ATP

Question 1

What is ATP

Answer 1

” energy currency”

• discovered by Fritz Lipmann
• it is a nucleotide, comprimises of a base (adeneine), sugar (ribose), and three phosphate groups, labelled as alpha beta and gamma

NOT a store of energy; it is a link between catabolism and anabolism

* note phosphoester bond between hydroxyl on sugar, 3 phosphoric acids create a phosphoanhydride bond (high energy bond)

Question 2

How is ATP a link between catabolism and analbolism

Answer 2

• cells break down nutrient molecules and use the availbale free energy to synthesize ATP from ADP (hydrolysing the bond)
• ATP donates its energy to endergonic processes that require energy (synthesis of metabolic intermediates and macromolecules (anabolism), active transport across membranes, mechanical motion)
• ATP turns over very rapidly in cells

Question 3

The Free energy change for hydrolysis of ATP is ____ and _____

Answer 3

Large and negative

• most hydrolysis reactions are energetically favourable, but delta G depends on nature of the bomd
• typically 15-20kJ, but with ATP get 50 kJ

(ΔG⁰ for ATP is about -50 kJ/mol, ΔG⁰′ = -30.5 kJ/mol)

• it is at the phosphates that the energy-requiring/ releasing process take plae

Question 4

What is the Chemical basis for the large free energy change associated with ATP hydrolysis

Answer 4

1) hydrolysis realeases the lectrostatic repulsion amound the negative charges
2) the product inorganic phosphate has greater resonance stabilization then does ATP
3) the ADP ^2- product rapidly ionizes to release a proton into a medium of very low [H^+] driving the hydrolysis towards completion

Question 5

How is ATP hydrolysed

Answer 5

• two phosphoanhydride bonds (high energy bonds)

1. Hydrolysis of the link between gamma and beta phosphate (nucleophilic attack of the gamma phosphate
   
   • yeilds ADP and Pi realeasing approx 30 kJ of energy
2. Hydrolysis of the alpha-beta linkage (nucleophilic attack of the alpha phosphate)
   
   • ATP -> AMP + PPi
   • in the cell PPi is immediately hydrolzyed by the action of anzyme phyrophosphatase to give two moles of Pi
   • PPi -> 2 Pi (note this ALWAYS happends)

*NET RXN: ATP -> AMP + 2Pi

*this results in hydrolysis of both phosphodiester binds of ATP

*the amount of energy required will dictate is rxn 1 or 2 will occur (most rxns only need rxn 1 )

Question 6

How does the hydrolysis of ATP drive energetically unfavourable reactions?

Question 7

Explain glutamine synthetase

Answer 7

• example of hydrolysis driving chemical reactions forward
• reaction is coupled with ATP

*note just an exmaple dw about the actual reaction

1. ATP reacts with glutamate to produce a covalent intermediate a covalent intermediate mixed anyhride of phosphate and glutamate
2. NH3 acting as a nucleophile reacts with the electrophile carbonyl carbon. Pi is then released

Question 8

How does ATP provide energy

Answer 8

• through group transfer, not hydrolysis
• ATP is chemically versatile, the phosphate group can participate in a variety of chemical reactions with common organic functinoal groups
• in addition to phosphoryl group, ATP can also transfer a pyrophosphoryl (PPi) or an adenylate (AMP moiety) to a substrate or to an amino acid reside of an enzyme, helping to drive reactions
• atp provides energy not by simple hydrolysis but thorugh group transfer