Biochemistry: Spontaneity and Thermodynamics

Spontaneity in Biochemical Reactions

• Nonspontaneous processes, also termed endergonic, require energy input to occur.
• At equilibrium, the change in free energy (ΔG) is zero, indicating no net change in the process.
• A positive ΔG (>0) signifies that a reaction is nonspontaneous and energy must be supplied.

Life and Thermodynamics

• 1st Law of Thermodynamics: Energy cannot be fully converted from one form to another without loss; energy conservation principle.
• 2nd Law of Thermodynamics: Even with perfect efficiency, complete conversion of energy is unattainable; disorder in systems increases over time.
• Free energy change relates to enthalpy (ΔH) and entropy (ΔS) through the equation: ΔG = ΔH - TΔS, where T is temperature.
• The 1st Law focuses on enthalpy changes, while the 2nd Law emphasizes entropy changes, critical for biochemistry.
• Cells expend energy to maintain structure against the natural tendency towards disorder, as spontaneous processes increase universal entropy and decrease free energy.

Cellular Structures and Functions

• The inner mitochondrial membrane has folds called cristae, creating a matrix containing enzymes for energy-yielding reactions.
• Endoplasmic Reticulum (ER) is a continuous membrane system; Rough ER has ribosomes while Smooth ER does not.
• Chloroplasts, exclusive to green plants and algae, have grana for photosynthesis and contain unique DNA.
• The Golgi apparatus consists of membranous sacs, involved in protein secretion and located near Smooth ER.

Biochemical Foundations

• All living organisms utilize the same biomolecules and energy, making biochemical processes accessible to chemical and physical study.
• Biomolecules consist of polymers formed from monomers: amino acids (proteins), nucleotides (nucleic acids), monosaccharides (polysaccharides), and glycerol with fatty acids (lipids).
• Enzymes are proteins that serve as catalysts, with their effectiveness determined by their amino acid sequence.
• The genetic code connects nucleotide sequences in nucleic acids to amino acid sequences in proteins.

Theories of Life Origin

• RNA-World Theory: Proposes RNA was the original coding molecule, able to catalyze its own processing and replication.
• Double-Origin Theory: Suggests that catalysis and coding developed independently, later integrating to form life.

Prokaryotes vs. Eukaryotes

• Prokaryotes (before nucleus): Unicellular, small (1-3 micrometers), encompass bacteria and cyanobacteria.
• Eukaryotes (true nucleus): Feature a defined nucleus with a membrane, can be unicellular (e.g., yeasts) or multicellular (e.g., plants and animals) and are larger (10-100 micrometers).
• Organelles have specialized functions and contain membranes; prokaryotic cells have only a plasma membrane, consisting of a lipid bilayer with embedded proteins.

Explore the concepts of spontaneity in biochemical reactions and the principles of thermodynamics that govern energy transformations. This quiz delves into endergonic processes, free energy changes, and the foundational laws of thermodynamics critical for understanding biochemistry. Test your knowledge on how these principles apply to living systems.