactant and product concentrations and of the temperature
For the reaction: aA + bB cC + dD ΔG’ = ΔGo’ + RT ln ([C]c[D]d/[A]a[B]b)
ATP provides energy by group transfers, not by simple hydrolysis
ATP can carry energy from high-energy phosphate compounds produced by catabolism to compounds such as glucose, converting them into more active forms

Phosphoryl-Group Transfer Potential

Compounds that can transfer a phosphate group have a phosphoryl-group-transfer potential
Energy-rich compounds have group transfer potentials equal to or greater than that of ATP
Low-energy compounds have group transfer potentials less than that of ATP

Key Reactions in Cells

Cells have the capacity to carry out thousands of specific enzyme-catalyzed reactions
Reactions in living cells include: oxidation-reduction, group transfer, H2O addition/removal, formation of a double bonds, isomerization, making and breaking C-C bonds

How Cells Obtain Energy

Cells need energy to do all their biological work
This energy comes from the oxidation of metabolic fuels
The free energy of ATP helps to generate and maintain a highly ordered structure, generate motion (mechanical work), generate concentration and electrical gradients across cell membranes (active transport), and generate heat and light

Hydrolysis of Phosphoenolpyruvate (PEP)

PEP is a high-energy phosphate compound
The hydrolysis of PEP is catalyzed by pyruvate kinase
Hydrolysis of PEP is followed by spontaneous tautomerization of the product pyruvate
Tautomerization is not possible in PEP, and thus the products of hydrolysis are stabilized relative to the reactants
This stabilization leads to a large negative free-energy change

NADH and NADPH

NADH and NADPH act with dehydrogenases as soluble electron carriers
They are derived from vitamin niacin (source of the nicotinamide)
NADH absorb at 340 nm

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Description

This quiz covers the key concepts related to phosphagens like phosphocreatine and phosphoarginine, their roles in ATP replenishment, and the energy dynamics of ATP hydrolysis. You'll learn about the free-energy changes associated with ATP and how phosphoryl groups are transferred within the cell. Test your understanding of energy metabolism and biochemical reactions!