cell bio chapter 9 Flashcards
1st law of thermodynamics
centers around the conservation of energy, stating that the total energy of
a system & its surroundings remains constant; energy can neither be created nor
destroyed, but can be converted from one form to another.
2nd law of thermodynamics
centers around the degree of disorder in a system (entropy, S), stating
that it increases over time
T/F: Cells intuitively appear to violate the 2nd law, as their molecules are more ordered
(lower entropy) than their precursors
true
which one is correct?
- a cell is not an isolated system, with changes in entropy within a cell will be
balanced by changes in its environment - the formation of a peptide bond releases energy in the form of heat,
which increases the thermal motion & degree of disorder of surrounding molecules - In order for biochemical reactions that lower entropy to occur, the heat released by
the reaction must be sufficient to generate a greater increase in entropy in the
surrounding.
Gibbs free energy (G).
The change in free energy (∆G) of a reaction combines the effects of changes in
enthalpy (the heat released or absorbed, ∆H) & entropy (the degree of resulting
disorder, ∆S) according to the following equation (where T is the absolute temperature):
∆G = ∆H - T ∆S
T/F: All spontaneous chemical reactions proceed in the energetically favorable direction,
accompanied by a decrease in free energy (∆G < 0)
true
T/F: The ∆G of a reaction is determined not only by the intrinsic properties of the
reactants & products, but also by their concentrations & other reaction conditions,
such as temperature
true
T/F: The standard free-energy change (fixed concentrations & pressure, ∆G°) is directly
related to its equilibrium position
true
what does this equation say?
A ↔ B
∆G = ∆G° + RT ln [B]/[A]
*R = gas constant
The standard free-energy change (fixed concentrations & pressure, ∆G°) is directly
related to its equilibrium position
when ∆G = 0, what happens?
At equilibrium, ∆G = 0 & the reaction does not proceed in either direction
what is k in this equation?
∆G° = -RT ln K
The equilibrium constant for the reaction, (K = [B]/[A])
T/F:
* If the actual ratio [B]/[A] is greater than the equilibrium ratio (K), ∆G will be > 0 & the
reaction will proceed in the reverse direction (i.e. B → A)
* If the ratio [B]/[A] is less than K, ∆G will be < 0 & the reaction will proceed in the
forward direction (i.e. A → B).
true
T/F : Many biological reactions are thermodynamically unfavorable (∆G > 0) under cellular
conditions & require an additional source of energy
true
Adenosine 5’-triphosphate (ATP)
plays a central role in the process of unfavorable reactions by acting as a store of free energy within the cell, where the phosphodiester bonds in its phosphate
groups are high energy because their hydrolysis is accompanied by a relatively large
decrease in ∆G
glycolysis
- breakdown of glucose, initial stage in the breakdown of glucose & occurs in the absence of oxygen
- complete oxidative breakdown of
glucose yields a large amount of free energy - To harness the free energy in usable form, glucose is oxidised within cells in a series of steps coupled to the synthesis of ATP
- provides all metabolic
energy in anaerobic organisms,
however it is only the first stage of
glucose degradation in aerobic cells
T/F: In addition to producing ATP, glycolysis converts 2 molecules of NAD+ to NADH, in
which NAD+ acts as an oxidizing agent that accepts electrons from glyceraldehyde-3-
phosphate.
true
what does NADH do?
The NADH formed as a product must be recycled by serving as a donor of electrons
for other oxidation-reduction reactions within the cell. In anaerobic conditions, the NADH formed during glycolysis is reoxidised to NAD+ by
the conversion of pyruvate to lactate or ethanol.
what is the role of NADH in aerobic organisms?
the NADH serves as an additional source of energy by
donating its electrons to the electron transport chain, where they are ultimately used
to reduce O2 to H2O, coupled with the generation of additional ATP.
The citric acid Cycle
serves as the mitochondrial hub for the final steps in carbon skeleton oxidative catabolism for carbohydrates, amino acids, and fatty acids.
