2: ATP—Cellular Energetics

Question 1

How do living organisms comply with the 2nd Law of Thermodynamics?

Answer 1

The second law of thermodynamics states that the entropy of the universe always increases in the course of every spontaneous (natural) change. In other words: over time, differences in temperature, pressure, and density tend to even out.

Life disorders its surroundings more than it orders itself by disordering light energy.

ATP drives work function returning energy to the environment as heat (IR photons)

Question 2

How are fuels ‘burned’ in controlled steps to extract energy in a usable form and amount?

Answer 2

Energy stored in reduced fuels is converted to energy stored in ATP by multiple enzyme-
controlled steps

Question 3

What makes ATP’s phosphoric acid anhydride bonds ‘energy rich’?

Answer 3

• Charge repulsion is relieved upon breaking the α-β or β-γ bonds
• Greater resonance stabilization of products, ADP + Pi or AMP + PPi
• More favorable interactions of products with water

Question 4

Why do all living things have a continual need for energy? What three work functions do
our cells need to perform to stay alive?

Answer 4

1. Mechanical work
2. Transport work
3. Biosynthetic work

Question 5

Why is ATP well suited to be the predominant ‘energy-rich’ carrier in the cell?

Answer 5

• Number of ~P (i.e., 2)
• Soluble and mobile
• High affinity binding to enzymes
• Recognition handle

See figure pg. 43

Note that enzymes lower top G(++), not bottom circle G(0).

Question 6

What are the three tiers of energy storage in the cell?

Answer 6

ATP meets our immediate energy needs; glycogen: intermediate term; fats and proteins:
long term. Hence, energy storage is a 3-tier system.

Question 7

How do enzymes employ the Common Intermediate Principle to couple energy-releasing reactions to energy-requiring reactions?

Answer 7

see pg. 44

The total ΔG°” for the two reactions is not altered by the enzyme

Question 8

What are the advantages of having a central pool of energy in the cell?

Answer 8

Due to the presence of nucleoside diphosphate kinase (NDK), the various NTP pools are able to share available energy and avoid rate-limiting steps.

Finally, the advantage of having a central pool of chemical energy rather than a number of smaller ones comes from the role that adenine nucleotides play in maintaining a proper balance between energy-producing and energy-requiring processes in the cell.

Question 9

How are ATP levels temporarily maintained under energetically stressful conditions?

Answer 9

All of these, generate short term ATP:

1. Phosphagens–Vertebrate muscle and nerve (creatine kinase)
2. Adenylate kinase–ubiquitous
3. adenylate deaminase–(liver and skeletal muscle)