Biology Exam 2 Practice Questions
One way to generate acetyl-CoA is to convert pyruvate into acetyl-CoA by stripping off a CO2 molecule. The removal of CO2 is referred to as what type of reaction?
Decarboxylation
A new antibiotic has been developed. It acts as a noncompetitive inhibitor of an enzyme. How will this antibiotic affect delta G for the reaction that is catalyzed by the enzyme?
Delta G will be unaffected
A cell membrane is more permeable to K+ than Na+. What would happen if the membrane was more permeable to Na+ than to K+?
Due to the increased movement of Na+ inward, the membrane potential would become more positive.
What is the net number of ATP generated directly during glycolysis per molecule of glucose?
2
Arrange the electron acceptors in order from highest to lowest energy. 1 = Cytochrome C 2 = Oxygen 3 = Cytochrome C oxidase
1, 3, 2
How many ATP molecules are needed to transport 36 Na+ and 24 K+ across the membrane?
12
What are the products of one turn of the Citric acid cycle?
2 CO2, 3 NADH, 1 FADH2, 1 ATP
Why is formation of ATP by ATP synthase in the mitochondria known as oxidative phosphorylation?
A proton gradient created by the redox reactions of the electron transport chain is used to drive the synthesis of ATP.
When substrate-level phosphorylation occurs, it means that:
ADP is converted into ATP by the addition of a phosphate group.
How and where is ATP made in a eukaryotic cell?
ATP can be made by direct phosphorylation of ADP in the cytoplasm, and by an enzyme complex that uses the energy from a proton gradient to drive ATP synthesis in the mitochondria. It can also be made in other locations in the cell, depending on the cell type.
Why is the energy generated from the catabolism of sugars and other macromolecules ultimately harnessed to generate ATP?
ATP can be used by cells to drive endergonic reactions
If the inner mitochondrial membrane was freely permeable to protons (H+) what would be the most devastating result to the cell?
ATP would not be produced by oxidative phosphorylation.
What molecule can oxidize NADH?
Acetaldehyde
What important metabolic intermediate does not cross the inner membrane of the mitochondria?
Acetyl-COa
Glucose is not our only food source, nor the only one we can utilize in our bodies to generate energy. Other primary sources of energy include other sugars, proteins, and fats.What metabolic intermediate are fats primarily converted into?
Acetyl-CoA
When a person is in a state of fear, the hormone epinephrine is released. This hormone stimulates the activation of energy-generating catabolic pathways in order to provide the body with enough energy to respond to the element that is inducing the fear. How would that be helpful to a person who unexpectedly finds themselves in close proximity to a lion?
Activation of catabolic pathways would generate ATP. Breaking the bonds that connect one phosphate group to another in ATP could release energy that would allow that person to run and possibly escape the lion.
A human cell has a mutation in the gene that encodes the enzyme that generates lactate from pyruvate, rendering that enzyme completely non-functional. Assuming that there is ample glucose present, how would this cell generate energy in the presence of oxygen?
Aerobic respiration
Phosphofructokinase (PFK) is an enzyme that converts fructose 6-phosphate to fructose 1,6-bisphosphate, by adding a phosphate group. This is the first committed step of the metabolic pathway of glycolysis, and thus it is very tightly regulated. AMP binds to PFK at a site distinct from the binding site for fructose 6-phosphate, and stimulates the formation of fructose 1,6-bisphosphate. ATP binds to PFK at a site distinct from the binding site for fructose 6-phosphate, and inhibits the formation of fructose 1,6-bisphosphate. There are other regulators of this enzyme as well. What is the role of AMP in this example?
Allosteric activator
Many of the antiviral drugs currently used to treat HIV/AIDS also interfere with an enzyme that helps mitochondria multiply. Treatment can therefore result in a decrease in the number of mitochondria found in certain tissues. Given this information, what might you expect to see in patients treated with antiviral drugs?
