BIOL EXAM 2

Shown is a schematic diagram of a membrane phospholipid. Which segment will always carry a negative charge?

B

Which molecules are required for the citric acid cycle to fully oxidize the carbons donated by acetyl CoA?

- oxaloacetate - NAD+ - O2 - GDP

In the patch-clamp technique (shown here), a small glass electrode forms a tight seal with a portion of the cell membrane (A), allowing detection of ion flow through channels (B). This technique has clinical uses. For example, some individuals with high blood pressure (hypertension) have a genetic defect in an epithelial Na+ channel (ENaC) that makes the channel hyperactive (open more than normal). Such individuals can be treated with amiloride, which inhibits sodium ion movement through ENaC. Researchers predicted that amiloride would not effectively treat hypertension in individuals with normal ENaC activity and tested this prediction by analyzing ENaC activity in patch-clamped cells from individuals with high blood pressure, some of whom showed hyperactive ENaC and some of whom showed normal ENaC activity. Which of the following results align with researcher expectations?

-Patch-clamp data showed hyperactive ENaC prior to amiloride treatment; patient benefited from amiloride. -Patch-clamp data showed normal ENaC activity prior to amiloride treatment; patient did not benefit from amiloride.

Why must all living cells carefully regulate the fluidity of their membranes?

-to allow membranes, under appropriate conditions, to fuse with one another and mix their molecules -to ensure that membrane molecules are distributed evenly between daughter cells when a cell divides -to permit membrane lipids and proteins to diffuse from their site of synthesis to other regions of the cell

In this illustration of the structure of ATP synthase, which of the components rotate?

1 & 5

Investigators purify mitochondria from mammalian liver cells. They incubate these mitochondria in the absence of oxygen and the presence of succinate, an intermediate produced during the citric acid cycle.Under these conditions, succinate can donate electrons to the electron-transport chain, thereby reducing the electron carriers in the chain almost completely.When oxygen is re-introduced to this preparation, the carriers will become oxidized at different rates, as shown by the colored curves in the figure.Based on these oxidation curves, place the listed components in the order in which electrons would be passed from one to the next along the electron-transport chain. (For simplicity, the carriers are represented by the numbers 1-4.)

1 (electron donor). succinate 2. 1 3. 2 4. 3 5. 4 6 (electron acceptor). O2

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

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. A. NaCl, because Na+ is needed for glucose entry. B. HCl, because H+ is needed for glucose entry. C. KCl, because Cl- is needed for glucose entry. D. KCl, because K+ is needed for glucose entry.

A. NaCl, because Na+ is needed for glucose entry.

Which of the following describes the resting membrane potential of a neuron? A. a state in which the flow of positive and negative ions across the plasma membrane is precisely balanced B. a voltage difference across the plasma membrane when the neuron has been stimulated C. a voltage difference across the plasma membrane, with more positive membrane potential inside D. a voltage difference of 0 millivolts (mV) across the membrane E. a voltage difference that is chiefly a reflection of the electrochemical Na+ gradient across the plasma membrane

A. a state in which the flow of positive and negative ions across the plasma membrane is precisely balanced

You join a laboratory to study muscle function. You decide to inhibit the pumping of Ca2+ into the sarcoplasmic reticulum to determine how excess cytosolic Ca2+ will affect muscle function. Which of the following strategies would be effective in blocking Ca2+ pumping? A. block the phosphorylation of the conserved aspartate in the Ca2+ pump B. block binding of ATP to the pump in the lumen of the sarcoplasmic reticulum C. enhance the binding of ATP to the Ca2+ pump D. block the hydrolysis of ATP to AMP by the Ca2+ pump

A. block the phosphorylation of the conserved aspartate in the Ca2+ pump

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? A.The NADH dehydrogenase, cytochrome b-c1, and cytochrome oxidase complexes all pump protons across the membrane. B.The pH inside the mitochondrial matrix is higher than in the intermembrane space. C.The mitochondria use the proton gradient to synthesize ATP. D.Protons are pumped into the matrix of the mitochondria.

A.The NADH dehydrogenase, cytochrome b-c1, and cytochrome oxidase complexes all pump protons across the membrane. B.The pH inside the mitochondrial matrix is higher than in the intermembrane space. C.The mitochondria use the proton gradient to synthesize ATP.

The main regulatory step of glycolysis occurs in step 3. Choose all of the following that correctly describe some aspect of step 3 in glycolysis.

A.The enzyme that catalyzes step 3 is phosphofructokinase. B.The reaction is an irreversible reaction. C.The reaction generates the product fructose 1,6-bisphosphate. D.The enzyme uses an 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 statements below accurately describe an aspect of the citric acid cycle? A.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. D.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.

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.

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.

In a patch of animal cell membrane about 10 μm in area, which will be true? A. There will be more carbohydrates than lipids. B. There will be more proteins than lipids. C. There will be about an equal number of proteins and lipids. D. There will be more lipids than proteins. E. Because the lipid bilayer acts as a two-dimensional fluid, there is no way to predict the relative numbers of proteins and lipids in any patch of cell membrane.

D. There will be more lipids than proteins. Proteins constitute about half the mass of an animal cell membrane. Therefore, in terms of mass, proteins and lipids provide an equal share. However, lipids are much smaller than proteins, so a cell membrane typically contains 50 times more lipid molecules than protein molecules.Carbohydrates are only present on a subset of proteins (glycoproteins) and lipids (glycolipids). Thus, they contribute a relatively small amount to the mass of a cell membrane.

