Test 3 Unit 3-Energy and Cellular Respiration Flashcards
What is the law of Thermodynamics and define all variables.
ΔG = ΔH - TΔS ΔG: Free energy, spontaneous reactions ΔH: Enthalpy, potential energy ΔS: Entropy, disorder T: Temperature
Explain how enthalpy (ΔH) works.
Transformations that absord energy (endothermic) result in the products having MORE potential energy. (+ΔH)
Transformations that release energy (exothermic) result in the products having LESS potential energy. (-ΔH)
*If you gain potential energy (+ΔH), reaction is NOT spontaneous.
Explain how enthropy (ΔS) works.
The measure of wheter a reaction gains disorder.
Gas > Liquid > Solid.
*Reactions that gain disorder (+ΔS) tend to be spontaneous.
Explain free energy (ΔG).
-ΔG = spontaneous (exergonic) \+ΔG = NOT spontaneous (endergonic)
Explain how exergonic and endergonic reactions relate to catabolic and anabolic reactions.
- Catabolic = energy released = exergonic = spontaneous
- Anabolic = energy required = endergonicc = not spontaneous
Why does ATP hydrolysis release free energy?
ATP hydrolysis releases free energy, so it is exergonic (spontaneous) because:
- decrease in potential energy
- increase in entropy
Why is there less potential energy in ADP than in ATP?
Because the loss of the terminal phosphate has decreased the electrical repulsion among the negatively charged oxygen atoms of the phosphate groups.
Explain how ATP hydrolysis can make other reactions spontaneous in the cell .
Through energy coupling: an endergonic reaction occurs by being coupled to an exergonic reaction. the energy is provided by the exergonic breakdown of ATP.
Explain the concept of activation energy for enzymes
For chemical reactions to occur, bonds need to be broken and this requires a small input of energy called ACTIVATION ENERGY. Enzymes can accelerate reactions by lowering the activation energy.
Explain how enzymes reduce the amount of activation energy required to start a reaction
Enzymes reduce the activation energy by inducing the transition state. The binding of substrate(s) to an active site results in the substrate’s acquiring the transition state conformation. Enzymes can:
- Bring reacting molecules together (reacting molecules can assume the transition state only when they collide)
- Charge interactions: expose the reactant to altered charges that promote catalysis
- Change the shape of a substrate into a conformation that mimics the transition state.
What is a cofactor?
A nonprotein group that binds very precisely to the enzyme. Cofactors are often metals, such as iron, copper, zinc, or manganese. The cofactor binds to the enzyme and activates it.
Give an example of an enzymatic cofactor.
ATP, vitamins (nonprotein groups), Retinal, Ascorbic acid, or vitamin C, is used as a cofactor in hydroxylases.
How can 1.substrate concentration 2.enzyme concentration 3.pH 4.temperature affect the rate of reaction?
- In the presence of excess substrate, the rate of catalysis is proportional to the amount of enzyme. At some point, it reaches a saturation level if the enzyme concentration is constant (↑ substrate = not so efficient!)
- As enzyme concentration increases, the rate of product formation increases. (↑ enzyme = very efficient!)
- An enzyme has an optimal pH at which it is most active
- An enzyme has an optimal temperature at which it is most active. Heat-sensitive enzymes can be activated/inhibited with temperature changes.
Explain how enzymes can be regulated through competitive and non competitive interactions
- Competitive regulation: the competitive inhibiter molecule competes with the substrate for the active site and the substrate is unable to bind when the inhibitor is bound to active site.
- Non-competitive (allosteric) regulation: Can be activation or inhibition
Explain how allosteric activation/inhibition works.
- Activation:
Enzyme binds to allosteric activator and converts it to a HIGH-affinity state = the substrate can bind. - Inhibition:
Enzyme binds to allosteric inhibitor and converts it to a LOW-affinity state = the substrate is released.
What is the difference in efficiency of aerobic and anaerobic pathways?
- Aerobic respiration: 1 glucose = 36-38 ATPS (MOST EFFICIENT!)
- Anaerobic respiration: 1 glucose = 2-36 ATPS
- Fermentation: 1 glucose = 2 ATPS
Why is anaerobic respiration and fermentation less efficient than aerobic?
Because it uses non-O2 compounds as electron acceptors which are less efficient because they are less electronegative than O2, so they have less affinity for electrons.
Fermentation is a back-up that uses organic compounds as electron acceptors.
Where and why in cellular respiration does fermentation occur?
Why? If oxygen is absent or in short supply
Where? In the cytosol. Pyruvate remains in the cytosol and is reduced using the NADH generated by glycolysis.
