Chapter 14

Which of the following organisms do not have mitochondria in their cells?

Bacteria

Which of the following statements is true about 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.

Mobile electron carriers feed electrons into the electron-transport chain.

False

Which of these processes does NOT involve a membrane?

Generation of ATP by glycolysis

Which of the following is not a direct source of fuel for mitochondria?

Glucose

In the electron-transport chain, what provides the main reservoir for protons that are pumped across the membrane?

H2O

What is the ratio of ATP and ADP concentrations in the cytosol of a cell?

High ATP/ADP ratio

When the difference in redox potential between two molecules is highly positive, the transfer of electrons between them is:

highly favorable

In mitochondria, what is the final electron acceptor in the electron-transport chain?

Molecular oxygen (O2)

The electron-transport chain in mitochondria accepts high-energy electrons directly from:

NADH and FADH2.

Iron-sulfur clusters tend to have a relatively low affinity for electrons. Which component of the electron-transport chain most likely contains an iron-sulfur cluster?

NADH dehydrogenase complex

Which of the following is true?

NADH has a weak affinity for electrons and a negative redox potential.

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.

What occurs when ATP synthase operates "in reverse" and pumps H+ across a membrane against its electrochemical proton gradient?

The ATP synthase hydrolyzes ATP to form ADP and Pi.

The organelles that produce ATP in eukaryotic animal cells:

evolved from bacteria engulfed by ancestral cells billions of years ago.

It is energetically favorable for protons to flow:

from the intermembrane space to the mitochondrial matrix.

The electron-transport chain pumps protons:

from the matrix to the intermembrane space.

The energy efficiency of cell respiration:

is more than that of a gasoline-powered engine.

When protons move down their electrochemical gradient into the mitochondrial matrix, they:

produce ATP.

In the electron-transport chain, as electrons move along a series of carriers, they release energy that is used to:

pump protons across a membrane

The movement of electrons through the electron-transport chain in mitochondria:

pumps protons out of the matrix

When O2 accepts electrons in the electron-transport chain, O2 becomes:

reduced

The electrochemical proton gradient can drive the active transport of metabolites into and out of the mitochondrial matrix.

True

The outer membrane of a mitochondrion is permeable to all small molecules, including small proteins.

True

To move a proton from one side of a membrane to the other, an electron carrier must be oriented in such a way that it accepts an electron (along with a H+ from water) on one side of the membrane and then releases the H+ on the other side of the membrane as it passes the electron to the next carrier

True

In mitochondria, about how many molecules of ATP can be produced from the complete oxidation of a single glucose molecule?

30

In this cartoon representation of the structure of ATP synthase, which of the components catalyzes the synthesis of ATP?

4

Which of the following drives the production of ATP from ADP and Pi by ATP synthase?

A proton gradient

What is the main chemical energy currency in cells?

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.

ATP export will decrease because its carrier exploits the difference in voltage across the inner membrane

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

1 and 5

In an animal cell, where are the proteins of the electron-transport chain located?

In the mitochondrial inner membrane

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, and the DNP-treated vesicles are exposed to light, will ATP be produced?

No. 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, a H+ gradient across the plasma membrane is produced by the transfer of electrons along the respiratory chain. When oxygen is present, what do you think takes place in the plasma membrane of these bacteria?

Protons flow into the bacterium through ATP synthase, generating ATP.

Which of the following is NOT true of mitochondria?

They are replaced by chloroplasts in plants.

Each of the three respiratory enzyme complexes includes metal atoms that are tightly bound to the proteins.

True

Mitochondria can change their location, shape, and number in the cell to suit the needs of a cell

True

Which of the following statements is NOT true of electron transfer in the electron-transport chain?

When an electron carrier accepts an electron, it becomes oxidized.

To explore how yeast cells metabolize glucose, investigators examine the effect the sugar has on the expression of a variety of genes using a DNA microarray. 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 glucose has increased the expression of the genes, whereas green indicates that glucose has decreased gene expression. Based on these 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.

As electrons move through the electron-transport chain, they are passed from:

a carrier molecule of lower electron affinity to a carrier molecule of higher electron affinity.

ATP synthase:

can either produce or break down ATP depending on the magnitude of the electrochemical proton gradient

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 will donate electrons to the electron-transport chain, thereby reducing the electron carriers in the chain almost completely. When oxygen is then introduced, the carriers become oxidized at different rates, as shown by the colored curves in the figure. Based on the rates of oxidation, in what direction do electrons pass along the electron-transport chain? (For simplicity, the carriers are represented by the numbers 1-4.)

succinate → 1 → 2 → 3 → 4 → O2

Ubiquinone has a redox potential of +30 mV, while cytochrome c has a redox potential of +230 mV. In the electron-transport chain, electrons flow from:

ubiquinone to cytochrome c