Bioenergetics and Thermodynamics Quiz

Bioenergetics and Enzymes

• Bioenergetics is the study of energy transformation in a living organism.
• Energy is the capacity to do work; change or move things.
• Thermodynamics is the study of changes of energy.

First Law of Thermodynamics

• Energy can neither be created nor destroyed but can be converted into different forms.
• For example, Chemical energy in ATP → mechanical energy for organelles to move about the cell.
• This law is represented by the equation: ∆E = Q - W
  • ∆E = change in internal energy
  • Q = heat (energy in/out)
  • W = work (energy in/out)

Second Law of Thermodynamics

• In any natural process, the total entropy (measure of randomness or disorder) of a closed system will increase or remain constant, but never decrease.
• Energy tends to spread out and systems naturally evolve towards a state of greater randomness or disorder.

Entropy

• It is a measure of randomness or disorder.
• It also reflects the tendency of energy to spread out over time in isolated systems.
• Every event is accompanied by an increase in the entropy of the universe.
• Living systems maintain a state of ‘system’ order (low entropy) at the expense of higher ‘universe’ disorder (high entropy) - through metabolism.

Gibbs Free Energy

• ΔG represents the maximum amount of work that can be performed by a system at constant temperature and pressure.
• This allows us to predict whether a chemical reaction or process will occur spontaneously.
• This is represented by the equation: ∆G = ∆H – (T x ∆S)
  • ∆H = is the change in enthalpy
  • T = Temperature in Kelvin
  • ∆S = Entropy
• If ΔG is negative, the reaction is exergonic and spontaneous - towards a state of lower energy.
• If ΔG is positive, the reaction is endergonic and requires energy input or coupling.

Enzymes

• Enzymes are biological catalysts that speed up chemical reactions in living organisms.
• They bind to specific substrates at the active site.
• They lower the activation energy required for a reaction to occur.
• Temperature and pH can affect enzymatic reaction rates.
• Each enzyme is most active under specific conditions.

Enzyme Inhibitors

• Enzyme inhibitors slow the rates of enzymatic reactions.
• Irreversible inhibitors bind tightly to the enzyme.
• Reversible inhibitors bind loosely to the enzyme.
• Competitive inhibitors compete with the substrate for the active site.
  • They resemble the substrate structure.
  • They can be overcome with high substrate/inhibitor ratios.
  • They increase Km, but do not alter Vmax.
• Noncompetitive inhibitors bind to sites other than the active site.
  • They reduce Vmax, but do not alter Km.
• They are usually reversible.

Metabolic Regulation

• Cellular activity is highly regulated.
• Enzymes are controlled by alterations in their active or allosteric sites.
  • Covalent modification of enzymes with the addition of a phosphate group (P) → protein kinases.
  • Allosteric modulation of enzymes by compounds binding to allosteric sites.
  • End-product inhibition - the product of a pathway inhibits enzymes of the pathway.

Pyruvate Dehydrogenase Kinase (PDK)

• PDK is an enzyme that inactivates pyruvate dehydrogenase by phosphorylation at specific sites.