Exam 4
When cells respond to an extracellular signal, they most often convert the information carried by this molecule from one form to another. What is this process called?
signal transduction
Why does nitric oxide (NO) act as a paracrine signal that affects only neighboring cells?
t is rapidly converted to nitrates and nitrites in the extracellular fluid.
What makes it possible for a combination of signal molecules to evoke a response that differs from the sum of the effects that each signal could trigger on its own?
the ability of different intracellular relay systems to interact
The NADH generated during glycolysis and the citric acid cycle feeds its high-energy electrons to which of the following?Choose one:ADPH2Othe electron transport chainFADthe citric acid cycle
the electron transport chain
Which does not contain both actin and myosin?
the lamellipodium at the leading edge of a crawling cell
Which membrane-enclosed organelles most likely evolved in a similar manner?
the nucleus and the ER
Which molecules are required for the citric acid cycle to fully oxidize the carbons donated by acetyl CoA?Choose one or more:oxaloacetateGDPGTPATPNAD+O2
oxaloacetate GDP NAD+ O2
Which of the following cytoskeletal structures are the most common for providing tracks for guiding intracellular transport?
. microtubules
Assume five molecules of FADH2 are made in the citric acid cycle in a given amount of time. How many NADH are made during the same time interval?
15
How many kinetochores are present in a human cell during mitosis?
92
The goal of gene-therapy techniques is to provide cells with functional copies of mutated genes. One technique involves introducing functional genes on an "artificial chromosome." Somatic cells in which the artificial chromosome has been inserted have 47 chromosomes instead of the normal 46 (i.e., for human cells). To be effective, the artificial chromosome must be passed to daughter cells during mitosis, which requires that the artificial chromosome contain sequences on which kinetochores can assemble. With this in mind, what should designers of artificial chromosomes include to ensure proper kinetochore assembly on the artificial chromosome?
A. centromere
Most of the energy released by oxidizing glucose is saved in the high-energy bonds of what molecules?Choose one:ADP and other activated carriers H2O and CO2 GDP and other activated carriers O2 ATP and other activated carriers
ATP and other activated carriers
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.
Which of the following signaling pathways would be likely to trigger the most rapid cell response?
Acetylcholine binds to anion-channel-coupled receptor that allows Na+ to flow down its electrochemical gradient, triggering contraction of a skeletal muscle cell.
Weight loss can occur when glucose is oxidized to CO2 rather than being stored as glycogen. The first step in glucose oxidation is glycolysis. A 1930s diet drug, DNP, made the inner mitochondrial membrane permeable to protons, increasing the rate of glycolysis. What is the explanation for the DNP-induced increase in glycolysis? A. High AMP inhibits phosphofructokinase.B. High ADP activates phosphofructokinase.C. DNP also makes the inner mitochondrial membrane leaky to glucose, increasing the ability of the mitochondria to perform glycolysis.D. High ATP activates phosphofructokinase.
B. High ADP activates phosphofructokinase.
Which statements below accurately describe an aspect of the citric acid cycle?Choose one or more:A. The citric acid cycle produces two kinds of high-energy molecules, GTP and NADH.B. NADH is generated in steps 3, 4, and 8.C. Oxaloacetate is regenerated by the end of the citric acid cycle.D. The two carbons that enter as acetyl CoA are released in the same cycle as CO2.
B. NADH is generated in steps 3, 4, and 8. C. Oxaloacetate is regenerated by the end of the citric acid cycle.
One approach to killing cancer cells is to induce apoptosis. Which of the following are reasonable approaches that researchers can take to induce apoptosis in cancer cells?
B. activating the Bax protein D. inhibiting the Bcl2 protein
Which of the following statements correctly describe an aspect of converting light to chemical energy in chloroplasts? choose one or more
C. Excited electrons are passed through an electron transport chain.D. The energy in excited electrons is used to pump protons across the thylakoid membrane from the stroma to the thylakoid space.
Which of the following describes the structure of an actin filament?
C. It is a twisted chain of actin molecules.
An actin-binding protein called cofilin binds preferentially to ADP-containing actin filaments rather than ATP-containing actin filaments. Based on this preference, which is true?