When ATP and food molecules such as fatty acids are abundant, which will occur?

Enzymes involved in gluconeogenesis will use energy to produce glucose.

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.

Experiments performed by Hans Krebs in the 1930s revealed that the set of reactions that oxidize food molecules and produce CO2 occur in a cycle. In one experiment, Krebs exposed pigeon muscles to malonate, a compound that inhibits succinate dehydrogenase—the enzyme that converts succinate to fumarate, indicated in red in the linear representation of the reactions of the citric acid cycle (below). Which of the following observations, made in malonate-treated muscle, led Krebs to believe that this set of reactions is cyclical?

If fumarate were added, succinate would accumulate.

Which statement is true of glycogen phosphorylase? A. It is activated by glucose 6-phosphate and by ATP. B. It is activated by glucose 6-phosphate, but inhibited by ATP. C. It is inhibited by glucose 6-phosphate and by ATP. D. It is inhibited by glucose 6-phosphate, but activated by ATP. E. It stimulates gluconeogenesis.

It is inhibited by glucose 6-phosphate and by ATP

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.

To study the structure of a particular membrane protein, the target protein is usually removed from the membrane and separated from other membrane proteins. Shown below are three different proteins associated with the cell membrane. Treatment with high salt would release which protein or proteins from the bilayer?

See image.

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

In the technique called optogenetics, light-gated Na+ channels are introduced into the brains of living animals. Activation of these channels by light can depolarize the membranes of neurons that contain them, selectively activating these target cells.Since its inception, optogenetics has been expanded to include other types of light-gated channels, such as a channel that is selective for Cl- instead of Na+. If this light-gated Cl- channel were introduced into neurons in a region of the brain that stimulates feeding, what might you expect to see?

The animals would avoid eating, even when they are hungry—but only when the channels are activated by light.

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.

In 1925, scientists exploring how lipids are arranged within cell membranes performed a key experiment using red blood cells. Using benzene, they extracted the lipids from a purified sample of red blood cells. Because these cells have no nucleus and no internal membranes, any lipids they obtained were guaranteed to come from the plasma membrane alone.The extracted lipids were floated on the surface of a trough filled with water, where they formed a thin film. Using a movable barrier, the researchers then pushed the lipids together until the lipids formed a continuous sheet only one molecule thick.The researchers then made an observation that led them to conclude that the plasma membrane is a lipid bilayer.Which of the following would have allowed the scientists to come to this conclusion?

The extracted lipids covered twice the surface area of the intact red blood cells.

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.

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.

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?

They will accumulate fats because cells can convert glycolytic metabolites into lipids.

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 membrane would show a more rapid recovery of fluorescence in a FRAP study?

a membrane containing a larger proportion of unsaturated fatty acids

After an overnight fast, most of the acetyl CoA entering the citric acid cycle is derived from what type of molecule?

fatty acids

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

If acetyl CoA labeled with radioactive 14C in both carbon positions were fed into the citric acid cycle, where would the radioactivity be after two turns of the cycle?

in oxaloacetate and in CO2

In an electron transport chain, electrons are passed from one transmembrane electron carrier to another, driving proton movement across a membrane (see image below). The protons then flow through ATP synthase (not shown) to generate ATP. In a 2018 article (Budin, et al., Science vol. 362) researchers probed how membrane fluidity affects electron transport chain activity and ATP production in E. coli by manipulating membrane fluidity and measuring respiration. How could researchers have increased membrane fluidity?

increase the proportion of phospholipids with unsaturated fatty acids

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

A group of researchers wanted to sort different white blood cell types (monocytes, lymphocytes, and granulocytes) apart from each other based on size differences and to remove unwanted contaminating red blood cells. After a particular manipulation, the red blood cells lysed. The remaining white blood cells increased in size and, more importantly, the size differences among cells increased, allowing for size-based sorting (which requires minimum size differences among cells). What manipulation did the researchers use to increase cell size?

placing cells in an environment with a lower solute concentration than that in the cells

In cells that cannot carry out fermentation, which products derived from glycolysis will accumulate under anaerobic conditions?

pyruvate and NADH

Glycolysis occurs in a series of 10 steps using 10 different enzymes. Place the following broad events that occur during glycolysis into their correct order.

see image

Order these components involved in electron transport from those with the lowest redox potential to the highest.

see image

The P-type ATPase Ca2+ pump transports Ca2+ ions into the sarcoplasmic reticulum in muscle cells in a series of steps. Put the following steps into the correct order.

see image for answer

Your friend is attempting to study the function of the Na+-K+ pump and has created spherical liposomes that contain only the Na+-K+ pump. She has inserted the pumps so that the extracellular side of the pump is also outside the liposome. She has added different ions and energy sources to the beaker with the liposomes, but no pumping of ions occurs. You explain that components must be in the proper location inside or outside the liposome for the pump to work. Help her by adding the proper components to the inside or outside of the liposome so that proper pumping occurs. Place unneeded components in the unneeded box.

see image for answer

In the absence of oxygen, in cells that cannot carry out fermentation, glycolysis would halt at which step?

the oxidation of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate