Enzymes and Energetics Quiz

Enzymes and Energetics

• Enzymes are biological catalysts that speed up chemical reactions by lowering activation energy (Ea)
• Enzymes lower Ea by:
  • Aligning substrate functional groups for reactions (e.g., dehydration)
  • Stretching substrate bonds, straining them (e.g., hydrolysis)
  • Creating microenvironments with altered pH

Enzyme Affinities and Cycles

• Enzymes have specific affinities for substrates due to their shape matching the enzyme's active site
• One enzyme typically interacts with one or a few substrates
• The enzyme-substrate complex changes shape during catalysis
• Enzymes are not consumed during catalysis, allowing for repeated cycles
• Enzyme activity is influenced by the ratio of substrate concentration to available active sites

Optimization and Inhibition

• Enzyme activity is optimized by factors like:
  • Cofactors (ions)
  • Coenzymes (e.g., NAD+)
  • Optimal temperature, pH, and salinity
• Enzyme inhibition occurs through competition (blocking the active site) or non-competition (deformation of the active site)
• Inhibition can be reversible or irreversible

Activators and Inhibitors

• Allosteric activators stabilize the active form of allosteric enzymes (4° proteins)
• Allosteric inhibitors stabilize the inactive form of allosteric enzymes

Feedback Inhibitors

• Feedback inhibition occurs when products of a pathway inhibit enzymes involved in earlier reactions
• Often happens through reversible non-competitive inhibition

Biochemical Pathways

• A biochemical pathway is a series of linked chemical reactions
• Products of one reaction become reactants for the next
• Enzymes catalyze reactions within these pathways

Mevalonate Pathway

• Cholesterol is synthesized through the mevalonate pathway
• HMG-CoA to mevalonic acid is a rate-limiting step

Rate-Limiting Reactions

• The slowest reaction in a pathway is the rate-limiting step
• Often targeted by pharmaceuticals to modify pathways (e.g., statins inhibit HMG-CoA reductase, reducing cholesterol synthesis)

Basics About Energy

• Energy is the capacity to do work
• It can change the position, composition, and temperature of matter
• Energy exists in two states:
  • Potential energy: stored energy with the capacity to do work (e.g., membrane potential)
  • Kinetic energy: actively doing work
• Different forms of energy exist: solar, electrical, mechanical, chemical, and heat
• Chemical energy is stored within chemical bonds and released when bonds break

Thermodynamic Laws

• Thermodynamics studies energy transfer and transformation
• First Law: Energy can be transformed and transferred but not created or destroyed
• Photosynthesis converts solar energy into chemical energy (sugars) in chloroplasts
• Cellular respiration converts chemical energy in sugars to ATP in mitochondria
• ATP powers biological work (e.g., active transport)
• No energy transformation is 100% efficient, some energy is lost as heat

Second Law

• Energy transfer during transformations increases entropy (disorder) in the universe
• Harnessing energy for biological work is required to maintain order
• Heat has limited ability to perform biological work and contributes little to maintaining order
• As "higher order" forms of energy (e.g., solar) are transformed into heat, less energy remains available for biological order (entropy increases)

Gibbs Free Energy

• Free energy (G) is the energy available to do work
• ΔG is the change in free energy (GFinal - GInitial)
• Exergonic reactions release energy (-ΔG) and are spontaneous (occur without external energy)
• Endergonic reactions require energy (+ΔG) and are not spontaneous

Cells Transforming Energy

• Photosynthesis is overall endergonic, requiring solar energy
• Cellular respiration is exergonic, releasing free energy from glucose
• Some energy from glucose is used to produce ATP, while some is lost as heat

Don't Equilibrate to Live

• Many chemical reactions are reversible and reach equilibrium (equal rates of forward and reverse reactions)
• Equilibrium is unfavorable for living organisms as ΔG = 0 (no free energy for work)
• Living organisms maintain negative ΔG to perform work, a state called metabolic steady state

Test your understanding of enzymes and their role as biological catalysts in chemical reactions. This quiz covers various aspects, including enzyme affinities, optimization, inhibition, and the energetics involved in enzymatic processes. Challenge yourself with questions about how enzymes function and the factors that influence their activity.