BIO 327 Exam 3
Antimycin A is a piscicide (fish poison) used to manage fisheries and kill invasive species. Antimycin A blocks the transfer of electrons through the cytochrome b-c1 complex. What components of the electron transport chain are bound to high-energy electrons after treating a mitochondrion with antimycin A?
NADH and the NADH dehydrogenase complex are bound to high-energy electrons while O2 and the cytochrome c oxidase complex are not.
During the activation of a neuron, the action potential propagates in only one direction. How is this achieved in the neuron?
The Na+ channel becomes inactivated and refractory to reopening for a short time after the action potential passes.
Tetrodotoxin is a potent toxin found in a variety of organisms including the pufferfish. The toxin binds to the extracellular side of the Na+ channel and prevents channel opening. This leads to paralysis of muscles, including the diaphragm. Death from respiratory failure can occur after ingestion of as little as 1 mg of the toxin. Why does this toxin cause paralysis?
The membrane depolarization is not amplified along the axon.
Which of the following statements correctly describes the location of the photosystem I (PSI), photosystem II (PSII), and ATP synthase complexes used in photosynthesis?
PSI and ATP synthase are in the stroma thylakoids and grana end membranes, and PSII is in the grana thylakoid.
During photosynthesis, what happens in the water-splitting step?
It generates essentially all of the O2 in the Earth's atmosphere.
What is true of stage 2 of photosynthesis?
It produces glyceraldehyde 3-phosphate in the stroma.
Under what condition will a target cell always respond quickly to an extracellular signal?
The response does not require changes in gene expression.
Which of the following statements best describes chemiosmotic coupling?
The sequential linkage of electron transport and proton pumping to drive ATP synthesis.
Diseases that disrupt the function of mitochondria are particularly harmful to muscle and nerve cells for what reason?
These cells need large amounts of ATP to function normally.
Why can small ions and molecules like glucose not easily cross the lipid bilayer?
They are polar and so cannot easily cross the nonpolar bilayer.
How do the high-energy electrons of activated carriers contribute to forming the high-energy phosphate bonds of ATP?
They are used by the electron-transport chain to make a proton gradient.
Why can electron carriers move a proton from one side of a membrane to the other?
They can accept an electron (along with an H+ from water) on one side of the membrane and then release the H+on the other side of the membrane as they pass the electron to the next carrier.
How do specialized brown fat cells take advantage of oxidative phosphorylation to generate heat?
They contain a carrier protein that dissipates the proton gradient across the inner mitochondrial membrane.
Specific amino acids, including Arg 789 in Ras-GAP and amino acids Gln 61 and Thr 35 in Ras, all play an important role in Ras function. Why are these amino acids important?
They help facilitate GTP hydrolysis by Ras.
What do the phosphorylated tyrosines on activated RTKs do?
They serve as binding sites for a variety of intracellular signaling proteins.
IP3 signaling helps regulate sweating, which is important for regulating body temperature. Anhidrosis, the inability to sweat normally, can be caused by genetic and environmental factors. A rare mutation has been identified in a family with several children suffering from anhidrosis. The mutation inactivates the protein that IP3 binds on the ER membrane. Suppose cells were isolated from affected family members and exposed to different treatments. Which of the following treatments would be able to repair the signaling defect in cells isolated from these patients?
addition of high amounts of Ca2+ in the cytosol
Cardiac muscle cells contain a Na+/Ca2+ transporter responsible for maintaining a low cytosolic Ca2+ concentration, which helps regulate cardiac muscle contraction. Ca2+ is transported out of the cell as Na+ is brought into the cell. What type of transporter is this protein?
antiport
When activated by the binding of Ca2+, calmodulin relays the Ca2+ signal onward by doing what action?
binding to Ca2+/calmodulin-dependent protein kinases
What is required for PKC activation?
binding to DAG and continuing presence of Ca2+
Which of the following would increase phosphorylation of CREB by PKA?
blocking binding of the regulatory subunits to the catalytic subunits of PKA
Curare is a chemical purified from the bark of a South American vine, Chondrodendron tomentosum. South American native hunters place the curare on arrow tips. Animals shot with these arrows die from respiratory failure. Derivatives of curare have also been developed for medical use as a muscle relaxant that causes paralysis of muscles during surgery or other procedures. In this case, the muscle cell is the postsynaptic cell. Which of the following potential drug mechanisms would fit with the main outcome of muscle paralysis?
competitive inhibitor of the ligand-gated ion channel on the postsynaptic cell
SARS-COV2 virus has one identified receptor on host cells to date- the ACE2 receptor.
false
Following the binding of an extracellular signal molecule, receptor tyrosine kinases (RTKs) do which of the following?
form dimers in which each polypeptide chain cross-phosphorylates the cytoplasmic tail of its partner.
