Cellular Energetics Quiz

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Questions and Answers

___ is the carbon-containing compound produced by glycolysis.

CO2

Acetyl CoA

Pyruvate (correct)

Glucose

In the glycolytic pathway, which of the following are allosterically controlled enzymes?

triose phosphate isomerase

phosphofructokinase-1 (correct)

enolase

none of the above

Yeasts use fermentation to synthesize ATP:

because yeasts lack mitochondria.

to produce lactic acid.

because fermentation produces more ATP than oxidative phosphorylation.

in the absence of oxygen. (correct)

In the overall reaction for cellular respiration, glucose is:

oxidized to CO2. Signup and view all the answers

Phosphofructokinase is active in the glycolytic pathway when the levels of ATP are high in cell because .

less; ATP is an allosteric inhibitor Signup and view all the answers

In the absence of oxygen, NAD+ is recovered by , which leads to a net production of ATP molecules for each glucose molecule broken down.

fermentation; two Signup and view all the answers

Which of the following is FALSE regarding mitochondrial structure?

The outer mitochondrial membrane contacts the cellular cytosol and the mitochondrial matrix. Signup and view all the answers

Which of the following health-related conditions are NOT related to mitochondrial function?

Tay-Sachs disease Signup and view all the answers

Electron transport from NADH and FADH2 to O2 occurs in the:

mitochondrial inner membrane. Signup and view all the answers

Compared with glucose, oxidation of which of the following is more important in humans as a source of ATP?

fats Signup and view all the answers

The four stages of glucose oxidation are listed below. Place them in the correct order. I. pyruvate oxidation to CO2 in the mitochondrion via a 2-carbon acetyl CoA intermediate (citric acid cycle) II. electron transport to generate a proton motive force III. conversion in the cytosol of one 6-carbon glucose molecule to two 3-carbon pyruvate molecules (pyruvate) (glycolysis) IV. ATP synthesis in the mitochondrion (oxidative phosphorylation)

III, I, II, IV Signup and view all the answers

The molecule that immediately enters the citric acid cycle is formed by which process?

pyruvate conversion Signup and view all the answers

The first step in the citric acid cycle occurs when acetyl CoA reacts with oxaloacetate to form:

citrate Signup and view all the answers

Glucose is not the only energy-containing molecule that can enter cellular respiration pathways. Which food source is most likely to enter the citric acid cycle as fatty acids?

fats Signup and view all the answers

NADH-COQ reductase and CoQH2-cytochrome c reductase each use the energy derived from electron transfer to transport ____ the mitochondrial matrix.

four protons into Signup and view all the answers

___ is a lipid soluble molecule that acts to shuttle electrons within the mitochondrial inner membrane.

CoQ Signup and view all the answers

In mitochondria, the proton-motive force is due largely to:

a voltage gradient across the inner membrane. Signup and view all the answers

During cellular respiration, the electron transport chain utilizes the energy produced from passing electrons from one molecule to the next to create:

a proton gradient. Signup and view all the answers

Which of the following statement(s) regarding the origin of the mitochondria is(are) TRUE?

A bacterium invaded and established a symbiotic relationship with a eukaryotic host cell. Signup and view all the answers

During ATP synthesis, protons move “down” their electrochemical gradient through:

the Fo complex of ATP synthase Signup and view all the answers

Transport of pyruvate into the mitochondrial matrix depends on energy provided by:

the proton-motive force. Signup and view all the answers

Brown-fat mitochondria uncouple oxidative phosphorylation to produce:

heat. Signup and view all the answers

A major source of reactive oxygen species (ROS) in animal cells is:

electron transport in the mitochondria. Signup and view all the answers

In chloroplasts, light absorption, electron transport, and ATP synthesis all occur:

in or on the thylakoid membrane. Signup and view all the answers

The principal pigment involved in photosynthesis is:

chlorophyll a. Signup and view all the answers

In photosynthesis, all of the following reactions are directly dependent on light, except:

carbon fixation. Signup and view all the answers

Based on what you know about the action spectra of photosynthesis, irradiating a leaf with which of the following light types would result in the release of the greatest quantities of oxygen?

red and blue light Signup and view all the answers

The "tail" of chlorophyll is hydrophobic, which is important for:

anchoring it in the thylakoid membrane. Signup and view all the answers

Plastoquinone, like ubiquinone, can move freely within the membrane. This is important for its function as:

an electron and proton shuttle. Signup and view all the answers

What is the role of water in the light reactions of photosynthesis?

source of electrons Signup and view all the answers

Early investigators thought the oxygen produced by photosynthetic plants came from carbon dioxide. In fact, it comes from:

water. Signup and view all the answers

Cyclic electron flow in the thylakoid membrane generates:

a proton-motive force. Signup and view all the answers

During photosynthesis, O2 is produced:

on the luminal face of the thylakoid membrane. Signup and view all the answers

During cyclic electron flow, electron transport:

takes place only in PSI. Signup and view all the answers

All of the following statements describe the process of photorespiration, except:

photorespiration generates substantial amounts of ATP. Signup and view all the answers

The enzymes that catalyze the Calvin cycle are found in the:

stromal space. Signup and view all the answers

The fixation of CO2 into carbohydrates is catalyzed by:

ribulose 1,5-bisphosphate carboxylase. Signup and view all the answers

Plants use ____ to transport sucrose to all regions of the organism.

the phloem Signup and view all the answers

Why doesn't the Calvin cycle end after a three-carbon sugar is produced?

because RuBP must be generated for the cycle to continue Signup and view all the answers

The Calvin cycle:

uses electrons from NADPH and ATP to produce glucose. Signup and view all the answers

What is the role of substrate-level phosphorylation in glycolysis?

