Quiz
Biol 334 continued
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Perguntas do quiz (44)
1For the reaction A -----> B, ΔGo' = -32 kJ/mol.
The reaction is started in water (in a test-tube) with 10 mmol of A & 0 mmol B. After 48 hours, chemical analysis revealed the presence of 8 mmol A, & 2 mmol B.
Which is the likely explanation?- AA and B have attained equilibrium concentrations
- BEquilibrium has not been reached since B formation is kinetically slow
- CThe result described is impossible, given that ΔGo' = - 32 kJ/mol
- DAn enzyme has shifted the equilibrium to A
- EFormation of B is thermodynamically unfavourable
2Which of the following statements is NOT correct
- AIf the Keq for a chemical reaction is much smaller than its mass action ratio then the forward reaction is favored.
- BNear-equilibrium enzymes catalyze reversible reactions.
- CThe more a reaction is displaced from equilibrium, the more negative its ΔG’ becomes
- DFor a reaction catalyzed by a ‘non-equilibrium’ enzyme, Keq will be far larger than the mass action ratio.
- ENon-equilibrium enzymes control flux through metabolic pathways.
3Acetyl-CoA hydrolase catalyzes the following reaction: acetyl-CoA + H20 → acetate + CoA.
A chemist is provided with the following information:
Oxaloacetate + acetyl-CoA + H20 → citrate + CoA ; ΔGo' = -32 kJ/mol
Oxaloacetate + acetate → citrate ; ΔGo' = -2 kJ/mol
From this information the biochemist concludes that the reaction catalyzed by acetyl-CoA hydrolase:- Ais at equilibrium in vivo.
- Bis displaced from equilibrium in vivo.
- Cis exothermic (or ‘exergonic’).
- Drequires an energy input in order to proceed in the forward (acetate producing) direction.
- Erequires an allosteric activator before it will occur in vivo.
4Complete the following sentence correctly. The majority of enzymes in a catabolic pathway…
- Acatalyze a reaction having a highly negative ΔG’
- Bcatalyze a reaction for which the equilibrium constant (Keq ) approximately equals the mass action ratio
- Cmarkedly lower the ΔGo’ for the reaction that they catalyze
- Dare allosteric ‘pacemaker’ enzymes
- Egenerate ATP via “substrate level phosphorylation”
5Under what special circumstance is the following equation the correct expression for the actual (in vivo) free-energy change of the reaction A -----> B?
G= = Go’ + RTlnKeq- AWhen the reaction is highly exothermic.
- BWhen the activation energy has been lowered
- CWhen the enthalpy of the reaction has been exceeded
- DWhen the reaction is greatly displaced from equilibrium in vivo
- EWhen the reaction is at equilibrium in vivo.
6The hydrolytic reaction: ATP + H20 ADP + Pi, has a standard free energy change, ΔGo’ = -30.5 kJ/mol
The actual (in vivo) free energy change for this reaction in healthy red blood cells = ΔG’ = -50 kJ/mol
What do these ΔGo’ &/or ΔG’ values tell us about ATP hydrolysis (to ADP + Pi)?- Athe reaction is close to equilibrium in the red blood cell
- Bthe equilibrium position for this reaction greatly favours the products, ADP + Pi
- Cthis reaction is greatly displaced from equilibrium in the red blood cell
- DA & B are both correct
- EB & C are both correct
7A new species of bacteria, Comparata biochemica, was discovered that catalyzes the following reaction:
Lactate Ethanol + CO2
Calculate the standard free energy change (ΔGo') for the above reaction, from the following information:
acetaldehyde + CO2 → pyruvate ΔGo’ = +19.8 kJ/mol
acetaldehyde + NADH + H+ → ethanol + NAD+ ΔGo’ = -23.7 kJ/mol
pyruvate + NADH + H+ → lactate + NAD+ ΔGo’ = -25.1 kJ/mol- A+18.4 kJ/mol
- B-48.8 kJ/mol
- C-18.4 kJ/mol
- D-68.6 kJ/mol
- E+3.9 kJ/mol
8The ΔGo' values for the 3 different reactions shown below are given:
1. Malate + NAD+ -----------> Oxaloacetate + NADH + H+ ΔG o' = +30 kJ/mol
2. Oxaloacetate + acetyl-CoA + H2O --------> Citrate + CoA ΔG o' = -32 kJ/mol
3. Oxaloacetate + acetate -----------> Citrate ΔG o'= -2 kJ/mol
What is the ΔG o' value for acetyl-CoA hydrolysis?
i.e., Acetyl-CoA + H2O ----> Acetate + CoA , ΔG o' = ???- A+30 kJ/mol
- B-34 kJ/mol
- C-62 kJ/mol
- D-30 kJ/mol
- ECan’t compute from information given
9The bacteria Pseudomonas. saccharophila contains sucrose phosphorylase, an enzyme that catalyzes the phosphorolytic cleavage of sucrose as follows: Sucrose + Pi -----------> Glucose-1-P + Fructose.