It is energetically favorable for protons to flow in which direction?
from the intermembrane space to the mitochondrial matrix
In the electron-transport chain, as electrons move along a series of carriers, they release energy that is used to do what?
pump protons across a membrane
The movement of electrons through the electron-transport chain in mitochondria does which of the following?
pumps protons out of the mitochondrial matrix
During an action potential, which of the following actions does not help return the membrane to its resting potential?
the opening of voltage-gated Na+ channels
Alterations in signaling in the pituitary gland can lead to human disease. The GH-releasing hormone (GHRH) stimulates release of growth hormone (GH) from the pituitary gland by binding to GHRH receptors, which are G-protein-coupled receptors. Excessive activity of the GHRH signaling pathway leads to excessive release of growth hormone, which can lead to acromegaly, a form of gigantism. Some patients can reach more than 8 feet tall as they continue to grow even in adulthood.Consider steps that could be taken to reduce GH release. Sort each of the following interventions into the proper category.
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Electron microscopy has been used to identify the structures inside chloroplasts. Determine whether each of the following statements about the structure of chloroplasts is true or false and sort them into the correct box.
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Given the type of transporter as determined in Part 1, choose all of the correct statements below that relate to the function of the Na+/Ca2+ transporter.
-The transporter uses the Na+ electrochemical gradient as an energy source for transporting ions. -Ca2+ is transported against its electrochemical gradient.
Increases GH Release
-Block binding of arrestin to the receptor -Block hydrolysis of GTP
The concentration of free Ca2+ in the cytosol of an unstimulated cell is kept low compared with its concentration in both the extracellular fluid and the endoplasmic reticulum. Which of the following help to maintain this difference?
-Ca2+ pumps in the ER membrane -Ca2+ pumps in the plasma membrane
Which of the following characteristics of K+ channels are important for the selectivity for K+ rather than other ions?
-Carbonyl groups line the wall of the pore. -Four rigid protein loops line the narrowest part of the pore.
Acetylcholine is
-Excitatory in skeletal muscle -Inhibitory in cardiac muscle -Excitatory in salivary glands
Which activated carriers are produced by the citric acid cycle?
-FADH2 -GTP -NADH
Decreases GH Release
-Inhibit interaction of Gα with receptor -Block ligand binding to receptor -Activate phosphorylation of the receptor by GRK kinase
The purpose of the photosynthetic reaction center is to convert captured light energy into chemical energy in the form of transferrable excited electrons. Choose all of the statements that correctly describe the photosynthetic reaction center structure.
-It spans the lipid bilayer of the thylakoid membrane. -It contains four protein subunits. -It contains one peripheral cytochrome subunit.
Which of the following steps are required in the activation of the G-protein signaling pathway?
-Ligand binds to the G-protein-coupled receptor. -Gα exchanges GDP for GTP. -Activated Gα influences target proteins.
Postsynaptic Cell
-Neurotransmitter binding begins a new action potential. -Ligand-gated ion channels open in response to neurotransmitter.
Presynaptic Cell
-Neurotransmitter is released into the synaptic cleft. -Voltage-gated Ca2+ channels open. -Reuptake of the neurotransmitter occurs.
Ras can exist in two different conformations or states, inactive and active. Which of the following correctly describe(s) the stably active state of Ras?
-Switch 1 and switch 2 regions are in an active conformation. - Ras is bound to GTP.
Which of the following characteristics of aquaporins ensure that the channel selectively transports only water molecules and not other solutes?
-The channel has a narrow pore that is only wide enough for a single water molecule to pass through -Two asparagines in the center of the pore prevent protons from passing through the channel.
False Statements
-The chloroplast envelope consists of three concentric membranes. -The space inside the thylakoid membranes is called the stroma.
Protons are pumped across the mitochondrial inner membrane as electrons are transferred through the mitochondrial electron transport chain. Which of the following statements about proton pumping are correct?
-The mitochondria use the proton gradient to synthesize ATP. -The pH inside the mitochondrial matrix is higher than in the intermembrane space. -The NADH dehydrogenase, cytochrome b-c1, and cytochrome oxidase complexes all pump protons across the membrane.
Which of the following events occur in the hypothalamus of a mouse brain expressing channelrhodopsin when the blue light is switched on?
-The neuron membrane is depolarized. -Channelrhodopsin is activated and opened. -Na+ floods into the neuron.
True Statements
-The stroma surrounds the thylakoid membranes. -Grana thylakoids are stacked. -Stroma thylakoids interconnect the grana.
Intracellular Ca2+ levels are important in cardiac muscle. Increasing intracellular Ca2+ levels in heart muscle cells leads to an increase in muscle contraction. Lowering the intracellular Ca2+ levels decreases the strength of cardiac muscle contraction.Congestive heart failure can occur when the heart's pumping of blood is weaker than normal, which leads to fluid collecting around organs, including the heart. One treatment method is to give the patient drugs that increase the strength of the heart muscle contraction. Which of the following might function as an effective treatment of congestive heart failure by increasing the strength of heart muscle contraction?
-a diuretic drug that triggers removal of excess Na+ from the body -a drug that decreases the activity of the Na+/Ca2+ transporter -a drug that inhibits the Na+-K+ pump from establishing a strong Na+ gradient
Which of these processes require a membrane?
