Bio exam 3 smart works
Porin proteins—which form large, water-filled pores in mitochondrial and bacterial outer membranes—fold into β-barrel structures. The amino acids that face the outside of the barrel have what kind of side chains?
hydrophobic
Insulin is synthesized in the form of a precursor protein that requires cleavage of two different peptide segments before the mature protein is secreted from β cells in the pancreas. The first peptide is removed when the protein enters the lumen of the ER. To find out when the second cleavage event takes place, investigators prepare a pair of antibodies: one recognizes the pro-insulin precursor, the other the mature insulin protein. They tag the antibody that binds to the precursor protein with a red fluorescent marker; the antibody that binds to mature insulin is tagged with a green fluorescent marker. When both markers are present, the sample fluoresces yellow. The investigators then incubate an isolated β cell with both antibodies at the same time and monitor the fluorescence in its various membrane-bound compartments. The data are shown in the table below. Based on these observations, where is the second peptide removed from the pro-insulin precursor protein?
immature secretory vesicles
How does the inclusion of cholesterol affect animal cell membranes?
It tends to make the lipid bilayer less fluid.
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.
Which molecules are required for the citric acid cycle to fully oxidize the carbons donated by acetyl CoA?
-O2 -GDP -NAD+ -oxaloacetate
Many viruses enter cells through receptor-mediated endocytosis. Which of the following strategies could be affective in blocking entry of this class of viruses into cells and could be used to treat viral infections?
- Block the function of adaptin. - Block the receptor with an antibody.
Which of the following statements are true of electron transfer in the electron-transport chain?
- Electrons move toward molecules with a high redox potential. -NADH is a strong electron donor. -Each electron transfer is an oxidation-reduction reaction.
Which statements are true of receptor-mediated endocytosis?
- It allows cholesterol-carrying low-density lipoproteins (LDLs) to be taken up by cells. - It allows the internalization of extracellular substances in clathrin-coated vesicles. - The process can be hijacked by viruses to gain entry into cells.
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 NADH dehydrogenase, cytochrome b-c1, and cytochrome oxidase complexes all pump protons across the membrane. - The pH inside the mitochondrial matrix is higher than in the intermembrane space.
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.
The FRAP technique occurs in a series of steps. Select every statement that correctly describes a step in the FRAP procedure.
-The relative mobility of the fluorescently labeled molecule is measured. - The molecule of interest is fluorescently labeled.
In this illustration of the structure of ATP synthase, which of the components rotate?
1 & 5
there are two properties of phospholipids that affect how tightly they pack together: the length of the hydrocarbon chain and the number of double bonds. the degree of packing in turn, influences the relative mobility of these molecules in the membrane. which of the following would yield the most highly mobile phospholipid ?
15 carbons with 2 double bonds
the Na+/K+ ATPase pump actively moves
3 Na+ out and 2 K+ in
If an ER signal sequence were added to its N-terminus, which structure would the engineered protein adopt?
A.
Which activated carrier contains a high-energy bond whose hydrolysis releases a large amount of free energy?
ATP
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 is true of lysosomes?
An ATP-driven H+ pump in the lysosomal membrane maintains the organelle's pH.
How do transporters and channels select which solutes they help move across the membrane?
Channels discriminate between solutes mainly on the basis of size and electric charge; transporters bind their solutes with great specificity in the same way an enzyme binds its substrate.
The following graphs show the number of adherent leukocytes found on the blood vessel wall in control conditions and after adding a selectin inhibitor, which blocks the function of selectin. Which of the following graphs correctly shows the effect of a selectin inhibitor on adherence of leukocytes to the vessel wall?
Blocking selectins would block the ability of selectin to bind leukocytes, so leukocytes would be less likely to move slowly along the vessel wall and cause a blockage of red blood cells.
Not all fat cells are equivalent. Humans and other animals contain both white fat cells and brown fat cells, named after their color. Because increases in brown fat cells may aid weight loss, researchers are interested in factors that control the ratio of white fat cells and brown fat cells, as detailed in a 2017 article in Obesity Reviews. What is the mechanism for how brown fat cells aid weight loss?
Brown fat cell mitochondria contain an uncoupling protein.
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.
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.
Proteins destined for the Golgi apparatus, endosomes, lysosomes, and even the cell surface must pass through which organelle?
ER
The following graphs show the number of adherent leukocytes found on the blood vessel wall in control conditions and after adding a selectin inhibitor, which blocks the function of selectin. Which of the following graphs correctly shows the effect of a selectin inhibitor on adherence of leukocytes to the vessel wall?