Calculate the standard free energy change (ΔGo') for the above reaction, from the following data.
1. H2O + Sucrose --------> Glucose + Fructose; ΔG o' = -7.0 kcal/mol
2. H2O + Glucose-1-phosphate --------> Glucose + Pi; ΔG o' = -5.0 kcal/mol.- A-12 kcal/mol
- B-2.0 kcal/mol
- C+2.0 kcal/mol
- D+12 kcal/mol
- Ecannot compute without additional information
10Which of the following statements concerning the "control analysis" approach to metabolic control is FALSE?
- Aa flux control coefficient of 0.8 suggests that this particular enzyme is relatively unimportant in controlling pathway flux
- Bits application does not require prior knowledge of which enzyme(s) in the pathway catalyze the "pacemaker" or "rate determining step" of the entire pathway.
- Cit predicts that pathway control is shared (to varying degrees) by all the enzymes of the pathway.
- Dit provides a way to quantify the relative contribution of each enzyme in a pathway to overall regulation of pathway flux in the intact system.
- Eit is based upon the fact that biological systems may display regulatory properties not possessed by the isolated components.
11Using an in vivo system, you wanted to identify the major sites of control for a metabolic pathway:
E1 E2 E3 E4 E5
A → B → C → D→ E → F
Using Metabolic Control Analysis, you determined the flux control coefficient for each enzyme in the pathway
Based on the data above, what could you conclude?
- AThis pathway does not have a rate-limiting step.
- BE2 is most likely the pacemaker enzyme for this pathway.
- CE3 and E5 are both pacemaker enzymes in this pathway
- DFlux control coefficients provide no information regarding pacemaker enzymes.
- EIn this pathway, flux is not controlled
12During mitochondrial respiration AND chloroplast photosynthesis…
- AATP is generated via active transport of H+ ions across a membrane by a H+-pumping ATPase
- BATP is converted into ADP and Pi via ‘chemiosmotic coupling’
- CAn electron transport chain transforms redox energy into proton motive force
- DATP is generated by oxidizing ‘fuel’ molecules
- EATP is generated via substrate level phosphorylation
13Which of the following statements concerning pyrophosphate (PPi) and adenylates is false?
- APPi has a lower standard free energy of hydrolysis than ATP.
- BIn some species PPi can be used in place of ATP for powering the active transport of protons across a membrane.
- CATP is believed to have evolved before PPi (for cellular energy transduction)
- DPPi has a phosphoanhydride bond, whereas AMP does not
- EThe ability to employ PPi as a substitute for ATP to power certain aspects of cellular 'work' may be a key adaptation that helps some species to survive environmental (abiotic) stress
14In the cytosol of plant cells, the pyrophosphate (PPi) produced as a byproduct of macromolecule synthesis…
- Ais used as an energy source for converting CO2 into starch
- Baccumulates owing to the absence of PPi-dependent active transport
- Ccan be used in place of ATP to provide energy for some aspects of ‘cellular work'
- Dcannot be used to power the active transport of protons (H+ ions) across a membrane
- Eis immediately hydrolyzed by inorganic pyrophosphatase
15In the cytosol of mammalian muscle cells, the pyrophosphate (PPi) produced as a byproduct of macromolecule synthesis:
- Ais used as an energy source to synthesize glycogen from glucose.
- Baccumulates owing to the absence of PPi-dependent active transport.
- Ccan be used in place of ATP to provide energy for some aspects of ‘cellular work’.
- Dis used to power the active transport of protons across a membrane.
- Eis immediately hydrolyzed by inorganic pyrophosphatase
16Biological oxidation-reduction reactions always involve
- Atransfer of electrons
- Btransfer of phosphates
- Cformation of water
- Dmitochondria or chloroplasts
- Edirect participation of oxygen
17Which of the following answers completes the sentence correctly? NAD+...