During glycolysis, substrate level phosphorylation is used to synthesize ATP. This process occurs twice during glycolysis and involves the transfer of a high-energy phosphate group (from 1,3-bisphosphate or phosphoenolpyruvate) to ADP. Signup and view all the answers

During prolonged exercise, oxygen is scarce in muscle tissue. Under these conditions, muscle cells convert pyruvate to two molecules of lactic acid. What happens to the lactic acid that is generated in this way?

Lactic acid is secreted from muscle cells into the bloodstream. Some is taken up from the bloodstream by the liver, where it is either reoxidized to pyruvate then metabolized to generate energy and CO2 or it is converted back to glucose and stored as glycogen in the liver. Some of the lactic acid is metabolized to CO2 in the heart. Signup and view all the answers

What is the function of the malate–aspartate shuttle?

The malate–aspartate shuttle functions to deliver the electrons produced during glycolysis and carried by cytosolic NADH across the mitochondrial inner membrane to the matrix, where the electrons serve to reduce NAD+ to NADH in the matrix. This NADH in the matrix can then donate electrons to the electron transport chain. Signup and view all the answers

What molecule acts as an electron donor during photosynthesis in chloroplasts? What alternative is used by some photosynthetic bacteria (e.g., purple bacteria)?

H2O is the electron donor during photosynthesis in chloroplasts, whereas some photosynthetic bacteria (e.g., purple bacteria) can use H2S or H2 as an electron donor. Signup and view all the answers

Which components of PSII are responsible for producing the proton-motive force?

Several components of PSII contribute to the proton-motive force, albeit by different mechanisms. First, the removal of electrons from water by P680 generates protons in the thylakoid space. Next, the delivery of electrons by quinone Q to cytochrome bf is accompanied by the transfer of two protons from the stroma to the thylakoid lumen. Finally, protons may be transported from the stroma to the thylakoid space by cytochrome bf functioning in a Q cycle. Signup and view all the answers

ATP synthase is composed of two oligomeric proteins, F0 and F1. What is the function of each protein complex and where is each found in mitochondria?

F0 is a proton-channel protein and the F1 complex is an ATPase running in reverse. F0 is found in the mitochondrial inner membrane and F1 is associated with F0 on the matrix face of the inner membrane. Signup and view all the answers

What is the source of the energy for carbon fixation?

The reactions that fix CO2 are powered by energy released by ATP hydrolysis and by the reducing agent NADPH. The ATP and NADPH were previously generated from the energy of absorbed photons of light. Signup and view all the answers

What is photorespiration? How is it related to photosynthesis?

Photorespiration competes with the process of photosynthesis. During photorespiration, O2 and ATP are consumed and CO2 is generated. Rubisco, which acts to fix CO2, also catalyzes photorespiration. Photorespiration is favored when stomata close to prevent moisture loss, and CO2 levels inside the leaf fall below the Km of rubisco for CO2. Signup and view all the answers

Explain how the rates of photosynthesis in plants like corn and sugarcane can be two to three times faster than the rates of photosynthesis in plants like wheat or rice.

Sugarcane and corn are C4 plants, whereas wheat and rice are C3 plants. C4 plants have evolved a two-step system that reduces the rate of photorespiration and enhances the rate of photosynthesis. This system works via a CO2 shuttle that involves binding CO2 in mesophyll cells. The carbon dioxide is stored in the oxaloacetate. Oxaloacetate is a four-carbon molecule that gives the C4 plants their name. Oxaloacetate is converted to malate, which is transferred to bundle cells. Malate reacts to release CO2 in the bundle cells. This increases the CO2 concentration in bundle cells and, as a result, increases the rate of photosynthesis. Signup and view all the answers

Which stages of photosynthesis can occur only in the light and which can also occur in the dark?

Of the four stages of photosynthesis, the first three (light absorption, electron transport, and ATP synthesis) can occur only when light is available. The last stage, carbon fixation, can occur whether or not light is available. Although carbon fixation can take place in the dark, the reactions involved are often turned off in the dark to conserve ATP for other cellular processes. Signup and view all the answers

What is the role of quinone in generating the charge separation needed to remove electrons from H2O for use in electron transport?

Quinone Q is a strong reducing agent and accepts an electron from reaction-center chlorophyll when this chlorophyll is in a photon-induced excited state. This leaves the reaction-center chlorophyll in a strong oxidizing state that is powerful enough to remove electrons from H2O. Signup and view all the answers

Each cytochrome in the electron transport chain has a different reduction potential. What is the importance of these differences for electron transport?

The different reduction potential (or tendency to accept an electron) of the cytochromes in the electron transport chain allows these molecules to establish a unidirectional electron flow along the chain. Signup and view all the answers

Study Notes