BCH 330 Exam 1 Questions And Answers

BCH 330 Exam 1 r r r


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BCH 330 Exam 1 Questions And Answers


1. Assume that the acid-base dissociation constant (pKa) of pyruvic acid is r r r r r r r r r r


2.0. Using pH as the x axis and "number of protons removed (from pyruvic acid)"
r r r r r r r r r r r r r r r


as the y axis, draw the pH dependence curve for this equilibrium: -
r r r r r r r r r r r r


at pH 2, pH = pKa (50/50 distribution)
r r r r r r r


-pryuvic acid = associated/ protonated version r r r r r


-pyruvate = dissociated version / conjugate base r r r r r r


-pH+/- 1 : 90/10 r r r


-pH+/- 2 : 99/1 r r r


2. What is the pKa precisely in terms of concentrations of pyruvic acid, pyru-
r r r r r r r r r r r r


vate, and H+? What is the practical significance of the pKa?: -pKa: acid-
r r r r r r r r r r r r r


base dissociation constant
r r


-measures affinity of a proton for the conjugate base r r r r r r r r


-pKa = -log(Ka) r r


-Ka = [pyruvate][H+] / [pyruvic acid]
r r r r r


-Ka is the acid-base dissociation equilibrium
r r r r r


-at low pKa: higher concentration of pyruvate
r r r r r r


-at high pKa: higher concentration of pyruvic acid
r r r r r r r


-mass action: determines distributions of the two
r r r r r r


-mass action coefficient (Q): Q= [C'][D']/[A'][B']
r r r r r


3. How would one calculate the Gibbs free energy change (”G d) for dissociation fro
r r r r r r r r r r r r


m pyruvate using the pKa value? Show how you manipulated the relevant equati
r r r r r r r r r r r r


ons to determine ”G d. What is the numerical value of ”G d at 20 degrees C (include u
r r r r r r r r r r r r r r r r


nits)?: -”G d = -RTlnKa (define variables too)
r r r r r r


-when we know pKa, use: Ka = 10^-pKa r r r r r r r


-T = degrees C + 273.4K
r r r r r


-units for ”G d: J/mol r r r


4. Write out the Gibbs equation and define each of the terms. Explain what each
r r r r r r r r r r r r r r


of the terms represents in the context of the "hydrophobic effect". Explain the e
r r r r r r r r r r r r r


nthalpic and entropic energy contribution to the net free energy stabilization of
r r r r r r r r r r r r


globular protein structures at temperatures between approx-
r r r r r r


imately 10 and 50 degrees C.: -”G u = ”H u -T ”S u (define variable -
r r r r r r r r r r r r r r


H enthalpy, S entropy)
r r r r



1r/r20

, BCH 330 Exam 1
r r r


Studyronlineratrhttps://quizlet.com/_cp6bkq
-hydrophobic effect explains energies of protein folding
r r r r r r


-Folded state (Pf) <--> Unfolded state (Pu)
r r r r r r


- -”G u: favors unfolded
r r


- +”G u: favors folded
r r r


-hydrophobic effect is affected by the enthalpic factor (”H u) and the entropic factor (-
r r r r r r r r r r r r r


T”S )
-enthalpic factor favors folded state; changes are due to changed in bonding (cova-
r r r r r r r r r r r r




2r/r20

, BCH 330 Exam 1 r r r


Studyronlineratrhttps://quizlet.com/_cp6bkq
lent, ionic, hydrogen bonding, vdw) r r r r


-enthalpy of hydrogen bonds forces proteins to fold due to a hydrogen cage r r r r r r r r r r r r


-Chaotropes (urea & guandinium) disrupt cage & cause unfolding r r r r r r r r


-entropic factor favors unfolded state & is the change in the number of conformations
r r r r r r r r r r r r r


5. Explain why temperatures above about 60 degree C typically result in protein r r r r r r r r r r r r


denaturation.: -temperature impacts the entropic term (- r r r r r r


T”S u) of the Gibbs equation (”G u = ”H u -T”S u) r r r r r r r r


-at high temperatures, temperature factor becomes a large multiplier
r r r r r r r r


-
hydrophobic effect / enthalpic term is offset & results in a negative ”G u, causing proteins t r r r r r r r r r r r r r r r


o denature r


-in this denatured/ unfolded state, there are more configurations
r r r r r r r r


6. What is the "mass action coefficient" and how is it used to convert the standar
r r r r r r r r r r r r r r


d state free energy (”G *) to the actual value of ”G ? Provide the equation.-
r r r r r r r r r r r r r


:- r


mass action coefficient (Q) is used to convert standard state free energy (”G *) to actual fr
r r r r r r r r r r r r r r r


ee energy (”G ) r r


-accounts for poise of the reactants and products in equilibrium r r r r r r r r r


-aka the partition coefficient r r r


-can only use ”G * in stead state conditions (1 atm, 298.1 K, 1 M)
r r r r r r r r r r r r r


-”G = ”G * + RTlnQ r r r r


-Q = [C]^c[D]^d / [A]^a[B]^b
r r r r


-
Q = iÀCi,p / iÀC i r (p is product concentration, r is reactant concentration, Ci is concentration
r r r r r r r r r r r r r r r


of all components of i)
r r r r


7. Explain why one must make the relevant calculation of converting from r r r r r r r r r r


”G * to ”G to use ”G information to understand the energetic progression of,
r r r r r r r r r r r r


for example, the glycolysis pathway.: -
r r r r r


understand why glycolysis is energetically favorable r r r r r


-
reactions 1, 3, and 10 drive glycolysis (metabolically irreversible reactions bc they have l
r r r r r r r r r r r r r


arge -”G 's) r ase (all cat- r r


-metabolically irreversible reactions: hexokinase, PFK- r r r r


1, pyruvate kin alyzed by kinases)
r r r r r


-other reactions: near equilibrium r r r


-more efficient because less energy is used r r r r r r


-
easier for reverse process, gluconeogenesis, to occur bc 7/11 enzymes needed are the e
r r r r r r r r r r r r r


xact same as the ones for glycolysis r r r r r r


-thermodynamic linkage is required for only 3 reactions to drive the whole process r r r r r r r r r r r r

3r/r20