- Ais a flavin-adenine-dinucleotide
- Bis a product of the photosynthetic electron transport chain
- Cis the major acceptor used to transfer electrons from oxidative (catabolic) pathways to the mitochondrial electron transport chain for ATP production via oxidative phosphorylation
- Dis the major acceptor used to transfer electrons from oxidative reactions of catabolic pathways to reductive reactions of anabolic pathways
- Econtains a nicotinamide that donates a hydride ion during formation of NADPH
18Although AMP and NAD+ have very different metabolic roles, their chemical structures share the following components:
- Aan adenine base bonded to a nicotinamide group.
- Ba hexose sugar bonded to an adenine base.
- Ca phosphorylated deoxyribose sugar bonded to adenosine monophosphate
- Da ribose sugar bonded to a nicotinamide group.
- Ea ribose sugar bonded to an adenine base.
19In order to fly on a cool (e.g. 15oC) morning, bumblebees need to first increase the temperature of their flight muscle tissue to ~30oC. They do this by:
- Aallowing a futile cycle to occur between phosphofructokinase (PFK) and fructose-1,6-bisphosphatase (FBPase)
- B‘uncoupling’ their mitochondria (so that dissipation of the ‘proton motive force‘ creates heat rather than being coupled to ATP formation via ‘oxidative phosphorylation’)
- Cusing neighbouring ‘brown fat’ tissue to warm themselves (and their flight muscles) up
- Drunning around and rubbing their wings together so that they eventually warm up
- Eactivating luciferase to create light
20Carboxylase enzymes that replenish TCA (Krebs’) cycle intermediates that have been >drained= for biosynthesis are termed:
- Acatabolic
- Banabolic
- Camphibolic
- Danaplerotic
- Esecond messengers
21In healthy, rapidly growing, mammalian cells...
- ACatabolism is reductive, whereas anabolism is oxidative
- BOptimal cell growth requires that catabolism is minimal, but anabolism is maximal
- CFlux of metabolites through all metabolic pathways will occur at the fastest possible rate so that optimal growth can occur
- DThe carboxylation of pyruvate to oxaloacetate (catalyzed by pyruvate carboxylase) will likely occur at a rapid rate
- EMost metabolic enzymes will become activated by protein-kinase mediated phosphorylation
22Coarse’ metabolic control is not an efficient mechanism to control metabolism on a ‘moment-to-moment’ basis because:
- AProtein degradation uses up lots of ATP
- BThe level of mRNA encoding a particular protein always reflects the amount of the corresponding protein expressed in the living cell.
- CIt applies to enzymes of a pathway that catalyze freely reversible, ‘equilibrium’ type reactions
- DIt involves mechanisms that affect the activity of the pre-existing enzyme.
- EIt is too slow
23Which of the following statements is FALSE?
- AIncreased rates of transcription (mRNA production) from a specific gene always lead to a corresponding increase in the amount of the encoded protein
- BDetermining in vivo concentrations of substrate(s) and product(s) of enzyme catalyzed reactions helps to pinpoint metabolic reactions that are probably catalyzed by allosteric ‘pacemaker’ enzymes
- CIn a healthy cell most metabolic pathways have a relatively low overall energetic efficiency (of < 40%)
- DThe ‘bond energy’ of ATP can be transferred into other nucleoside triphosphates (e.g. deoxyATP, etc) owing to the action of nucleoside diphosphate kinase
- EE3 ligase catalyzes the covalent attachment of ubiquitin to a lysine residue of a target protein
24Allosteric’ mRNAs, whose 2o-structure is altered by binding of a specific metabolite (to inhibit translation) are known as:
- ARibosomes
- BRibonucleotides
- CRibozymes
- DRiboswitches
- ERiboflavonoids
25During biological ‘work’ some of a cell’s ATP pool is converted into ADP. AMP is an ‘amplifier’ of a small reduction in cellular [ATP] (and corresponding increase in [ADP]) owing to the action of:
- Anucleoside diphosphate kinase
- Badenylate kinase
- Cprotein kinase
- Dpyruvate kinase
- Ephosphoprotein phosphatase
26Several key pacemaker enzymes located in the chloroplast stroma that are involved in photosynthetic CO2 fixation (the ‘Calvin cycle’) are light activated. What specific type of post-translational control causes inactivation of these enzymes during the night (i.e. darkness)?
