Chapter 9 – in mitochondrial electron transport, what is the direct role of o2?

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From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of glycolysis.

Drag each compound to the appropriate bin. If the compound is not involved in glycolysis, drag it to the “not input or output” bin.

Net Input: ADP, NAD⁺, Glucose

Net Output: ATP, NADH and Pyruvate,

not input or output: O₂, CO₂, coenzyme A and acetyl CoA

In acetyl CoA formation, the carbon-containing compound from glycolysis is oxidized to produce acetyl CoA. From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of acetyl CoA formation.

Drag each compound to the appropriate bin. If a compound is not involved in acetyl CoA formation, drag it to the “not input or output” bin. (Note that not all of the inputs and outputs of acetyl CoA formation are included.)

Net Input: NAD⁺, coenzyme A, pyruvate

Net Output: NADH, acetyl CoA, CO₂

not input or output: O₂, ADP, glucose and ATP

In the citric acid cycle (also known as the Krebs cycle), acetyl CoA is completely oxidized. From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of the citric acid cycle.

Drag each compound to the appropriate bin. If a compound is not involved in the citric acid cycle, drag it to the “not input or output” bin. (Note that not all of the inputs and outputs of the citric acid cycle are included.)

Net Input: Acetyl CoA, NAD⁺, ADP

Net Output: Coenzyme A, CO₂, NADH, ATP

Not Input or Output: Pyruvate, Glucose, O₂

In the last stage of cellular respiration, oxidative phosphorylation, all of the reduced electron carriers produced in the previous stages are oxidized by oxygen via the electron transport chain. The energy from this oxidation is stored in a form that is used by most other energy-requiring reactions in cells.
From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of oxidative phosphorylation.Drag each compound to the appropriate bin. If a compound is not involved in oxidative phosphorylation, drag it to the “not input or output” bin. (Note that not all of the inputs and outputs of oxidative phosphorylation are listed.)
Net Input: NADH, ADP, O₂
Net Output: NAD⁺, ATP, CO₂ and WaterNot Input or Output: Pyruvate, Glucose, Acetyl CoA, Coenzyme A and CO₂.

Cellular locations of the four stages of cellular respiration

Each of the four stages of cellular respiration occurs in a specific location inside or outside the mitochondria. These locations permit precise regulation and partitioning of cellular resources to optimize the utilization of cellular energy.

Glycolysis – Cytosol
Acetyl CoA – Mitochondrial matrix Citric acid cycle – Mitochondrial matrix
Oxidative phosphorylation – inner mitochondrial membrane

In glycolysis, as in all the stages of cellular respiration, the transfer of electrons from electron donors to electron acceptors plays a critical role in the overall conversion of the energy in foods to energy in ATP. These reactions involving electron transfers are known as oxidation-reduction, or redox, reactions.

Drag the words on the left to the appropriate blanks on the right to complete the sentences.

1) Oxidized
2) Reduced
3) Glucose
4) Pyruvate
5) NAD⁺
6) NADH

Energy from glycolysis

Among the products of glycolysis, which compounds contain energy that can be used by other biological reactions?

Pyruvate, NADH, ATP
ATP

TP synthesis in glycolysis: substrate-level phosphorylation

The ATP that is generated in glycolysis is produced by substrate-level phosphorylation, a very different mechanism than the one used to produce ATP during oxidative phosphorylation. Phosphorylation reactions involve the addition of a phosphate group to another molecule.

Sort the statements into the appropriate bin depending on whether or not they correctly describe some aspect of substrate-level phosphorylation in glycolysis.

Correct:
-One of the substrates is a molecule derived from the breakdown of glucose-An enzyme is required in order for the reaction to occur

-A bond must be broken between an organic molecule and phosphate before ATP can form.

Incorrect:
-The phosphate group added to ADP to make ATP comes from free inorganic phosphate ions.

-The enyzmes involved in ATP synthesis must be attached to a membrane to produce ATP.

In mitochondrial electron transport, what is the direct role of O2?
to function as the final electron acceptor in the electron transport chain

The effects of anaerobic conditions

How would anaerobic conditions (when no O2 is present) affect the rate of electron transport and ATP production during oxidative phosphorylation? (Note that you should not consider the effect on ATP synthesis in glycolysis or the citric acid cycle.)

Both electron transport and ATP synthesis would stop.

Comparing the amount of ATP synthesis from NADH and FADH2

NADH and FADH2 are both electron carriers that donate their electrons to the electron transport chain. The electrons ultimately reduce O2 to water in the final step of electron transport. However, the amount of ATP made by electrons from an NADH molecule is greater than the amount made by electrons from an FADH2 molecule.

Which statement best explains why more ATP is made per molecule of NADH than per molecule of FADH2?