An increase in lactic acid levels
Tetrodotoxin is a potent poison, produced by some newts, pufferfish, and blue-ringed octopus that affects sodium transport involved with the voltage gates in neurons. A friend swimming in the Caribbean is pricked by a pufferfish and gets very sick. The most likely action the poison takes is
Blocking an antiporter so sodium cannot rush in.
AMP-activated protein kinase (AMPK) is an enzyme that is activated by high levels of AMP in cells. If levels of AMP are high in cells, that means that levels of ATP are low. Once active, AMPK activates catabolic pathways and inhibits anabolic pathways in the cell. Why do you think that is the case? Choose the answer that best explains the role of AMPK.
By activating catabolic pathways, AMPK provides a mechanism to activate exergonic pathways, which is important if AMP levels are high in the cell.
Chronic Myelogenous Leukemia (CML) is a type of cancer that is caused by a specific chromosomal alteration that leads to the inappropriate expression of a kinase called Abl. Kinases are enzymes that put phosphate groups onto macromolecules such as proteins. A drug used to treat CML, imatinib, binds to the active site of Abl kinase. Why does this drug work to treat this type of cancer?
By binding to the active site, the drug prevents the ability of Abl kinase to bind to its substrate.
How do electrons enter the electron transport chain?
By the oxidation of NADH
The drug will move into the blood, through diffusion, for a long period of time, maintaining a constant concentration of drug in the blood.
Endocytosis
When taking oral medications, several nonpolar lipid cell membrane barriers will have to be passed before the polar drug can reach circulation. What is the likely method of transport mechanism the drug would use to cross the membrane? rev: 09_25_2019_QC_CS-182258
Facilitated diffusion
Your friend is having difficulty keeping track of the energy flow from glucose through glycolysis, the Citric acid cycle and electron transport. Your best advice would be to
Follow the electrons
What aspect of cellular respiration occurs in the cytoplasm in eukaryotic cells?
Glycolysis
When oxygen is unavailable during heavy exercise what process do muscle cells use for energy generation?
Glycolysis coupled with lactate fermentation
When cells possess plentiful amounts of ATP, what happens to cellular respiration processes within the cell?
Glycolysis is slowed.
If citrate levels are high in the cell, but ATP levels are low, what do you think will happen in the cell?
Glycolysis will be inhibited, but the Citric acid cycle will be functional, allowing it to be utilized to breakdown acetyl-CoA generated from beta-oxidation.
The production of phagolysosomes depends directly on which organelle?
Golgi apparatus
Phosphofructokinase is regulated by a number of factors, including high levels of ATP. Why is this enzyme regulated by ATP levels?
If ATP levels are high, it is important to directly inhibit the reaction that commits the substrate to glycolysis to allow the substrate to be available for other reactions, since the cell has ample energy.
While conducting an experiment, you realize that a competitive inhibitor was interfering with your reaction. How could you overcome this problem?
Increase the concentration of the correct substrate in the reaction.
In the reaction catalyzed by aconitase, the conversion of citrate to isocitrate is inhibited by fluoroacetate. Fluoroacetate is used as a pesticide. Why is this an effective pesticide?
It inhibits the Citric acid cycle
In order to lose weight and reduce body fat, a friend of yours has decided to eliminate all fat from his diet, while consuming unrestricted amounts of carbohydrates. What do you think of this idea?
It is a bad idea, because if ATP levels are high in cells, excess acetyl-CoA from the metabolism of carbohydrates can be used for fatty acid synthesis.
What happens to the oxygen that is used in cellular respiration?
It is reduced to form water
A novice gardener notices that many plants in his garden look wilted. What osmotic solution would you suggest the novice gardener use to best return the plants to full health?
Place the plants in a 5% solute solution so water can diffuse into the plant cells.
If dehydrogenation reactions were not possible and cells could only carry out basic redox reactions, how would this affect the ability of cells to harness energy from the breakdown of carbohydrates?
It would likely take more steps to breakdown carbohydrates to generate energy, as only one electron at a time could be removed.