Cofilin binds to older actin filaments.
Which of the following structural changes is not typically seen in a cell that is undergoing apoptosis?
D. The cell swells.
Your friends are on a low-fat, high-carbohydrate diet, which they claim will prevent fat accumulation within their bodies. They eat tons of pasta and bread without worrying about calorie count. What can you correctly say to your friends about their potential to accumulate lipids on their low-fat diet?Choose one:A. They will accumulate fats because cells have no way of storing carbohydrates.B. They will not accumulate fats because carbohydrates have less energy per gram than fats.C. They will not accumulate fats because cells have no way of storing fats.D. They will accumulate fats because cells can convert glycolytic metabolites into lipids.
D. They will accumulate fats because cells can convert glycolytic metabolites into lipids.
Inside a muscle fiber, what triggers sarcomeres to contract?
D. a sudden rise in cytosolic Ca2+
How do the interiors of the ER, Golgi apparatus, endosomes, and lysosomes communicate with each other?
D. by small vesicles that bud off of one organelle and fuse with another
Which is the toughest and most durable of the different types of cytoskeletal filaments?
D. intermediate filaments
Heart conditions known as cardiomyopathies include two main subtypes. In hypertrophic cardiomyopathies, the heart muscle becomes stiff. Such disorders can be treated by drugs like verapamil, which block calcium channels. In a second class of cardiomyopathies, the heart muscle becomes dilated. These disorders are sometimes treated with the drug digoxin, which blocks Na+ pumps and elevates intracellular Ca2+ in cardiac muscle cells. Both types of disorder can be caused by mutations in the genes encoding troponin. Some of these mutations increase troponin's sensitivity to Ca2+; other mutations reduce it. Based on the treatment protocols outlined, what type of mutation is responsible for hypertrophic cardiomyopathy?
E. mutations that increase troponin's sensitivity to Ca2+
Proteins destined for the Golgi apparatus, endosomes, lysosomes, and even the cell surface must pass through which organelle?
ER
Which statement about cell signaling is correct?
Each receptor is generally activated by only one type of signal molecule.
Which of the following observations, made in malonate-treated muscle, led Krebs to believe that this set of reactions is cyclical?Choose one:If citrate were added, succinate would accumulate.If succinate were added, fumarate would accumulate.Regardless of what he added, oxaloacetate would accumulate.If fumarate were added, succinate would accumulate.Regardless of what he added, large amounts of oxygen would be produced.
If fumarate were added, succinate would accumulate.
When ATP and food molecules such as fatty acids are abundant, which will occur?Choose one: Enzymes involved in glycolysis will break down glucose to generate pyruvate. When food molecules are plentiful, neither glycolysis nor gluconeogenesis will occur. Enzymes involved in glycolysis will operate in the reverse direction, using pyruvate to produce glucose. When food and ATP are plentiful, both glycolysis and gluconeogenesis will occur. Enzymes involved in gluconeogenesis will use energy to produce glucose.
Enzymes involved in gluconeogenesis will use energy to produce glucose.
Most of the diversity in the rates of cell division in the adult body lies in variations in the time that each cell spends in which phase(s)?
G1 phase and G0 phase
Dynamic instability in microtubules stems from the intrinsic capacity of tubulin molecules to hydrolyze what?
GTP
Which organelle receives proteins and lipids from the endoplasmic reticulum, modifies them, and then dispatches them to other destinations in the cell?
Golgi apparatus
In a culture of green alga that is carrying out photosynthesis in the presence of CO2 in the laboratory, what would happen to the levels of ribulose 1,5-bisphosphate and 3-phosphoglycerate in the minutes after the lights were turned off and the cultures were plunged into darkness?
In a culture of green alga that is carrying out photosynthesis in the presence of CO2 in the laboratory, what would happen to the levels of ribulose 1,5-bisphosphate and 3-phosphoglycerate in the minutes after the lights were turned off and the cultures were plunged into darkness?
n a motility assay, investigators attach myosin motor proteins to a glass slide and then add actin filaments. Once the filaments have bound to myosin, what can be expected to occur?
In the presence of ATP, the filaments will glide toward their minus ends.
When activated phospholipase C cleaves an inositol phospholipid, what happens to the small signaling molecules the enzyme produces?
Inositol 1,4,5-trisphosphate (IP3) is released into the cytosol, while diacylglycerol is retained in the membrane.
Which statements are true of receptor-mediated endocytosis?
It allows the internalization of extracellular substances in clathrin-coated vesicles. It allows cholesterol-carrying low-density lipoproteins (LDLs) to be taken up by cells. The process can be hijacked by viruses to gain entry into cells.
The drug Viagra promotes blood vessel dilation by prolonging signaling through nitric oxide (NO). How does Viagra boost NO?
It blocks the enzyme that degrades cyclic GMP.
What happens to the ATP produced during stage 1 of photosynthesis?
It is consumed within the chloroplast to produce glyceraldehyde 3-phosphate.
Although the citric acid cycle itself does not use O2, it requires a functioning electron transport chain (which uses O2) in order to regenerate which molecule for further use in the citric acid cycle?Choose one:ATPNAD+ADPFADH2NADH
NAD+
Which statement is true of glycogen phosphorylase?Choose one: It is activated by glucose 6-phosphate, but inhibited by ATP.It stimulates gluconeogenesis. It is inhibited by glucose 6-phosphate, but activated by ATP .It is activated by glucose 6-phosphate and by ATP. It is inhibited by glucose 6-phosphate and by ATP.
It is inhibited by glucose 6-phosphate and by ATP.
What must happen for a Cdk to be active?
It must bind to its cyclin partner.
What is true about the phosphorylation of condensins by M-Cdk?
It triggers their assembly onto DNA, compressing chromosomes into a more compact form.
t is often useful for scientists to study a population of cells that are all at the same stage of the cell cycle. For example, the discovery of cyclins and Cdks was enabled by studying frog eggs that divided synchronously after fertilization; extracts from the embryos were thus representative of the cell-cycle stage at which the extract was made. Researchers have devised means to synchronize asynchronous populations of cultured cells. For example, serum starvation deprives cells of mitogens and blocks cells in the G0/G1 phase of the cell cycle. Another method involves gently shaking culture flasks and harvesting the cells that release from the substratum. In what stage of the cell cycle are these cells most likely to be?
M phase
When a muscle is stimulated to contract, myosin heads walk along actin filaments in repeated cycles of attachment and detachment. Which of the following represents a correct description of the events in this cycle?
Myosin attaches to actin; ATP binding reduces the affinity of myosin for actin; myosin is "cocked" as its head is displaced along the actin filament; the power stroke puts myosin in a "rigor" configuration.
n eukaryotic cells, what is the final electron acceptor in the electron transport chain?Choose one:ATPO2FADH2CO2NAD+
O2
A subset of breast cancers overexpress the receptor tyrosine kinase (RTK), known as human epidermal growth factor receptor 2 (HER2). Patients with HER2-positive breast cancers often benefit from treatment with a HER2-binding antibody known as Pertuzumab. Given that antibodies are large proteins that cannot cross the cell membrane, what might be directly impacted by Pertuzumab to limit cell proliferation?
Pertuzumab prevents receptor dimerization.
Which proteins play a central role in the fusion of a vesicle with a target membrane?
SNAREs
Which statement about signaling through GPCRs is correct?
Some G proteins inhibit the production of cyclic AMP.
Which of these represents a mechanism used to terminate a signal transmitted by activated RTKs?
The RTKs are internalized and digested in lysosomes.
Ethylene is a hormone that promotes the ripening of fruit. What happens in the absence of ethylene?
The activated ethylene receptor promotes the degradation of a transcription regulator and the ethylene-responsive genes remain turned off.
Antibiotics should inhibit bacterial cell growth without generating side effects in the human patient, but that is not always the case. Some antibiotics that inhibit bacterial protein synthesis by binding to bacterial ribosomes induce negative side effects in patients. What is the most likely cause of these side effects?
The antibiotics interfere with mitochondrial ribosomes.
The buildup of lactic and formic acids generated by anaerobic fermentation likely favored the evolution of which of the following?