GRAPH B
During electron transport, which serves as a ready source for protons that can be pumped across the membrane?
H2O
In one experiment, investigators create a liposome—a vesicle made of phospholipids—that contains a solution of 1 mM glucose and 1 mM sodium chloride. If this vesicle were placed in a beaker of distilled water, what would happen the fastest?
H2O would diffuse in.
As a polypeptide is being translocated across the membrane of the endoplasmic reticulum, a stop-transfer sequence can halt the process. What eventually becomes of this stop-transfer sequence?
It forms an α-helical membrane-spanning segment of the protein.
The drug scopolamine is used to treat dizziness, motion sickness, and smooth muscle spasms. When isolated muscle cells are incubated with scopolamine, addition of acetylcholine no longer depolarizes the muscle cell membrane or stimulates muscle cell contraction. Which would best explain how scopolamine exerts its muscle-relaxing effects?
It inhibits the opening of acetylcholine-gated Na+ channels in the muscle cell membrane.
When a neuron is activated by a stimulus, its plasma membrane will change until it reaches a membrane potential of about +40 mV. What is special about this value?
It is approximately the membrane potential at which the electrochemical gradient for Na+ is zero.
Lipid bilayers are highly IMPERMEABLE to which molecule(s)?
Na+ and Cl-
which of the following is an example of indirect active transport?
Na+/amino acid symport
Most sports drinks contain both carbohydrates and salts. The carbohydrates replace glucose burned during exercise and the salts replace salts lost in sweat. The salt also helps the small intestine absorb glucose. Pick the answer that accurately describes which salt is most beneficial for glucose absorption.
NaCl, because Na+ is needed for glucose entry.
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 Piare 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.
How does the nuclear pore restrict the passage of large molecules that do not bear the correct nuclear localization signal?
Nuclear pore proteins contain disordered segments that form a gel-like meshwork inside the pore.
What is true of protein glycosylation in the ER?
Oligosaccharides are added by an enzyme that has its active site on the lumenal side of the ER membrane.
Below is a table listing the reactions that constitute the 10 steps of glycolysis, along with the change in free energy (ΔG°) for each step. Based on the data, which steps in glycolysis are effectively irreversible?
Steps 1, 3, and 10
Fluorescence recovery after photobleaching (FRAP) is used to monitor the movement of fluorescently labeled molecules within the plane of a cell membrane. The molecules labeled are often proteins, but lipids can be labeled too. How would the curve that represents FRAP for labeled proteins compare to the curve representing labeled lipids?
The FRAP curve for lipids would show a much more rapid recovery to initial levels of fluorescence.
When the net charge on either side of the plasma membrane is zero, what else is true? (a) There is an equal number of K+ ions on each side of the plasma membrane. (b) The K+ leak channels are open. (c) The electrochemical potential across the membrane is zero. (d) The resting membrane potential is between -20 mV and -200 mV.
The electrochemical potential across the membrane is zero.
Your friend now has the pumps successfully pumping ions. She added an equal concentration of both ions to the correct sides of the liposomes along with an excess of the energy source. She is surprised when the pumps stop working after a short time. Which of the following could explain why the transporter stopped pumping ions?
The pump ran out of Na+ to pump because it pumps 3 Na+ out for every 2 K+pumped in.
Which of the following would be most likely to disrupt lipid bilayer formation?
addition of a phosphate to the end of the lipid tail
When the transport vesicle shown below fuses with the plasma membrane, which monolayer will face the cell cytosol?
The orange monolayer will face the cytosol.
ATP is important for chaperone protein function. Why would protein import into mitochondria be disrupted if ATP were depleted from inside mitochondria?
The protein could slip back out of the mitochondria during transport.
The drug vinblastine disrupts microtubule polymerization. How would adding vinblastine to a cell affect the constitutive secretory pathway?
Transport vesicles will not be brought to either the Golgi apparatus or the plasma membrane.
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.
In bacteria, the transport of many nutrients, including sugars and amino acids, is driven by the electrochemical H+ gradient across the plasma membrane. In E. coli, for example, an H+-lactose symporter mediates the active transport of the sugar lactose into the cell. Given what you know about coupled transport, which is likely true of the H+-lactose symporter?
The transporter oscillates randomly between states in which it is open to either the extracellular space or the cytosol.
What happens to proteins with no signal sequence that are made in the cytosol?
They remain in the cytosol.