-generation of ATP by photosynthesis in plants -generation of ATP by oxidative phosphorylation -generation of energy by mitochondria -generation of ATP by photosynthesis in bacteria
Which of the following alterations to the signaling pathway would lead to increased transcription by the CREB protein?
-inhibition of cAMP breakdown -inhibition of GTP hydrolysis
ATP synthase is a large molecular machine that converts the energy in an electrochemical gradient into the bond energy stored in ATP. Which of the following events are required for the synthesis of ATP?
-rotation of the rotor in the membrane -movement of protons down their gradient through ATP synthase -conformational changes of the F1 ATPase
Which of the following are activated by many receptor tyrosine kinases (RTKs)?
-the MAP-kinase signaling module -phospholipase C -phosphoinositide 3-kinase -the monomeric GTP-binding protein Ras
Approximately how many molecules of ATP can be produced in mitochondria from the complete oxidation of a single glucose molecule?
30
The drug 2,4-dinitrophenol (DNP) makes the mitochondrial inner membrane permeable to H+. The resulting disruption of the proton gradient inhibits the mitochondrial production of ATP. What additional effect would DNP have on the transport of ATP out of the mitochondrial matrix?
ATP export will decrease because its carrier exploits the difference in voltage across the inner membrane.
What happens when ATP synthase operates "in reverse" and pumps H+ across a membrane against its electrochemical proton gradient?
ATP is hydrolyzed to form ADP and Pi.
Suppose the shaft of ATP synthase that is attached to the rotor were truncated (shortened) such that it no longer extended into the F1ATPase head. What would be the consequence of this mutation?
ATP would not be produced because the conformation of the F1 ATPase head would not be changed.
Why would a cell express the aquaporin protein if water can cross the membrane in the absence of aquaporin?
Aquaporin facilitates the faster movement of water molecules across the membrane.
Ions in solution are found in a hydration shell of water. This shell must be removed for an ion to pass through the channel. How does the K+ channel accomplish removal of the water from the shell around the ion?
Carbonyl groups lining the wall of the pore can interact with the unsolvated K+ ion, balancing the energy needed to remove the hydration shell.
Which statement regarding the ratio of ATP and ADP concentrations in the cell cytosol is accurate?
Cells keep the concentration of ATP in the cytosol about 10 times higher than that of ADP.
The electrochemical driving force on a given hanged solute particle
Combines the free energies available from the solutes concentration gradient and the cells membrane potential.
Which statement about cell signaling is correct?
Each receptor is generally activated by only one type of signal molecule.
Which is true about electrons as they move through the electron-transport chain?
Electrons start out at very high energy and lose energy at each transfer step along the electron-transport chain.
Why does optogenetics hold the potential to help scientists better understand neurobiology?
Optogenetics can be used to analyze neural circuits and complex behavior.
The glucose-Na+ symport transports glucose into the epithelial cells lining the gut. How would import of glucose into the cells be affected by addition of a leaky Na+ channel to their plasma membrane?
Glucose transport would slow because the Na+ gradient is dissipated by the Na+ channel.
Investigators introduce two proteins into the membrane of artificial lipid vesicles: (1) an ATP synthase isolated from the mitochondria of cow heart muscle, and (2) a light-activated proton pump purified from the prokaryote Halobacterium halobium. The proteins are oriented as shown in the diagram. When ADP and Pi are added to the external medium and the vesicle is exposed to light, would this system produce ATP?
No, because ATP synthase is not oriented correctly.
Investigators introduce two proteins into the membrane of artificial lipid vesicles: (1) an ATP synthase isolated from the mitochondria of cow heart muscle, and (2) a light-sensitive proton pump purified from the prokaryote Halobacterium halobium. The proteins are oriented as shown in the diagram. To this preparation, the investigators add a drug called 2,4-dinitrophenol (DNP), which makes the vesicle membrane permeable to H+. When ADP and Pi are added to the medium outside the vesicle, and the DNP-treated vesicles are exposed to light, will ATP be produced?
No, because the DNP will collapse the H+ gradient that ATP synthase uses to generate ATP.
Which of the following statements is not true regarding active transport by transmembrane pumps?
Some solutes are transported across the membrane in tandem with other molecules, both moving from lower concentration to higher concentration.
Which of the following drives the production of ATP from ADP and Pi by ATP synthase?
a proton (H+) gradient
In photosynthesis, what drives the generation of ATP by ATP synthase?
a proton gradient across the thylakoid membrane
The movement of an ion against its concentration gradient is called what?
active transport
Individuals with inherited diseases causing mitochondrial dysfunction typically experience which of the following symptoms?
heart problems
What condition must exist for glucose to be transported into a cell using the glucose-Na+ symport?
high Na+ concentration outside the cell
Which part of the mitochondrion contains the proteins that carry out oxidative phosphorylation?
inner membrane
Which metal ion is found in all three respiratory enzyme complexes?
iron
Which part of the mitochondrion contains porins?
outer membrane
Stage 1 of photosynthesis is, in large part, equivalent to what process?
oxidative phosphorylation
