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7 Mar 2018

10. The phosphofructokinase (PFK) enzyme is one of the key players in the glycolytic pathway in which glucose eventually breaks down into pyruvate, some ATP is generated, and some NAD+ is reduced. PFK catalyzes the committed step in the pathway and is under extensive regulation. Which of the following compounds would you expect to activate PFK? Explain why.

A. ADP

B. NADH

C. Pyruvate

D. ATP

E. All of the above

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7 Mar 2018

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Phosphofructokinase (PFK1) is a glycolytic enzyme that catalyzes the irreversible transfer of a phosphate from ATP to fructose -6-phosphate to form fructose-1, 6- bisphosphate.

fructose-6-phosphate + ATP --> fructose-1,6-bisphosphate + ADP

PFK1 is the key regulatory enzyme for glycolysis. When ATP levels are high in the cell, the cell no longer needs metabolic energy production to occur. In the case of these high energy levels, PFK1's activity is inhibited by allosteric regulation by ATP, which essentially closes the valve on the flow of carbohydrates through glycolysis.

Recall that allosteric regulators bind to a different site on the enzyme rather than the active (catalytic) site. ATP binds to the regulatory site and decreases PFK1 activity. ATP bound in the regulatory site acts as a modulator by lowering the affinity of PFK1 for its substrate, fructose-6-phosphate. AMP on the other hand, which is generated when the cell is in a low energy state binds to allosteric site and increases enzyme activity.

7. The enzyme PFK1 is an example of a non-regulatory enzyme or regulatory enzyme?

8. How is PFK regulated?

A. It is not regulated because it is a non-regulatory enzyme

B. allosteric enzyme regulation

C. covalent enzyme regulation

D. or proteolytic cleavage enzyme regulation?

9. What is the substrate and to which site on the enzyme does it bind? Which compounds are the positive and negative effectors?

10. In which conformational state would the enzyme be when negative inhibitors bind and in which conformational state would the enzyme be when positive inhibitors bind?

11. PFK1 is a heterotropic or homotropic regulatory enzyme?

12. Draw (or insert the picture from your course packet available on Canvas) the graph that corresponds to this reaction. Your graph should include the activity of PFK without bound effectors, with bound positive effector, and with bound negative effector. Label (or describe) each line to distinguish these along with which molecules are positive and negative effectors.

13. How does Vmax and K0.5 change with the positive and negative effectors?

1. Integrated metabolism

A. A molecule of glucose that you eat can eventually be transformed into part of a fatty acid that you store. Circle the pathways/cycles below that are part of this overall flow of carbon atoms. Cross out any that are not.

Gluconeogenesis, beta-oxidation, citric acid cycle, glycolysis, urea cycle, fatty acid synthesis

B. Trace the metabolic path of this glucose molecule through the enzymes it encounters along the way to being made into fat. Write all the enzymes in the list below into the proper places in the figure below. If the enzyme is not used, write its name in a ânot used" column. If it is used, write the enzyme in the order that the carbon atoms from glucose encounter the enzymes.

Pyruvate dehydrogenase, fumarase, aldolase, lactate dehydrogenase, pyruvate kinase, acetyl CoA carboxylase, fatty acid synthase, hexokinase, carnitine acyltransferase, ATP synthase

B. What is the minimum number of glucose molecules that would be necessary to be the carbon source for synthesis of a 16-carbon fatty acid through this pathway?

C. How many net glucose can be made from one molecule of a 16-carbon fatty acid?

2. Describe each cycle/transport system (compounds, compartments, tissues) and explain its purpose:

A. citrate transport system

B. Cori cycle

C. glucose/alanine cycle

Explain the logic of these pathway regulations:

