Biochemistry Practice Problems IV with Answers

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1. Concerning hemoglobin, which of the following is correct?
a. Binds oxygen at a higher P50 value in “deep” or distal tissues
b. Binds oxygen best in the ferric oxidation state of heme
c. Carries carbon dioxide attached to ferrous iron heme groups
d. Shows Michaelis-Menton type kinetics using a Hill plot analysis

2. Periodic laboratory monitoring of Hemoglobin A1C has proven useful in assessing the success of chronic therapy of which primary disease state?
a. Hypertension
b. Diabetes Mellitus
c. Coronary artery disease
d. Lung cancer

3. Which of the following is a key part of the explanation of why the presence of fetal hemoglobin (HbF) is of benefit to the developing fetus?
a. HbF does not bind 2,3 BPG
b. HbF binds CO2 to a greater degree
c. HbF has a Hill plot with slope >1
d. HbF does not show heterotropic allosterism

4. Explain the potentially helpful function of myoglobin, given a low level of oxygenation of the deep or distal tissues due to poor blood circulation in a patient with failing heart function.
a. myoglobin offloads its O2 to hemoglobin, allowing hemoglobin to better oxygenate
tissues and thus help alleviate the falling pO2 in the diseased patient
b. myoglobin accepts more O2 and binds it tightly, which allows hemoglobin to bind
CO2 and carry it to the lungs for expiration
c. myoglobin does not play a role in states of low oxygenation, because of its sigmoidal
shaped dissociation curve, it typically acts most effectively at relatively high PO2 levels
d. myoglobin acts on some occasions as a reservoir of O2, since at rest it is essentially fully saturated; thus at times of low blood perfusion and resulting low oxygenation, myoglobin can help by substituting for hemoglobin as a secondary source of oxygen, and offload O2 at the tissue level

5. T-state hemoblobin has which of the following characteristics?
a. more O2 affinity with less release of O2 to tissues
b. less ionic bonds that hold the subunits in relation to each other
c. shorter bond length of Fe – O2 with resultant lower P50
d. generally lower percent of O2 saturation vs. R state

6. An explanation for the effect of lower pH levels on O2 affinity for hemoglobin includes:
a. shift in equilibrium toward more ionized carboxylate groups on Hb protein chains
b. decrease in [H+] causes increased levels of CO2, which increases O2 affinity
c. relatively higher levels of “conjugate base” groups on hemoglobin’s protein chains
d. shift in equilibrium toward more ionized amine groups on Hb protein chains

7. Which of the following is correct regarding the action of 2,3-BPG on hemoblobin?
a. in arterial blood, pO2 is about 30mmHg and normal levels of 2,3-BPG causes
hemoglobin to bind oxygen with more affinity in the lungs, and thus deliver a greater
amount of O2 to tissues where pO2 falls to near zero
b. 2,3-BPG effects are long-term in nature, since it requires a few weeks to up-regulate
production of this molecule
c. in the absence of 2,3-BPG, hemoglobin passing through the tissues would unload less O2, since the O2 dissociation curve would be shifted to the left
d. the observed shift in the O2 dissociation curve produced by 2,3-BPG would predict
that for any given pO2 level, the O2 saturation of hemoglobin is greater in the presence
of 2,3-BPG than that expected in its absence

8. Consider the half-reaction A to B with ΔGo’ of -7.0 Kcal/mol. We can couple this reaction successfully with another half-reaction X to Y with a ΔGo’ of +12.3 Kcal/mol. What is the ΔGo’ of the combined reaction Y + B → X + A ?
a. -19.3
b. – 5.3
c. +5.3
d. +19.3

9. A reaction at equilibrium has a ΔG of:
a. -2.303
b. Log of [Reactants] / [Products]
c. Zero
d. 1.4 Kcal/mol

10. Consider the half-reaction A + 2e- → B with Eo’ of +0.82 volts, which we desire to couple with the half-reaction C + 2e- → D with Eo’ of -0.32 volts. Using the coupled redox reaction that would yield B as a reduced product, calculate ΔGo’ for the combined reaction. Note: the Gas Constant, R=1.987 cal/mol-deg, Faraday’s Constant, F= 23.1 Kcal/mol. Use the formula: ΔGo’= -nFΔEo’.
a. +1.14
b. – 1.14
c. – 26.3
d. – 52.7

11. The specific portion or component of the NADH molecule that donates or accepts electrons in the cycling that occurs during redox reactions is:
a. riboflavin
b. adenine
c. nicotinamide
d. ribose

12. Which of the following correctly describes a ribozyme, and differentiates it from an
enzyme?
a. does not take on a tertiary structure in its final folded form
b. does not typically catalyze conversion to significant amount of product
c. differs in type of components making up the primary structure
d. exists in a proribozyme, precursor form until activation occurs