- Aprotein kinase-mediated phosphorylation
- Bthioredoxin-mediated reduction of a ‘disulfide bridge’ to a dithiol (-SH) group
- Cincreased stromal pHi from about pH 7.0 to pH 8.0
- Dmonoubiquitination by an E3 ligase
- Eoxidation of a dithiol (-SH) group to a disulfide (-S-S-) bridge
27Light-dependent alkalinization (increased pHi) of the chloroplast stroma promotes daytime activation of several Calvin cycle ‘pacemaker’ enzymes because these enzymes:
- Aare phosphorylated by a protein kinase that becomes much more active at higher pH
- Bbecome oxidized to their ‘active’ disulfide form at high pH
- Cbind allosteric activators in presence of low H+ concentrations
- Dhave a sharp alkaline pH-activity optima centred at about pH 8.0
- Eutilize atmospheric O2 to produce triose sugars
28If left unregulated, the combined reactions catalyzed by a protein kinase and a phosphoprotein phosphatase would theoretically:
- Aactivate anabolic pathways
- Blead to rapid conversion of glycogen to glucose-1-phosphate
- Ccause heat production owing to a ‘futile cycle
- Ddegrade cellular ‘second messengers
- Elead to maximal protein phosphoryation
29What prevents futile cycling between glycogen and glucose-1-phosphate in rapidly contracting skeletal muscle?
- AAMP allosterically inhibits glycogen phosphorylase while simultaneously activating glycogen synthetase
- Bglycogen phosphorylase is dephosphorylated whereas glycogen synthtetase is phosphorylated
- Cglycogen synthetase is quickly degraded to amino acids by contraction-inducible proteases
- Dprotein kinase-mediated phosphorylation of both glycogen phosphorylase and glycogen synthetase
- Ecalmodulin activates glycogen phosphorylase, whereas thioredoxin inhibits glycogen synthetase
30What mechanism of fine metabolic control causes acetyl-CoA carboxylase (ACCase) of mammalian cells to be converted from an inactive into a fully active form?
- Asubunit association due to reduced pH
- Bsubunit disassociation caused by reduced levels of its allosteric activator
- CACCase subunits associate when phosphorylated by cyclic-AMP dependent protein kinase
- Dan increase in the concentration of its allosteric activator (oleic acid)
- EACCase subunits associate when they are dephosphorylated by a protein phosphatase
31What type of fine control mechanism is believed to cause the conversion of the bifunctional pyruvate kinase (PK) of mammalian pituitary gland into a ‘thyroid hormone binding protein’?
- Areduced pHi
- Bphosphorylation of PK by cyclic-AMP dependent protein kinase
- Csubunit disassociation caused by reduced concentrations of fructose-1,6-bisphosphate (PK activator)
- Dan increase the concentration of PK’s substrate, phosphoenolpyruvate
- Ea reduction in the level of PK’s allosteric inhibitor, citrate
32The AMP-activated protein kinase (AMPK) is important because it:
- Aphosphorylates and thus inactivates key pacemaker enzymes of anabolism whenever an animal is subjected to a stress that depletes cellular ATP levels
- Bcouples extracellular signals (e.g. hormones) with intracellular control of key enzymes of carbohydrate metabolism
- Chelps the cell to synthesize more ‘fuel’ macromolecules like glycogen and storage lipids
- Dphosphorylates and thus activates phosphoenolpyruvate carboxykinase
- Ehas high activity when ATP levels are high
33Which of the following is not a correct statement about a metabolon?
- AA metabolon results in high flux.
- BThe active sites of the enzymes are in close proximity.
- CThe metabolon structure is irreversibly bound to a subcellular structure such as a membrane or the cytoskeleton.
- DA metabolon can protect against unstable intermediates.
- ECan prevent futile cycles from occurring
34Phosphoenolpyruvate carboxylase is a key pacemaker enzyme of plant cells that catalyzes the following reaction: phosphoenolpyruvate + HCO3- oxaloacetate + Pi
What type of metabolic pathway does phosphoenolpyruvate carboxylase function in?- Acatabolic
- Banabolic
- Cambiquitous
- Danaplerotic
- Ecyclic
35You are digesting a big meal and resting after playing an intense hockey game. Wha
- AAMP allosterically activates glycogen phosphorylase while simultaneously inhibiting glycogen synthetase
- Bglycogen phosphorylase is quickly degraded to amino acids by its polyubiquitination and subsequent proteolysis
- Cglycogen phosphorylase and glycogen synthetase are both dephosphorylated
- Dprotein kinase-mediated phosphorylation of both glycogen phosphorylase and glycogen synthetase
- Ecalmodulin inhibits glycogen phosphorylase while activating glycogen synthetase
36A multienzyme complex of enzymes that catalyze consecutive reactions in a metabolic pathway is known as a:
- Aholoenzyme
- Babiquiton
- Ckinome
- Dquaternary protein
- Emetabolon
37The following ‘metabolic map’ represents an amino acid anabolic pathway where H & J are different amino acid end-products, and A is a common precursor. E1 to E8 are different enzymes that catalyze the indicated reactions.