A. Phosphofructokinase, not hexokinase, is the main regulation site of glycolysis.

B. SuccinylCoA inhibits the entry of acetyl CoA into the citric acid cycle.

C. NADH inhibits pyruvate dehydrogenase.

D. Citrate inhibits the citric acid cycle and activates acetyl-CoA carboxylase.

E. Insulin leads to activation of glycogen synthase.

ochrereindeer904

A catabolic pathway would predictably result in the
A) reduction of a sugar.
B) synthesis of a macromolecule.
C) breakdown of a macromolecule.
D) breakdown of an atom.
2.
The drug Ritonavir is used to treat people with HIV/AIDS. It worksby binding to the active site of HIV-1 protease, an enzyme used bythe AIDS virus to create new proteins for production of newviruses.Once bound, the HIV-1 protease cannot produce proteins.Ritonavir can be classified as a(n)
A) competitive inhibitor.
B) allosteric inhibitor.
C) activator.
D) non-competitive inhibitor.
3.
During cellular respiration, __________ is the final electronacceptor that allows the regeneration of the cellâs supply of NAD+.In fermentation, ____________ is the final electron acceptor forNAD+ regeneration.
A) pyruvate / lactic acid
B) pyruvate / oxygen
C) ethanol / CO2
D) oxygen / pyruvate
4.
Which of the following clues would tell you if a cell isprokaryotic or eukaryotic?
A) whether or not the cell carries out cellular metabolism
B) the presence or absence of ribosomes
C) whether or not the cell is partitioned by internalmembranes
D) whether or not the cell contains DNA
5.
Phosphofructokinase (PFK) is an allosteric enzyme that regulatesglycolysis. When cellular concentrations of ATP and citrate become__________, this enzymeâs activity decreases. When cellularconcentrations of AMP become ________, the enzyme isactivated.
A) high / high
B) high / low
C) low / high
D) low / low
6.
______________ is an enzyme that can utilize the free energy in thehydrogen gradient (voltage) produced between the inner and outermembrane of the mitochondrion. The enzyme uses this energy toproduce ________.
A) ATP synthase/ ATP
B) PFK/ ATP
C) PFK/ glucose
D) ATP synthase/ ADP
7.
ATP is able to do cellular work because it
A) has a high energy phosphate bond that can be hydrolyzed torelease energy.
B) converts light energy into chemical bond energy.
C) contains the sugar ribose, which can provide additional energyfor a cell.
D) its hydrolysis is endergonic.
8.
A solution of starch at room temperature does not readily decomposeto form a solution of simple sugars because
A) the starch solution has less free energy than the sugarsolution.
B) the activation energy barrier for this reaction cannot besurmounted.
C) the hydrolysis of starch to sugar is endergonic.
D) starch hydrolysis is nonspontaneous.
9.
A person exposed to toxins would have more activity in their___________compared to an unexposed person.
A) lysosomes
B) Golgi bodies
C) rough endoplasmic reticulum
D) smooth endoplasmic reticulum
10.
Which of the following statements about fermentation is true?
A) The function of fermentation is to regenerate the fermentingcells' supply of NAD+.
B) Fermentation allows a fermenting cell to gain more energy perglucose molecule than a non-fermenting cell.
C) Fermentation produces either lactic acid or ethanol that thefermenting cell can use as an energy source.
D) Fermentation is a universal process that occurs in all cells andall organisms.
11.
A glucose molecule is completely broken down to carbon dioxide andwater in glycolysis and the citric acid (Krebs) cycle, but togetherthese two processes yield only a few molecules of ATP. Whathappened to most of the energy that the cell obtains from theoxidation of glucose?
A) It was lost as heat.
B) It is stored in the carbon dioxide and water molecules releasedby these processes.
C) It is stored in the ATP that was formed by glycolysis and thecitric acid cycle.
D) It is stored in NADH and FADH2
12.
The First Law of Thermodynamics states that
A) entropy tends to increase in a system.
B) entropy tends to decrease in a system.
C) energy cannot be created nor destroyed.
D) the quality of energy in the universe is decreasing.
13.
The endosymbiotic theory states that _______________ evolved as aresult of a symbiotic relationship between different types ofbacteria. _____________ is thought to be the selective factor thatmade this symbiosis advantageous.
A) mitochondria / A change in the Earthâs atmosphere from anaerobicto aerobic
B) endoplasmic reticulum / A decrease in the amount of foodavailable in the environment
C) chloroplasts / A change in the Earthâs atmosphere from aerobicto anaerobic
D) lysosomes / A decrease in the amount of food available in theenvironment
14.
A mutation in a fruit fly affects one of the proteins that pumphydrogen ions across the inner mitochondrial membrane; thismutation makes that particular protein function less efficiently.When comparing aerobic cellular respiration in this fly with awild-type fly, you would predict that the mutant fly would
A) produce less ATP than a wild-type fly.
B) show no difference in ATP production when compared to awild-type fly.
C) produce more ATP than a wild-type fly.
D) not be able to produce any ATP via aerobic cellularrespiration.
15.
Proteins that are destined to be exported from the cell have unique_________________ that are recognized by signal recognitionparticles and thus moved to the _________________ duringtranslation.
A) phosphofructokinases / nucleus
B) codons / rough endoplasmic reticulum
C) signal recognition sequences / rough endoplasmic reticulum
D) signal recognition sequences / free ribosomes
16.
During the Krebs cycle
A) NADH is oxidized.
B) ATP is produced.
C) pyruvate is produced.
D) Acetly CoA gains a carbon to form pyruvate.
17.
Why does the oxidation of organic compounds by molecular oxygen toproduce CO2 and water release free energy?
A) Electrons are being moved from atoms that have a lower affinityfor electrons (such as C) to atoms with a higher affinity forelectrons (such as O).
B) The electrons have a higher potential energy when associatedwith water and CO2 than they do in organic compounds.
C) The covalent bond in O2 is unstable and easily broken byelectrons from organic molecules.
D) The covalent bonds in organic molecules and molecular oxygenhave more kinetic energy than the covalent bonds in water andcarbon dioxide.
18.
In a chemical reaction, if ?G is negative, it means that thereaction is
A) exergonic, and work needs to be done for the reaction toproceed.
B) exergonic, and work can be done with energy released from thereaction.
C) endergonic, and work needs to be done in order for the reactionto proceed.
D) endergonic, and work can be done with energy released from thereaction.
19.
The energy for an endergonic reaction comes from a(n) ___________reaction.
A) ADP + P --> ATP
B) endergonic.
C) exergonic.
D) anabolic
20.
Glycolysis
A) involves catabolic reactions and ATP is produced.
B) involves anabolic reactions and ATP is produced.
C) involves catabolic reactions and creates energy.
D) involves anabolic reactions and creates energy.