Fewer protons are pumped across the inner mitochondrial membrane when FADH2 is the electron donor than when NADH is the electron donor

The effect of gramicidin on oxidative phosphorylation

When the protein gramicidin is integrated into a membrane, an H+ channel forms and the membrane becomes very permeable to protons (H+ ions). If gramicidin is added to an actively respiring muscle cell, how would it affect the rates of electron transport, proton pumping, and ATP synthesis in oxidative phosphorylation? (Assume that gramicidin does not affect the production of NADH and FADH2 during the early stages of cellular respiration.)

Sort the labels into the correct bin according to the effect that gramicidin would have on each process.

Remains the same: proton pumping rate, electron transport rate, rate of oxygen uptake
Decreases (or goes to zero): Rate of ATP synthesis, size of the proton gradient

The coupled stages of cellular respiration

The four stages of cellular respiration do not function independently. Instead, they are coupled together because one or more outputs from one stage functions as an input to another stage. The coupling works in both directions, as indicated by the arrows in the diagram below. In this activity, you will identify the compounds that couple the stages of cellular respiration.

Drag the labels on the left onto the diagram to identify the compounds that couple each stage. Labels may be used once, more than once, or not at all.

a. pyruvate
b. NADH
c. NAD+
d. NADH
e. NAD+

Anaerobic conditions and acetyl CoA formation

Under anaerobic conditions (a lack of oxygen), the conversion of pyruvate to acetyl CoA stops.

Which of these statements is the correct explanation for this observation?

In the absence of oxygen, electron transport stops. NADH is no longer converted to NAD+, which is needed for the first three stages of cellular respiration.

Cellular respiration and a cell’s demand for ATP

The rate of cellular respiration is regulated by its major product, ATP, via feedback inhibition. As the diagram shows, high levels of ATP inhibit phosphofructokinase (PFK), an early enzyme in glycolysis. As a result, the rate of cellular respiration, and thus ATP production, decreases. Feedback inhibition enables cells to adjust their rate of cellular respiration to match their demand for ATP.

Suppose that a cell’s demand for ATP suddenly exceeds its supply of ATP from cellular respiration.

Which statement correctly describes how this increased demand would lead to an increased rate of ATP production?

ATP levels would fall at first, decreasing the inhibition of PFK and increasing the rate of ATP production.

Fermentation – ATP production in the absence of oxygen

Under anaerobic conditions (a lack of oxygen), glycolysis continues in most cells despite the fact that oxidative phosphorylation stops, and its production of NAD+ (which is needed as an input to glycolysis) also stops. The diagram illustrates the process of fermentation, which is used by many cells in the absence of oxygen. In fermentation, the NADH produced by glycolysis is used to reduce the pyruvate produced by glycolysis to either lactate or ethanol. Fermentation results in a net production of 2 ATP per glucose molecule.

During strenuous exercise, anaerobic conditions can result if the cardiovascular system cannot supply oxygen fast enough to meet the demands of muscle cells. Assume that a muscle cell’s demand for ATP under anaerobic conditions remains the same as it was under aerobic conditions.

What would happen to the cell’s rate of glucose utilization?

Glucose utilization would increase a lot.

Carbon atoms in acetyl CoA formation and the citric acid cycle

During acetyl CoA formation and the citric acid cycle, all of the carbon atoms that enter cellular respiration in the glucose molecule are released in the form of CO2. Use this diagram to track the carbon-containing compounds that play a role in these two stages.

Drag the labels from the left (which represent numbers of carbon atoms) onto the diagram to identify the number of carbon atoms in each intermediate in acetyl CoA formation and the citric acid cycle. Labels may be used more than once.

A) 2 C
B) 6 C
C) 6 C
D) 5 C
E) 4 C
F) 4 C
G) 4 C
H) 4 C
I) 4 C

Net redox reaction in acetyl CoA formation and the citric acid cycle

In the sequential reactions of acetyl CoA formation and the citric acid cycle, pyruvate (the output from glycolysis) is completely oxidized, and the electrons produced from this oxidation are passed on to two types of electron acceptors.

Drag the labels on the left to show the net redox reaction in acetyl CoA formation and the citric acid cycle. Note that two types of electron carriers are involved.

a) CO2
(b) NADH
(c) FAD
(d)FADH2

Why is the citric acid cycle a cyclic pathway rather than a linear pathway?

In the oxidation of pyruvate to acetyl CoA, one carbon atom is released as CO2. However, the oxidation of the remaining two carbon atoms—in acetate—to CO2 requires a complex, eight-step pathway—the citric acid cycle. Consider four possible explanations for why the last two carbons in acetate are converted to CO2 in a complex cyclic pathway rather than through a simple, linear reaction.

Use your knowledge of the first three stages of cellular respiration to determine which explanation is correct.

It is easier to remove electrons and produce CO2 from compounds with three or more carbon atoms than from a two-carbon compound such as acetyl CoA.

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