Module 23: ATP and Cellular Work

explain how cells get energy from ATP

ATP breaks apart and releases its energy. When ATP breaks apart, it releases energy and loses a phosphate group. That means that it is now ADP.

Why does ATP hydrolysis release a lot of free energy?

ATP is unstable compared to its products.

ATP is synthesized

by using energy from photosynthesis or respiration. ATP is hydrolyzed to release energy needed for cellular work.

Complete the following sentence: The hydrolysis of one mole of ATP can be used to drive reactions that have a ΔG that is...

less than 7.3 kcal/mol.

The sodium-potassium pump is an active transport pump that uses energy to pump potassium into cells and sodium out of cells. Why is ATP energy required?

to pump the Na + and K + ions against their diffusion gradient

ATP has a high ∆G (free energy)

- ATP is less chemically stable than ADP - ADP has less electrostatic repulsion between negatively charged phosphate groups. 2 Pi groups in ADP vs. 3 Pi groups in ATP. - The released Pi has 4 oxygen atoms with partial negative charges that can be stabilized by hydrogen bonding with H2O molecules in biological systems. - These qualities make ADP and Pi much more stable than ATP.

Is ATP the only "energy molecule"?

- ATP is not the only energy carrier within cells. - ATP can release 7.3 kcal/mol. - Creatine Phosphate (CP) can release 9.6 kcal/mol. - Phosphoenolpyruvate (PEP) can release a 14.8 kcal/mol. - GTP is also an 'energy molecule'- remember GTP hydrolysis and microtubule polymerization

Recycling of ATP is necessary to meet the energy needs of our cells.

- The regeneration of ATP is very quick and efficient. - For example, human muscle cells use and regenerate approximately 10 million molecules of ATP per second per cell.

Humans require a lot of ATP

- We use approximately 50 kg of ATP each day. - Not even Olympic sprinters can store 50 kg of ATP in their muscles. - At most, they store approximately one minute's worth of ATP. - Therefore, ATP must be regenerated continuously

ATP components:

--nitrogenous base (adenine) --sugar (ribose) --three phosphate groups

DNA helicase

Repeated ATP hydrolysis powers the changes in shape that allow DNA helicase to move along DNA- breaking Hydrogen bonds as it goes

Identify the structural features found in ATP.

a nitrogenous base, a ribose sugar, and three phosphate groups

Adenosine triphosphate (ATP)

is the molecule used by cells to fulfill their energy needs. is the most widely used energy storage molecule among organisms.

Exergonic reactions (free energy in the ATP cycle):

reactions that release energy and have negative ΔG values (example: ATP hydrolysis). These are spontaneous. ATP + H2O → ADP + Pi (ΔG = -7.3 kcal/mol)

Endergonic reactions (free energy in the ATP cycle):

reactions that require an input of energy and have positive ΔG values (example: ATP synthesis) These do not begin spontaneously. ADP + Pi → ATP + H2O (ΔG = +7.3 kcal/mol)

ATP is not the only molecule that can drive reactions. When ATP is depleted during exercise, muscle cells use phosphocreatine to drive the regeneration of ATP. Consider the following half reactions: 1. ATP + H 2O → ADP + P i ΔG = -7.3 kcal/mol 2. Phosphocreatine + H 2O → creatine + P i ΔG = -10.3 kcal/mol From these two reactions, calculate the Gibbs free energy of the following coupled reaction, catalyzed by creatine kinase: Phosphocreatine + ADP → ATP + creatine ΔG = ? Which is the correct net Gibbs free energy of the reaction?

ΔG = -3 kcal/mol