Midterm 1: Lec 5 Energy Slides Flashcards
What’s the difference between kinetic and potential energy?
Kinetic energy is work-associated; potential energy is stored energy
Where is energy from the sun stored?
Stored as potential energy in chemical bonds of sugar molecules formed by photosynthesis
First law of thermodynamics
Energy cannot be created or destroyed; it can only be converted from one form to another
Second law of thermodynamics
In any energy interconversion, some energy is released as heat, which adds to the entropy of the system
What happens as energy is utilized?
More and more of it is converted to heat
Metabolism
Sum of all chemical processes occurring within a cell or organism
Metabolic pathway
Product of one reaction becomes reactant in the next (series of reactions)
Equilibrium constant (Keq)
Ratio of the concentration of products and reactants at equilibrium (high Keq means reaction goes far towards the right, or completion)
What changes Gibbs free energy?
Breaking of chemical bonds in the course of chemical reactions
What is the equation for ∆G?
∆G = ∆H - T∆S
-remember that ∆G indicates nothing about rxn rate
Exergonic reaction
Products contain less free energy than reactants (negative ∆G) - occur spontaneously and release heat
Endergonic reaction
Products contain more energy than reactants; need energy for reaction to happen
What does a ∆G value near zero mean?
Reaction is readily reversible
What does a large negative ∆G mean?
Reaction that goes almost to completion
What does ATP hydrolysis release? What’s the equation?
Releases large amounts of energy
Equation is: ATP + H2O = ADP + Pi + energy
What does the synthesis of ATP from ADP and Pi require?
Energy
Where does the body store carbohydrates and lipids?
Carbs in glycogen; lipids in triglycerides
∆G for ATP hydrolysis in standard vs. cell conditions
Standard: -7 kcal/mol
Cell: -12 kcal/mol (textbook says -14)
What are the exergonic reactions in the energy-coupling ATP cycle?
Cell respiration and catabolism
What are the endergonic reactions in the energy-coupling ATP cycle?
Active transport, cell movements, anabolism
Equation for firefly bioluminescence
Luciferin + O2 = ATP; releases light
What are the two ways that cells make ATP?
Substrate-level phophorylation and chemiosmosis (majority made this way)
Where does chemiosmosis occur and what does it need?
Occurs in inner mitochondrial membrane, requires O2
What happens in substrate-level phosphorylation?
Direct transfer of phosphate group to ADP from another molecule (like phosphoenolpyruvate, or PEP)
Activation energy
Energy required to destabilize existing chemical bonds and start a chemical reaction
What do catalysts do?
Reduce activation energy and increase reaction rate (but not affect final equilibrium)
What do enzymes do?
Proteins that carry out most catalysis in cells (some done by ribozymes in RNA)
What is the reactant molecule of an enzyme?
Substrate - enzymes usually relatively specific in choice of reactant molecule
Where does substrate bind?
Active site
What conditions do enzymes need/prefer?
Optimum pH and temperature (where they function best); sometimes they need a coenzyme
When does an enzyme catalyzed reaction reach maximum rate?
When substrate concentration is high and all enzyme molecules are occupied with substrate molecules
Competitive inhibition
Competitive inhibitor binds to active site, preventing substrate from binding (reversible)
Uncompetitive inhibition
Uncompetitive inhibitor binds to enzyme-substrate complex, preventing release of products
Noncompetitive inhibition
Noncompetitive inhibitor binds at site other than active site, changing enzyme structure so that normal substrate binding is blocked
Allosteric regulation
Effector molecule binds to site other than active site of enzyme, inducing enzyme to change its shape
For multi-subunit allosteric enzymes, what does the reaction rate vs. substrate concentration graph look like?
Has sigmoidal kinetics (and are important sites of metabolic control): once substrate binds first active site, quaternary structure changes and other sites are more likely to bind substrate - rapid rxn rate increase
What is an example of an allosteric protein?
Hemoglobin (in the way it binds oxygen)
Irreversible inhibition
Inhibitor binds to certain side chains at active site of enzyme and permanently deactivates the enzyme
Allosteric regulation: what’s the difference between active and inactive form of enzyme?
Active form has proper shape for substrate binding; inactive form has shape that cannot bind substrate
