ENERGY AND METABOLISM (LECTURE 2) Flashcards
Define metabolism. (2)
It is the sum of all chemical reactions within an organism. These chemical reactions are organized into metabolic pathways.
Define metabolic pathways. (2)
A metabolic pathway is a chain of reactions. Enzymes catalyze every step in the metabolic pathway.
What are catabolic reactions? (2)
Catabolic reactions breakdown complex molecules into simpler compounds. These reactions release energy.
What are anabolic reactions? (2)
Anabolic reactions build complex molecules from simpler ones. These reactions consume energy.
What is the most significant example of a catabolic reaction?
Cellular respiration is a catabolic reaction.
What is the most significant example of an anabolic reaction?
Photosynthesis is an anabolic reaction.
What is energy coupling?
It is when a catabolic reaction is used to drive an anabolic reaction.
What is the first law of thermodynamics?
Energy is neither created nor destroyed (but it can be transformed).
What is the second law of thermodynamics?
Every energy transformation makes the universe more disordered (increases entropy), due to the inevitable loss of usable energy as heat.
What is Gibbs free energy (G)?
The portion of a system’s energy that is available for work.
What is the formula for Gibbs free energy (G)?
G = H - TS, where H is enthalpy (the total energy of the system; energy in chemical bonds), T is the temperature and S is the entropy (disorder in a system).
What are the formulas for the change in free energy (ΔG)? (2)
ΔG = G(products) - G(reactants) ΔG = ΔH - TΔS
What can the change in Gibbs free energy (ΔG) tell us about a reaction?
ΔG tells you whether a reaction is spontaneous or not.
(-)ΔG implies what? (4)
That the reaction is spontaneous and that energy is released. These reactions proceed alone and are exergonic (net release of energy).
(+)ΔG implies what? (3)
That the reaction is non-spontaneous. These require energy to proceed and are endergonic (net input of energy).
The change in free energy (ΔG) of photosynthesis is (+), meaning what? (3)
This means that photosynthesis is non-spontaneous, endergonic and the products have more free energy.
The change in free energy (ΔG) of cellular respiration is (-), meaning what? (3)
This means that cellular respiration is spontaneous, exergonic and the products have less free energy.
If a reaction is exergonic, what can we say about the reverse reaction?
The reverse reaction must be endergonic.
What can we say about a reaction when ΔG = 0? (3)
If ΔG = 0, that reaction is at equilibrium (forward and reverse reactions occur at the same rate) and the system cannot do any work.
Can a cell survive if it is at equilibrium (ΔG = 0)?
A cell at equilibrium cannot be alive.
What is metabolic disequilibrium? How does this apply to cells?
This is when products are displaced to be used as reactants for other metabolic pathways - cells are open systems; things are constantly added and removed.
Describe energy coupling using the terms: spontaneous, non-spontaneous, exergonic and endergonic.
Cells power endergonic (non-spontaneous) reactions using the energy released by exergonic (spontaneous) reactions.
Work in your body is ____, meaning it ____ energy.
Work in your body is endergonic, meaning it requires energy.
What are the 3 types of work that occur in the body? Provide an example for each.
Chemical (protein synthesis), mechanical (muscle contraction) and intracellular transport (active transport across the cell membrane).
What is ATP? (full name)
Adenosine triphosphate.
Describe the significance of the hydrolysis of ATP.
The hydrolysis of ATP (ATP –> ADP + Pi) is a highly exergonic reaction (the products are much more stable than the reactant). In our cells, ATP hydrolysis is coupled to the body’s endergonic processes.
What does Pi stand for and what is its chemical formula?
Pi stands for inorganic phosphate, H3PO4.
If the hydrolysis of ATP occurred in a test tube, what would happen?
The test tube would get hot.
What is the ATP cycle? (2)
ATP is renewable. Its synthesis requires energy, its hydrolysis yields energy.
If cellular respiration releases 686 kcal/mol (-ΔG) and ATP synthesis required 7.3 kcal/mol (+ΔG), then how many ATP molecules could we create per 1 glucose molecule? How many would actually be formed?
There is enough energy to form 94 ATP molecules, but only enough free energy to form 38 ATP molecules (60% of the energy released is lost as heat).
How is ATP hydrolysis coupled to chemical (synthesis) work? (not conceptually, on a molecular level)
ATP transfers a phosphate group to a reactant to “activate it”.
When is the phosphate group inorganic?
The phosphate group is considered inorganic (Pi) when alone. If it is attached to an ATP molecule or other, it is simply a phosphate group (denoted P).
How is ATP synthesis coupled to transport work (active transport)?
The transfer of a phosphate group onto a carrier protein causes a change in the conformation of the protein, allowing it to move a molecule across the membrane.
