Ch. 14 Smartwork Cell Bio

Which statements are true of the cytochrome c oxidase complex?

-It oxidizes cytochrome c. -It acts as a proton pump. -It reduces molecular oxygen.

Which is true of the carbon-fixation (Calvin) cycle?

-It requires NADPH and ATP. -It regenerates energy-rich ribulose 1,5-bisphosphate. -It requires energy-rich ribulose 1,5-bisphosphate -It requires CO2.

Which of the following statements are true of electron transfer in the electron-transport chain?

-NADH is a strong electron donor. -Electrons move toward molecules with a high redox potential. -Each electron transfer is an oxidation-reduction reaction.

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.

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

What is true of the antenna complex of a photosystem?

It captures light energy.

The electron-transport chain in mitochondria accepts high-energy electrons directly from which molecule?

NADH

Most of the energy for the synthesis of ATP comes from which molecule?

NADH produced by the citric acid cycle

What is one reason that plants do not generally produce sugars after dark?

The enzymes involved in stage 2 of photosynthesis are inactivated in the dark.

During stage I of photosynthesis, excited electrons move in which direction?

from the chlorophyll special pair to an electron carrier to NADP+

It is energetically favorable for protons to flow in which direction?

from the intermembrane space to the mitochondrial matrix

The electron-transport chain pumps protons in which direction?

from the matrix to the intermembrane space

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 low redox potential of NADH means that it has a

tendency to give up electrons.

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.

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.

The electrochemical proton gradient across the mitochondrial membrane can be used to drive which processes?

-import of ADP into the mitochondrial matrix -export of ATP from the mitochondrial matrix -import of pyruvate into the mitochondrial matrix

Several genetic diseases are caused by mutations in mitochondrial DNA. In some countries, a technique known as mitochondrial replacement therapy is being used to allow couples to conceive healthy children. What is the basic procedure in this technique?

A nucleus from an egg with faulty mitochondria is placed into an enucleated donor egg.

Carbon fixation occurs in the second stage of photosynthesis, during the light-independent reactions of the Calvin cycle. In the first step of this cycle, the enzyme Rubisco adds CO2 to the energy-rich compound ribulose 1,5-bisphosphate, ultimately producing two molecules of 3-phosphoglycerate. 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?

Ribulose 1,5-bisphosphate would be depleted, but 3-phosphoglycerate would accumulate.

As the human population grows, it becomes increasingly important to maximize crop yields. As such, scientists search for more efficient ways for plants to convert CO2 into biomass. One approach is to genetically modify plant enzymes involved in photosynthesis to increase their efficiency. Which plant enzyme, directly responsible for carbon fixation, is a focus of research?

Rubisco

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.

During electron transport, which serves as a ready source for protons that can be pumped across the membrane?

H2O

Which of the following statements correctly describe an aspect of converting light to chemical energy in chloroplasts?

-Excited electrons are passed through an electron transport chain. -The energy in excited electrons is used to pump protons across the thylakoid membrane from the stroma to the thylakoid space.

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 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. -The mitochondria use the proton gradient to synthesize ATP.

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?

-conformational changes of the F1 ATPase -movement of protons down their gradient through ATP synthase -rotation of the rotor in the membrane

Which of these processes require a membrane?

-generation of ATP by photosynthesis in bacteria -generation of energy by mitochondria -generation of ATP by photosynthesis in plants -generation of ATP by oxidative phosphorylation

Which of the following organisms have mitochondria in their cells?

-protozoa -plants -yeasts -animals

For every three molecules of CO2 that enter the carbon-fixation cycle, what is produced and what is consumed?

1 molecule of glyceraldehyde 3-phosphate is produced, and 9 molecules of ATP + 6 molecules of NADPH are consumed.

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.

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

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.

During oxidative phosphorylation, why does a single molecule of NADH result in the production of more ATP molecules than a single molecule of FADH2?

FADH2 and NADH feed their electrons to different carriers in the electron-transport chain.

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. In each vesicle, the proton pump is oriented such that it will pump H+ into the vesicle. But the ATP synthase molecules are randomly inserted: half the vesicles will have an ATP synthase that faces inward, and half will have an ATP synthase that faces outward. When ADP and Pi are added to the external medium and the vesicles are exposed to light, what will happen?

Half of the ATP synthase molecules will produce ATP, and the other half will do nothing.

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 the process of combining CO2 and H2O to make a carbohydrate?

It is energetically unfavorable

What would be the consequences to NADPH production if the redox potential of pC (plastocyanin) were altered to be more negative than the redox potential of cytochrome b6-f?

NADPH production would halt since pC would no longer accept electrons from the cytochrome b6-f complex, blocking the electron transport chain.

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.

Some types of bacteria can survive under both aerobic and anaerobic conditions. Regardless of whether oxygen is present, these cells maintain a proton gradient across the plasma membrane to drive ATP synthesis and the import of nutrients. Under aerobic conditions, an H+ gradient across the plasma membrane is produced by the transfer of electrons along the respiratory chain. When oxygen is present, what would be expected to occur in the plasma membrane of these bacteria?

Protons flow into the bacterial cell through ATP synthase, generating ATP.

Why does cytochrome c oxidase bind to oxygen very tightly?

Release of partially reduced oxygen radicals can damage the cell.

During photosynthesis, charge separation takes place when which of the following occurs?

The special pair passes an electron to an electron carrier in the reaction center, leaving behind a positive charge.

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