Formation of a lipid bilayer is energetically favorable. How does this arrangement result in higher entropy for the system, and thus make bilayer formation energetically favorable? (a) Polar head groups form a hydrogen-bonding network at the interface with water. (b) Water molecules form cagelike structures around hydrophobic molecules. (c) Hydrogen bonds form between neighboring polar head groups in the bilayer. (d) Fatty acid tails are highly saturated and flexible.
Water molecules form cagelike structures around hydrophobic molecules.
To explore how yeast cells metabolize glucose, investigators use a DNA microarray to examine the effect the sugar has on the expression of a variety of genes. Cultured yeast cells are supplemented with high concentrations of glucose. mRNAs are extracted from the cells, converted into cDNAs, and labeled with a fluorescent marker. The samples are then hybridized to a DNA microarray that includes probes representing yeast genes. Shown here is a data set representing genes involved in ribosome biogenesis and electron transport. Red indicates that supplementing the growth medium with glucose has increased the expression of the genes, whereas green indicates that the added glucose has decreased gene expression. Based on this data, what can be concluded about how yeast cells behave when grown in the presence of high concentrations of glucose?
Yeast cells exposed to high concentrations of glucose grow by fermentation.
Which of the following describes the resting membrane potential of a neuron?
a state in which the flow of positive and negative ions across the plasma membrane is precisely balanced
most cells have a negative plasma membrane potential (Vm) because they have
an excess of negatively charged solute molecules inside the cell
Animals exploit the phospholipid asymmetry of their plasma membrane to distinguish between live cells and dead ones. When animal cells undergo a form of programmed cell death called apoptosis, phosphatidylserine—a phospholipid that is normally confined to the cytosolic monolayer of the plasma membrane—rapidly translocates to the extracellular, outer monolayer. The presence of phosphatidylserine on the cell surface serves as a signal that helps direct the rapid removal of the dead cell. How might a cell actively engineer this phospholipid redistribution?
by activating a scramblase and inactivating a flippase in the plasma membrane
The shape of a cell and the mechanical properties of its plasma membrane are determined by a meshwork of fibrous proteins called what?
cell cortex (This meshwork of protein filaments is attached to the underside of the plasma membrane.)
The buildup of lactic and formic acids generated by anaerobic fermentation likely favored the evolution of which of the following?
cells that could pump protons
Phagocytosis is a process by which cells do which of the following?
consume large particles, such as microbes and cell debris
which of the following components of the electron-transport chain does not act as a proton pump?
cytochrome c
Most mitochondrial and chloroplast proteins are made within which part of the cell?
cytosol
consider an erythrocyte with an internal glucose concentration of 0.1 mM and an external glucose concentration of 5nM. Each of the following is true about GLUT1 transport of glucose across the plasma membrane into the cell except
delta G is independent on the concentration gradient
which of the following is a characteristic of facilitated diffusion (passive transport) of a molecule across a membrane? a. its rate is higher than that of simple diffusion of the molecule b. it is highly specific for the molecule being transported c. the direction of transport is determined by concentration and/or electrochemical gradients d. the rate of transport is saturable
e. all of the above are true
The movement of materials from the plasma membrane, through endosomes, and then to lysosomes describes which type of pathway?
endocytic pathway
The outer membrane of the nucleus is continuous with the membrane of which other organelle?
endoplasmic reticulum
During a pulse-chase experiment with secreted proteins, the proteins are synthesized for a short "pulse" time with radioactive or fluorescent amino acids to label the proteins. During the "chase" period, unlabeled amino acids are added, so any additional proteins synthesized are not labeled. The labeled proteins can then be monitored over time. You complete a pulse-chase experiment to monitor the secretion of a protein from the cell. Which of the following correctly lists the order of locations of the protein during the chase period?
endoplasmic reticulum → transport vesicle → Golgi → transport vesicle → secreted
Which cellular compartment acts as the main sorting station for extracellular cargo molecules taken up by endocytosis?
endosomes
the advantage to the cell of the gradual oxidation of glucose during cellular respiration compared with its combustion to CO2 and H2O in a single step is that
energy can be extracted in usable amounts
Glucose enters the cell by which process?
facilitated diffusion
The first living cells on Earth—whether prokaryotes or primitive eukaryotes—most likely generated ATP by what process?