The buildup of lactic and formic acids generated by anaerobic fermentation likely favored the evolution of which of the following?
The activity of a kinase called Src is regulated by phosphorylation. The kinase is inactivated by phosphorylation at a C-terminal tyrosine residue (Tyr527) and is activated by interaction with an activated RTK, which stimulates Src to autophosphorylate a different tyrosine residue (Tyr416). Full activation of Src requires removal of the inhibitory phosphate group and binding to an activated RTK.Based on this information, which statement about the activity of Src kinase is correct?
The kinase is active only when Tyr527 is dephosphorylated and Tyr416 is phosphorylated.
If GTP hydrolysis occurs on a tubulin molecule at the plus end of a microtubule protofilament before another tubulin molecule is added, what typically happens?
The microtubule depolymerizes.
Investigators incubate myosin with an ATP analog that can bind to myosin but cannot be hydrolyzed. What effect will this treatment have on the activity of myosin?
The myosin will be unable to bind to an actin filament.
Which of the following statements is false?
The pairing of homologous chromosomes during prometaphase is called bi-orientation.
To determine whether a signal sequence directs proteins to a particular organelle, researchers prepare two versions of the same protein: one version contains the signal sequence, while the other lacks it. They label the protein that contains the signal sequence with a radioactive marker, and then incubate both of the proteins with the organelle of interest.After allowing enough time for any of the proteins to be transported into the organelle, a protease is added to the mixture.If the signal sequence is the correct one for the selected organelle, what would the researchers likely see?
The radioactive label would be associated with an intact protein.
How do enzymes maximize the energy harvested from the oxidation of food molecules?Choose one:They allow a larger amount of energy to be released from food molecules such as glucose.They allow what would otherwise be an energetically unfavorable oxidation reaction to occur.They guarantee that each reaction involved in the oxidation of food molecules proceeds in just one direction.They allow the stepwise oxidation of food molecules, which releases energy in small amounts.They allow oxidation reactions to take place without an input of activation energy.
They allow the stepwise oxidation of food molecules, which releases energy in small amounts.
What is true of the GTP-binding proteins that act as molecular switches inside cells?Choose one:
They are active when GTP is bound.
Which statement about intermediate filaments is not true?
They rupture under stress.
What do the phosphorylated tyrosines on activated RTKs do?
They serve as binding sites for a variety of intracellular signaling proteins.
They are active when GTP is bound.
They transduce signals in a simple and direct manner.
Because cyclic AMP diffuses quickly through the cytosol and a cyclic AMP phosphodiesterase rapidly converts cyclic AMP to AMP, what is the consequence?
he cytosolic concentration of cyclic AMP can change rapidly.
Which two-carbon molecule enters the citric acid cycle?Choose one:carbon dioxidepyruvateacetyl CoAcitrateoxaloacetate
acetyl CoA
What is the contractile ring made of?
actin and myosin
Which response to GPCR stimulation would be most rapid?
activation of a G protein that regulates the opening of an ion channel
n cells, pyruvate can be converted to which of the following?Choose one or more:alanine oxaloacetate glucose acetyl CoA lactate
alanine oxaloacetate glucose acetyl CoA lactate
The proton gradient that drives ATP synthesis during photosynthesis is generated by which of the following?
an electron carrier that pumps protons out of the stroma into the thylakoid space
Which of the following occurs during metaphase?
chromosomes being aligned under tension
Phagocytosis is a process by which cells do which of the following?
consume large particles, such as microbes and cell debris
Most mitochondrial and chloroplast proteins are made within which part of the cell?
cytosol
The entire period between one M phase and the subsequent M phase is called what?
interphase
As a cell grows, which microtubule-associated protein pulls the ER membrane outward, stretching it like a net?
kinesin
Microtubules capture chromosomes by binding specifically to which of the following?
kinetochores on the sister chromatids
What do cells do during G1 phase?
destroy cyclins repair DNA damage
What is the name of the thin, sheetlike structures that a fibroblast regularly extends during cell crawling?
lamellipodia
What is the mitotic spindle made of?
microtubules
The outer membrane of the nucleus is continuous with the membrane of which other organelle?
