Energy Basics
What form of energy is stored in chemical bonds and released during catabolism?
Chemical energy
According to the first law of thermodynamics, energy cannot be created or destroyed. What can it do instead?
Be transformed or transferred
What term refers to the portion of a system’s energy available to do work under constant temperature and pressure?
Free energy (G)
ATP consists of adenine, ribose, and how many phosphate groups?
Three
What is the molecule that an enzyme binds and acts upon?
Substrate
What is the kinetic energy of molecules moving randomly called?
Heat (thermal energy)
Which property of the universe always increases during energy transfer?
Entropy
The equation ΔG = ΔH – TΔS is used to predict what?
Spontaneity of a reaction
By transferring what group does ATP power endergonic reactions?
A phosphate group
What type of inhibition occurs when an inhibitor binds to the active site and blocks the substrate?
Competitive inhibition
Why does a diver at the top of a platform have more potential energy than one floating in the water?
Because of elevated position in a gravitational field
What term describes a process that increases entropy and requires no input of energy?
Spontaneous process
Why can a reaction with a negative ΔG still fail to occur rapidly in a cell?
Because the activation energy (EA) barrier is too high
What does ATP become after it is hydrolyzed and releases energy?
ADP and inorganic phosphate (Pi).
Why does cooperativity in multi-subunit enzymes increase efficiency of substrate binding?
Because binding of one substrate stabilizes the active conformation, increasing affinity at other sites
When glucose is broken down in a cell, chemical energy is transformed into what two main usable forms?
ATP and heat
Why does metabolism in cells never reach equilibrium?
Because cells are open systems with constant flow of energy and materials
At equilibrium, what is the value of ΔG, and what does that mean for the reaction’s ability to do work?
ΔG = 0; no free energy available to do work
What happens to an enzyme if the temperature or pH moves far outside its optimal range?
The enzyme denatures and loses activity.
What is the difference between competitive and noncompetitive inhibition?
Competitive blocks the active site; noncompetitive binds elsewhere and changes enzyme shape
A cell converts glucose into ATP, heat, and CO₂. Explain how this transformation demonstrates both the first and second laws of thermodynamics.
First law: energy conserved (chemical → ATP/heat); second law: entropy increases (heat and disorderly molecules released)
In an isolated system, what state do reactions eventually reach where no work can be done?
Equilibrium
Why can only reactions far from equilibrium perform work in cells?
Because at equilibrium ΔG = 0, so no free energy is available; far-from-equilibrium reactions have negative ΔG and can release energy.
Explain why enzymes affect reaction rate but not ΔG.
Enzymes lower EA, making reactions faster, but they don’t change the overall energy difference between reactants and products
Why does feedback inhibition save the cell energy and resources?
Because the final product shuts down its own pathway, preventing overproduction of molecules the cell already has enough of.