The digestive organelle in cells requires a pump to move H+ against its concentration gradient to maintain an acidic environment. Based on this information, determine which group of terms can be used to explain this to a classmate.
Lysosome, uniport, active transport
Kinases are enzymes that can phosphorylate (transfer phosphate groups onto) macromolecules such as proteins. A particular kinase, Kinase 1 is known to promote cell division. It promotes cell division by phosphorylating Protein X. Phosphorylation of Protein X activates Protein X. Once activated, Protein X stimulates the production of other proteins such as Protein Y and Z that directly promote cell division. In order to function, Kinase 1 requires the presence of Metal A. However, in the presence of Protein A, Kinase 1 is nonfunctional. From the description, what is considered a cofactor of Kinase 1?
Metal A
Pyruvate oxidation in eukaryotic cells occurs in the ________.
Mitochondria
What would be the outcome if an increase in both intracellular sodium ion levels and extracellular potassium ion levels were to occur?
Multiple Choice The Na-K pump would accelerate because it needs to restore the membrane's resting concentration gradients.
Regardless of the electron or hydrogen acceptor used, one of the products of fermentation is always
NAD+
What is the oxidized form of the most common electron carrier that is needed for both glycolysis and the Citric acid cycle?
NAD+
What oxidizing agent is used to temporarily store high energy electrons harvested from glucose molecules in a series of gradual steps in the cytoplasm?
NAD+
Tacrolimus (FK-506) is a drug that inhibits an enzyme called calcineurin. Calcineurin is a protein phosphatase. This is an enzyme that dephosphorylates (removes phosphate groups) from proteins. When added to cells, tacrolimus can inhibit the dephosphorylation of a protein called NFAT, but it cannot prevent the dephosphorylation of a protein called CDK1. What is the most likely explanation for this finding?
NFAT is a substrate of calcineurin, but CDK1 is not
Many types of cancer cells have been detected to secrete significant levels of lactate. Do you think these cells are likely undergoing beta-oxidation?
No, because if lactate is being produced, the cell is not likely making use of the pathways needed to make use of the products of beta-oxidation.
You eat a bowl of beans as part of your dinner. As you digest the beans, the proteins that are present get broken down to their component amino acids. As your body destroys the macromolecules that were present in the beans, is the energy present in those molecules destroyed?
No. The energy contained within these macromolecules is converted into other forms of chemical energy and kinetic energy, though some is lost as heat.
When amino acids are degraded in cells, into what intermediate(s) of the aerobic respiration process are the carbon skeletons of amino acids primarily converted?
Pyruvate and Citric acid cycle intermediates
Matt is studying how the protein transferrin enters cells. He examines cells that have taken up transferrin, and finds clathrin-coated vesicles. What mechanism was used to take transferrin into the cell?
Receptor-mediator endocytosis
You decide to go on vacation in the mountains, where you are staying in a cabin. Unfortunately, when you turn on the water in the cabin you smell hydrogen sulfide (H2S) gas. After some research, you find out that the H2S may be due to the presence of sulfur bacteria living in your pipes. What molecule do these bacteria use as an electron acceptor?
SO4
Why must the electron transport chain proteins and molecules be embedded in a membrane?
So that protons can be compartmentalized and form a gradient
A biochemist wants to control the initial substrate-level phosphorylation that occurs in the tracheal cells of grasshoppers once glucose has crossed the plasma membrane. He has access to the following inhibitors: Rotenone - an electron transport chain inhibitor, Oligomycin - an ATP synthase inhibitor, and TLN-232, an inhibitor of glycolysis. Which inhibitor should he use to slow down initial substrate-level phosphorylation that occurs once glucose has crossed the plasma membrane?
TLN-232
in individuals with normal blood sugar levels, glucose is reabsorbed into the bloodstream in the kidney by members of the GLUT transporter family, which form an aqueous pore across the membrane through which glucose can move passively. As a result, no glucose is excreted in urine. However, in people with untreated diabetes mellitus, blood sugar levels are high and glucose is often present in the urine. What can explain this occurrence?
