Adenosine Triphosphate (ATP)

Question 1

Fritz Lippmann

Answer 1

discovered ATP and coenzyme A

Question 2

What is ATP

Answer 2

a nucleotide comprised of a base (adenine), sugar (ribose), and 3 phosphate groups
- knows as cellular “energy currency”

Question 3

how do cells use ATP

Answer 3

• cells break down nutrients and use the available free energy to synthesize ATP from ADP
• ATP then donates energy to endergonic processes that require input of energy

Question 4

the large free-energy change for hydrolysis of ATP

Answer 4

• the energy-requiring / releasing processes take place at the phosphates of ATP
• hydrolysis releases the electrostatic repulsion among the negative charges
• the product inorganic phosphate has greater resonance stabilization than does ATP
• the ADP2- product rapidly ionizes to release a proton into a medium of very low [H+]

Question 5

hydrolysis of ATP to ADP

Answer 5

• the link between the gamma and beta phosphate is broken
• nucleophilic attack of the gamma phosphate
• yields ADP and Pi releasing 30kJ of energy

Question 6

hydrolysis of ATP to AMP

Answer 6

• the link between alpha and beta phosphate is broken
• nucleophilic attack of the alpha phosphate
• yields AMP and PPi which is quickly hydrolyzed to 2Pi by pyrophosphatase
• free energy is twice as large as ADP

Question 7

Mechanism of glutamine synthetase

Answer 7

the reaction of glutamine synthesis is coupled with ATP hydrolysis
- ATP reacts with glutamate to produce a mixed anhydride intermediate of phosphate and glutamate
- NH3 then as a nucleophile reacts with the electrophile carbonyl carbon atom Pi, the leaving group, is displaced

Question 8

how does ATP provide energy through group transfer

Answer 8

it is chemically versatile and can participate in many chemical reactions with different functional groups by transferring a PPi or AMP moiety to a substrate or amino acid of a reducing enzyme