Lec 8: Thermodynamics and metabolic reactions

Energy Released by Hydrolysis of ATP

• The hydrolysis of ATP involves the reaction of ATP with water (H₂O).

  • Reaction representation:

  • P-P-P-Adenosine (ATP) → P-P-Adenosine (ADP) + ℗₁ + ℗¡ + Energy

• ATP (Adenosine triphosphate) is converted to ADP (Adenosine diphosphate) and inorganic phosphate, releasing energy in the process.

Sodium-K+ ATPase Cycle

Step 1

• Three (3) Na+ ions bind to the sodium-potassium ATPase enzyme.

  • ATP is utilized to add a phosphate group to the enzyme.

Step 2

• Upon phosphorylation, three (3) Na+ ions are ejected outside of the cell.

• Two (2) K+ ions then bind to sites exposed in the now open channel.

Step 3

• The phosphate group is cleaved from the enzyme, returning it to a resting state.

• This process exposes K+ ions to the cell interior.

Ion-Coupled Transport by Glucose-Na+ Symporter

• Mechanism involves the use of Na+ electrochemical gradient.

• Two states involved:

  • State A: Na+ binds to the transporter protein.

  • State B: Glucose is transported into the cell alongside Na+ ions.

• Transport occurs across the membrane from the extracellular space into the cytosol.

Ion Channels in Nerve Cells

Types of Ion Channels

• Voltage-gated Channels: Open or close in response to changes in membrane potential.

• Ligand-gated Channels: Require the binding of a ligand (extracellular signaling molecule) to open.

Voltage-Gated Channel Cycle

• The cycle involves four states:

  • Closed → Open → Inactivated → Resting

Thermodynamics and Life

First Law of Thermodynamics

• Energy is conserved in the universe; it cannot be created or destroyed, only transformed.

Second Law of Thermodynamics

• Every energy transfer increases the universe's entropy (disorder).

• Living cells convert organized energy to heat, aligning with the second law.

Spontaneous and Non-Spontaneous Processes

• Spontaneous Processes: Occur without energy input, can vary in speed.

• Although life can decrease entropy locally, total entropy of the universe increases.

Free-Energy Change, ∆G

Definition

• The equation relating free energy (∆G), enthalpy (ΔH), entropy (ΔS), and temperature (T):

  • $<br>∆G = ∆H - T∆S<br>$

• Only processes with a negative ∆G are spontaneous.

Actions Resulting in a Negative ∆G

• More free energy (higher G) corresponds to less stability.

• Spontaneous changes lead to:

  • Decrease in free energy of the system (∆G < 0).

  • Increased stability of the system.

  • Free energy harnessed to perform work.

Metabolic Pathways

Catabolic Pathways

• Involve the breaking down of molecules to produce useful forms of energy.

• Generate heat, contributing to the entropy of the universe.

Anabolic Pathways

• Use energy to synthesize complex molecules from simpler ones.

• Require an energy input for biosynthesis.

Exergonic vs. Endergonic Reactions

Exergonic Reactions

• Release energy and are spontaneous (∆G < 0).

Endergonic Reactions

• Require energy input and are non-spontaneous (∆G > 0).

Energetically Favorable Reactions

• The energy of products is less than the energy of reactants; hence, the reaction can be spontaneous.

• Conversely, energetically unfavorable reactions (X → Y) can only proceed if coupled to a favorable reaction.

Photosynthesis and Cellular Respiration

Photosynthesis Reaction

• $ext{CO}<em>2 + ext{H}</em>2 ext{O} ightarrow ext{O}_2 + ext{Sugars}$

  • Converts sunlight energy into chemical bond energy.

Cellular Respiration Reaction

• $ext{Sugars} + ext{O}<em>2 ightarrow ext{H}</em>2 ext{O} + ext{CO}_2$

  • Releases energy stored in sugars via oxidation.

Harnessing Energy for Work

Kinetic and Potential Energy

• Kinetic energy from falling objects can be transformed into heat or used for work.

  • Example: Lifting a bucket of water utilizes kinetic energy efficiently, with some energy converted to heat.

ATP Hydrolysis and Biosynthesis of Glutamine

• Activation Step: Conversion of glutamic acid (Glu) to glutamine through varying free energies.

  • $∆G_{Glu} = +3.4 ext{kcal/mol}$

  • Hydrolysis of ATP provides enough energy to drive this reaction through coupling.

  • $ext{Net } ∆G = -3.9 ext{kcal/mol}$ showing favorable energy change.

Polymer Production through ATP Hydrolysis

Energy Sources for Synthesis

• Biopolymers: Nucleic acids, Polysaccharides, Proteins

  • Utilize energy from nucleoside triphosphate hydrolysis for their formation.

  • Glucose forms glycogen via ATP hydrolysis, while proteins use amino acids for synthesis.

  • Energy transformation occurs routinely in cellular processes, highlighting the importance of ATP as an energy currency.