The GLUT transporters become saturated, allowing untransported glucose to be excreted in urine.
As a forensic pathologist, you have just completed an autopsy of a poisoning victim. After a thorough examination, you conclude that the victim died of cyanide poisoning. You know that cyanide binds to the cytochrome oxidase complex, and therefore list the official cause of death as suffocation due to cyanide exposure. However, if you wanted to provide a more technical explanation as to the cause of death, which process was specifically inhibited directly by cyanide?
The formation of water from oxygen
If ATP synthase had a mutation in the F1 complex portion of the protein, which function of ATP synthase would most likely be affected?
The conversion of ADP and Pi to ATP
Certain microbes release toxins that prevent ATP formation in phagocytes. Why would this be an effective defense?
The depletion of ATP decreases the energy available to the phagocyte, preventing phagocytosis.
Aerobic respiration involves the transfer of many electrons from glucose to electron carriers such as NAD+ over a series of multiple steps. Ultimately though, it is the reaction of glucose with oxygen to generate carbon dioxide, water and energy. Why doesn't glucose react directly with oxygen in cells?
The direct reaction of oxygen with glucose would be extremely destructive to cells.
Transdermal drug patches, such as nicotine patches, are applied to the skin. The drug is applied in a relatively high dosage to the inside of the patch, which is worn on the skin for periods of time. The drugs enter the bloodstream directly through the skin. Theoretically, how do the patches work?
The drug will move into the blood, through diffusion, for a long period of time, maintaining a constant concentration of drug in the blood.
Cytochromes contain a heme group similar to that in hemoglobin. The iron atom (Fe) in the center of the group can be oxidized and reduced. If someone was suffering from iron deficiency anemia, what stage of cellular respiration would be most affected?
The electron transport chain
As electrons move along the electron transport chain, they lose potential energy. How is the energy that is released used by the cell?
The energy is used to transport protons against their concentration gradient
Arsenic poisoning can lead to organ failure and death. Though arsenic can inhibit or interfere with a number of cellular enzymes, arsenic poisoning is thought to be mainly due to indirect inhibition of enzymes involved in both pyruvate oxidation and the Citric acid cycle. As a result, this compound must be able to enter which cellular compartment?
The mitochondrial matrix
A current problem in modern medicine is the development of drug resistance mutations. This occurs when a mutation arises in a disease-causing microbe making it resistant to a drug and thus rendering the drug useless in treating a specific disease. Many useful drugs are competitive inhibitors of specific enzymes, and the drug-resistance mutations prevent the binding of the drug. These types of mutations, in addition to preventing competitive inhibitor binding, can also sometimes reduce the activity of the enzyme. Why is that the case?
These mutations most likely change the shape of the active site of the enzyme
What is common to all of the oxidation reactions in the Citric acid cycle?
They are all characterized by a loss of electrons from an organic molecule coupled to the reduction of an electron acceptor.
What must happen to amino acids before they can be used in catabolic reactions?
They must be deaminated
Red blood cells do not contain mitochondria. How do red blood cells generate most of their ATP?
Through glycolysis coupled with lactic acid fermentation
Why are the components of the electron transport chain embedded in the inner mitochondrial membrane rather than floating freely in the cytoplasm of mitochondrial matrix?
To generate and maintain the proton gradient essential for ATP production.
2,4-Dinitrophenol (DNP) is a drug that can shuttle protons across biological membranes. In the 1930's it was used as a diet pill. Do you think this drug was effective in helping people to lose weight?
Yes, by moving protons directly across membranes, this drug disrupted the proton gradient needed to make ATP. Because ATP production is disrupted, the body will attempt to compensate by breaking down more fuels, such as fat.
In the absence of oxygen, can cells utilize the electron transport chain?
Yes, in the case that a cell can use a terminal electron acceptor other than oxygen, it can make use of the electron transport chain.
Does ADP contain the capacity to provide energy for the cell?
Yes. Cleaving the bond between the terminal phosphate and the phosphate attached to the ribose sugar can provide energy for the cell.
The Citric acid cycle occurs in the mitochondria. There are nine biochemical reactions involved in the Citric acid cycle, and they are highly ordered. Select the correct order. (Note: These are abbreviated and do not show NAD, ADP, ATP, or FAD.)
acetyl-CoA joins the Citric acid cycle and unites with oxaloacetate →forming citrate →which forms alpha-ketoglutarate → which forms succinyl-CoA → which forms succinate → which forms fumarate → which forms malate → which forms oxaloacetate
The energy needed to destabilize existing chemical bonds and start a chemical reaction is called
activation energy
The term oxidation is derived from the name of the element oxygen. This is reasonable, because oxygen
attracts electrons very strongly.
The organic nonprotein components that aid in enzyme functioning are called
coenzymes
The inorganic nonprotein components that participate in enzyme catalysis are known as
cofactors
A molecule that closely resembles the shape of a substrate for an enzyme and that decreases the activity of the enzyme would most likely serve as a(n)
competitive inhibitor
If Na+ levels were depleted in the extracellular fluid, rate of glucose movement would
decrease
To form NADH from NAD+, two electrons and a proton are removed from an organic molecule. What term best describes the reaction in which electrons and a proton are removed from an organic molecule?
dehydrogenation
Some single-celled protists, such as paramecia, live in an extremely hypotonic environment and have contractile vacuoles that
discharge excess water that has moved into the cell.
GABA receptors play an essential role in neurotransmission in the central nervous system. In response to the appropriate signal, these receptors open up and allow Cl- to flow into the cell. Given this information, GABA receptors can be classified as a
gated ion channel.
It is thought that the oldest stage of cellular respiration from an evolutionary perspective is
glycolysis
This process is common to all living cells:
glycolysis
What stage of cellular respiration can occur in human cells with or without oxygen present?
glycolysis
The electron transport chain in bacteria is located
in the cell membrane.
The energy released in the mitochondrial electron transport chain is used to transport protons into the
intermembrane space of the mitochondria.
Glucose is broken down through cellular respiration, which involves a large number of chemical reactions. At the end of the cellular respiration process, a large number of ATP molecules are generated, but yet, not all of the possible energy that is contained in a molecule of glucose can be harnessed through these chemical reactions to generate ATP. In other words, during cellular respiration, not all of the energy that is contained in a molecule of glucose is converted into the energy stored in ATP. What happens to the remaining energy?
it is lost as heat
E. coli uses lactose permease to transport lactose into its cell against its concentration gradient. The most likely reason is
lactose permease is a symport, and the high H+ (proton) concentration helps drive the movement of molecules across a cell.
Sea water is approximately 3% salt. Sea water is hypertonic to tissues of freshwater fish. Their tissues contain
less than 3% salt.
The formation of ATP as a result of the activity of the electron transport system is termed substrate-level phosphorylation
potential energy
Kinases are enzymes that can phosphorylate (transfer phosphate groups onto) macromolecules such as proteins. A particular kinase, Kinase 1 is known to promote cell division. It promotes cell division by phosphorylating Protein X. Phosphorylation of Protein X activates Protein X. Once activated, Protein X stimulates the production of other proteins such as Protein Y and Z that directly promote cell division. In order to function, Kinase 1 requires the presence of Metal A. However, in the presence of Protein A, Kinase 1 is nonfunctional. From the description, what is considered the substrate of Kinase 1?
protein x
In order to reuse an enzyme after the conclusion of an enzyme catalyzed reaction, what must occur?
the enzyme has to separate itself from the product
If the ΔG of a reaction was -31.45 kJoules, you would know that:
the reaction is spontaneous.
You return home to find that your baby brother has scattered his toy trains and trucks all over the floor of your room. As you begin to pick up the toys and put them away, you realize that even though he is just a baby, he has clearly mastered:
the second law of thermodynamics.