Suggest a sensible scheme for feedback allosteric control of specific enzyme(s) in this branched anabolic pathway.
- AF & I both inhibit E3, and C inhibits E1
- BH & J both inhibit E1
- CH inhibits E3, J inhibits E7
- DH inhibits E4, J inhibits E7, & D inhibits E1
- EH and J both inhibit E2
38When would protein kinase-mediated phosphorylation of glycogen phosphorylase and glycogen synthetase be promoted in your leg muscle cells?
- AWhen you are sprinting for an Olympic gold medal in the 100 meter event
- BWhen you collapse after running a 26 km ‘marathon’.
- CWhen you are sleeping
- DWhen you need to replenish your muscle cell’s store of ‘metabolic fuels’ such as glycogen
- EWhen you need to synthesize more triglycerides (fat stores).
39Which of the following statements is NOT correct:
- AIf the Keq is much smaller than the mass action ratio then the forward reaction is favored.
- BReactions that are close to equilibrium in vivo are freely reversible.
- CThe more a reaction is displaced from equilibrium, the more negative its ΔG’ becomes
- DNon-equilibrium reactions are those for which Keq is much larger than the corresponding mass action ratio.
- EEnzymes that catalyze ‘non-equilibrium’ reactions in vivo play an important role in ‘fine’ metabolic control.
40What was the first protein discovered to be regulated by reversible phosphorylation (resulted in a Nobel Prize award in Physiology & Medicine…)?
- Aphospholipase C
- Ba transcription factor
- Cglycogen phosphorylase
- Dphosphoenolpyruvate carboxylase
- Eglycogen synthetase
41Which of these statements about enzyme-catalyzed reactions is FALSE?
- AAlthough enzymes have no effect on a reaction’s standard free energy change (ΔGo'), they greatly influence its actual in vivo free energy change (ΔG').
- BKm = [substrate] at which Vo = (0.5 x Vmax).
- CIf enough substrate is added, Vmax can eventually be attained in the presence of a mixed competitive inhibitor.
- DEnzymes accelerate chemical reactions by lowering their activation energy.
- EA low Ki or I50 value indicates that its a relatively potent (strong) enzyme inhibitor
42In the cytosol of plant and animal cells, pyrophosphate (PPi) is produced as a byproduct of macromolecule synthesis. Which statement regarding pyrophosphate (PPi) is false?
- APPi and PPi-dependent enzymes help plants to survive unavoidable stresses that they are exposed to in their natural environment.
- BPPi accumulates in the plant cytosol owing to the absence of soluble inorganic pyrophosphatase
- CAnimals never use PPi in place of ATP to provide energy for some aspect of ‘cellular work’.
- DPlants can use PPi instead of ATP for powering the active transport of ions across a membrane
- EThe Keq for PPi hydrolysis (to 2Pi) is greater than the Keq for ATP hydrolysis (to ADP & Pi).
43Which of the following answers completes the sentence correctly?
NADP+...- Ais a flavin-adenine-dinucleotide
- Bis the major acceptor used to transfer electrons from oxidative reactions of catabolic pathways to reductive reactions of anabolic pathways
- Cis produced by the photosynthetic electron transport chain of illuminated chloroplasts.
- Dis the major acceptor used to transfer electrons from oxidative (catabolic) pathways to the mitochondrial electron transport chain for ATP production via oxidative phosphorylation.
- Econtains a nicotinamide group that donates a hydride ion during formation of NADH.
44Which of the following statements is FALSE ?
- ACertain neurodegenerative diseases such as Alzheimer’s have been linked to defective protein degradation
- BPhosphorylation can influence a protein’s activity, subcellular location, or interactions with other proteins
- CPhosphorylation of transcription factors influences gene expression.
- DThe cyclic-AMP dependent protein kinase is inhibited when its catalytic and regulatory subunits dissociate
- EExcessive cell phone use is believed to cause enhanced phosphorylation of some cellular proteins.
Informações
- Descrição
- Biology Quiz sobre Biol 334 continued, criado por Margaret MacMillan em 10-02-2019.
- Autor
- Margaret MacMillan
- Idioma
- English
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