endoplasmic reticulum
You are packing for a hiking trip during which you'll be burning a lot of calories with physical activity. You want to pack as efficiently as possible since you need to carry a tent and all your food. You can get the most calories out of 5kg of food if it is in the form of
fat
After an overnight fast, most of the acetyl CoA entering the citric acid cycle is derived from what type of molecule?Choose one:glycogen glucose amino acids fatty acids pyruvate
fatty acids
Where does the oxidative (oxygen-dependent) stage of the breakdown of food molecules occur in a eukaryotic cell?Choose one:endoplasmic reticulumcytosolGolgi apparatusmitochondrion
mitochondrion
When a cell is acutely injured, it usually dies by which process?
necrosis
Intermediate filaments are found in what structure?
nuclear lamina
Under anaerobic conditions, which metabolic pathway regenerates the supply of NAD+ needed for glycolysis?Choose one:formation of acetyl CoAfermentationcitric acid cyclebreakdown of fatsbreakdown of amino acids
fermentation
Botulism is a potentially fatal foodborne disease caused by the bacterium Clostridium botulinum. C. botulinum produces different toxins, several of which are proteases that cleave neuronal SNARE proteins. What normal process is blocked by cleavage and inhibition of SNARE proteins?
fusion of vesicles with target membranes
When food is plentiful, animals can store glucose as what?
glycogen
Many of the extracellular signal molecules that regulate inflammation are released locally at the site of infection. What form of cell-cell signaling is being used?
paracrine
Mutations that prevent Bcl2 family proteins Bax and Bak from interacting with the outer mitochondrial membrane would have which effect?
preventing the release of cytochrome c and inhibiting apoptosis
The mitotic spindle begins to assemble in which phase of the cell cycle?
prophase
In a typical human secretory cell, which of the following membranes has the largest surface area?
rough ER
What are small intracellular signaling molecules often called?
second messengers
In the absence of oxygen, in cells that cannot carry out fermentation, glycolysis would halt at which step?Choose one:the oxidation of glyceraldehyde 3-phosphate to 1,3-bisphosphoglyceratethe phosphorylation of fructose 6-phosphate to fructose 1,6-bisphosphatethe reversible rearrangement of glucose 6-phosphate to fructose 6-phosphatethe transfer of a phosphate group from 1,3-bisphosphoglycerate to ADP to form ATP
the oxidation of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate
What does the term "gluconeogenesis" refer to?Choose one:the release of glucose from molecules such as glycogenthe breakdown of glucose during glycolysisthe transport of glucose across a cell membranethe synthesis of glucose from small organic molecules such as pyruvatethe breakdown of glucose during fermentation
the synthesis of glucose from small organic molecules such as pyruvate
Through which of the following do proteins travel from one cisterna to the next in the Golgi apparatus?
transport vesicles that bud from one cisterna and fuse with the next
In what form do plant and animal cells store fat?
triacylglycerol
The anaphase-promoting complex (APC) triggers the onset of anaphase by doing which of the following?
triggering the destruction of the cohesins that hold the sister chromatids together
How are newly made lipids supplied to the plasma membrane?
via the constitutive pathway of exocytosis
Researchers studying yeast discovered that, for some mutants, when the temperature at which the cells are grown is elevated from 25ºC to 37ºC, their secretory pathway no longer functions and the cells grow dense with unsecreted protein.When these cells are examined microscopically, they can be divided into groups that vary in terms of where the unsecreted proteins accumulate. In some of the mutants, proteins accumulate in the ER; in others, the Golgi; in others, they accumulate in vesicles near the plasma membrane.What is the likely explanation for this difference in appearance?
Different temperature-sensitive mutations affect different stages of the transport process.
Kinesin-5 is a motor protein that binds to overlapping interpolar microtubules near the midzone of the mitotic spindle. Each of these kinesin proteins has two motor domains that walk toward the plus ends of the microtubules to which the kinesin is bound. When is this kinesin active and how does it affect the spindle?
During anaphase B, kinesin-5 slides the microtubules past one another toward the spindle poles, pushing the poles apart and lengthening the spindle.