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
Shown here is a gel in which mRNAs purified from the two different trypanosomes have been separated by size and exposed to probes that recognize the three different forms of the PGK gene (genes 1, 2, and 3). Based on these results, which gene most likely encodes the peroxisomal form of PGK?
gene 3
Which organelle receives proteins and lipids from the endoplasmic reticulum, modifies them, and then dispatches them to other destinations in the cell?
golgi apparatus
which of the following types of ion movement might be expected to require co-transport of protons from the mitochondrial inter membrane space to the matrix, in as much as it could not be driven by the membrane potential across the inner membrane? (against its concentration gradient)
import of acetate ions into the matrix from the inter membrane space
The chemistry of many metabolic reactions was deciphered using molecules labeled with radioactive isotopes. If acetyl CoA labeled with radioactive 14C in both carbon positions were fed into the citric acid cycle, where would the radioactivity be after one turn of the cycle?
in oxaloacetate
phosphorylation of glucose following its transport into a cell
increases glucose transport into the cell by increasing its concentration gradient across the plasma membrane
the graph below shows the concentrations of B and C inside cells over time when the cell has imported B and C and is transferred to a solution containing a much lower concentration of B and C. based on these data, substance C is transported via
indirect active transport
Which part of the mitochondrion contains the proteins that carry out oxidative phosphorylation?
inner membrane (B)
When the difference in redox potential between two molecules is highly positive, what is true of the transfer of electrons between them?
it is highly favorable
Which of the following components of receptor-mediated endocytosis of LDL is incorrectly matched with its function?
lysosome: releases LDL from the receptor
brongkrekic acid is an antibiotic that inhibits the ATP/ADP transport protein in the inner mitochondrial membrane. which of the following will allow the electron transport to occur in mitochondria treated with bongkrekic acid?
making the inner membrane permeable to protons
Imagine you collected bacteria from the sediment in a frozen lake in Minnesota in January and compared the membranes to membranes from bacteria collected from a lake in Texas in June. Consider how the membranes would likely differ. The membranes in bacteria from the Minnesota lake would most likely have which of the following?
more unsaturated lipid tails than membranes in Texas bacteria
Which proteins bind to nuclear localization signals on newly synthesized proteins?
nuclear import receptors
Sodium ions, oxygen (O2), and glucose pass directly through lipid bilayers at dramatically different rates. Which of the following choices presents the correct order, from fastest to slowest?
oxygen, glucose, sodium ions
On what side of the plasma membrane are the carbohydrate chains of glycoproteins, proteoglycans, and glycolipids located?
the extracellular
If there is K+ channel in a plasma membrane and it opens for 100 milliseconds, which direction will K+ flow and why?
potassium ions will flow out of the cell through the ion channel down its concentration gradient.
When protons move down their electrochemical gradient into the mitochondrial matrix, what do they do?
produce ATP
The movement of electrons through the electron-transport chain in mitochondria does which of the following?
pumps protons out of the mitochondrial matrix
In cells that cannot carry out fermentation, which products derived from glycolysis will accumulate under anaerobic conditions?
pyruvate and NADH
In a typical human secretory cell, which of the following membranes has the largest surface area?
rough ER
the plasma membrane serves many functions, many of which depend on the presence of specialized membrane proteins. which of the following roles of the plasma membrane could still occur if the bilayer were lacking these proteins?
selective permeability
red blood cells have been very useful in the study of membranes and the protein components that provide structural support. Which of the following proteins is the principal fibrous protein in the cortex of the red blood cell?
spectrin
In eukaryotic cells, phospholipids are synthesized by enzymes bound to which of the following?
the cytosolic face of the endoplasmic reticulum
Multipass transmembrane proteins can form pores across the lipid bilayer. The structure of one such channel is shown in the diagram. In this figure, what do the areas shown in red represent?
the hydrophilic side chains of the transmembrane α helices
In a classic experiment designed to study nuclear transport, investigators added a dye molecule to the subunits of a protein called nucleoplasmin, which is involved in chromatin assembly. They then injected the intact protein or combinations of its subunits into the cytosol of a frog oocyte or into its nucleus. The results of the experiment are shown in the diagram, where redindicates the location of the labeled protein. Based on these results, which part of the nucleoplasmin protein bears a nuclear localization signal?
the tail only
How are newly made lipids supplied to the plasma membrane?
via the constitutive pathway of exocytosis
water moves across the plasma membrane into or out of a cell by osmosis when
water diffuses through a semipermeable membrane toward a higher solute concentration
In a lipid bilayer, where do lipids rapidly diffuse?
within the plane of their own monolayer
Three phospholipids X, Y, and Z are distributed in the plasma membrane as indicated below. For which of these phospholipids does a flippase probably exist?
x and y
