Question 1

Which carbon atom(s)of pyruvate is(are)first converted to carbon dioxide by pyruvate dehydrogenase complex?

Accepted Answer

The carboxylate carbon (#1) of pyruvate is first converted to carbon dioxide by the pyruvate dehydrogenase complex. This is part of the process where pyruvate is converted into acetyl-CoA, with the decarboxylation step removing the carboxylate group as CO2.

Question 2

Pyruvate passes through the outer mitochondrial membrane by ________.

Accepted Answer

Porin proteins, located in the outer mitochondrial membrane, allow molecules such as pyruvate to pass through by facilitating their transport across the membrane.

Question 3

Which is not a component of the pyruvate dehydrogenase complex?

Accepted Answer

Isocitrate dehydrogenase is not a component of the pyruvate dehydrogenase complex. The three components of the complex are dihydrolipoamide dehydrogenase, pyruvate dehydrogenase, and dihydrolipoamide acetyltransferase.

Question 4

Pyruvate translocase is a(n)________ protein that transports ________.

Accepted Answer

Pyruvate translocase is a symport protein that transports pyruvate and H⁺ ions together into the mitochondria.

Question 5

What are the fewest number of turns of the citric acid cycle needed before carbon radioactive in both carbons of the acetyl group in acetyl Co A are incorporated into all 4 carbons in every molecule of oxaloacetate produced?

Accepted Answer

The answer of What are the fewest number of turns...

Question 6

When energy-rich acetyl CoA is oxidized to carbon dioxide,eight electrons are released.Most often,electrons are released in such reactions because

Accepted Answer

The answer of When energy-rich acetyl CoA is oxidized to...

Question 7

Pyruvate dehydrogenase kinase catalyzes

Accepted Answer

Pyruvate dehydrogenase kinase phosphorylates and inactivates E1 of the pyruvate dehydrogenase complex.

Question 8

The pyruvate dehydrogenase complex is larger than a ribosome.In bacteria these complexes are located in the cytosol while they are found in ________ of eukaryotes

Accepted Answer

The pyruvate dehydrogenase complex is found in the mitochondrial matrix of eukaryotes, where it plays a crucial role in linking glycolysis, which occurs in the cytosol, with the citric acid cycle by converting pyruvate into acetyl-CoA.

Question 9

The order of prosthetic groups as they act in the three proteins of the PDH(pyruvate dehydrogenase)complex is:

Accepted Answer

The correct order of prosthetic groups as they act in the PDH complex is thiamine pyrophosphate (TPP) → dihydrolipoamide (DHLA) → FAD. TPP is responsible for decarboxylation of pyruvate, which yields a hydroxyethyl-TPP intermediate. The hydroxyethyl group is then transferred to the DHLA moiety of the dihydrolipoamide acetyltransferase (E2) subunit. The resulting acetyl-DHLA is then oxidized by FAD, which is located on the dihydrolipoamide dehydrogenase (E3) subunit. Finally, the electrons from FADH2 are transferred to NAD+ to form NADH, which is then used by the cell for ATP production. Therefore, option C is the best choice as it correctly lists the order of prosthetic groups in the PDH complex.

Question 10

The enzyme pyruvate translocase is located ________.

Accepted Answer

Pyruvate translocase is located in the inner mitochondrial membrane. It transports pyruvate from the cytosol to the mitochondrial matrix for further metabolism.

Question 11

Some bacteria and anaerobic eukaryotes not using PDH(pyruvate dehydrogenase)form acetyl CoA and CO₂ from pyruvate with ________.

Accepted Answer

Bacteria and anaerobic eukaryotes that do not use PDH to form acetyl CoA and CO₂ from pyruvate can use pyruvate:ferredoxin oxidoreductase. This enzyme catalyzes the conversion of pyruvate to acetyl-CoA, CO2, and reduced ferredoxin. This process replaces the role of PDH in these organisms.

Question 12

The citric acid cycle oxidizes pyruvate,and some of the pathway intermediates are starting materials for many biosynthetic pathways.This means that the citric acid cycle is ________.

Accepted Answer

The citric acid cycle is amphibolic, which means it is both catabolic (breaking down molecules to release energy) and anabolic (using energy to build molecules). It breaks down pyruvate (catabolic), while also providing intermediates for biosynthesis (anabolic).

Question 13

Most of the energy released in citric acid cycle reactions is conserved in ________.

Accepted Answer

The majority of the energy released in the citric acid cycle reactions is conserved in NADH and QH². These high-energy molecules are then used to produce ATP through oxidative phosphorylation in the electron transport chain. While a small amount of ATP is also directly produced in the citric acid cycle through substrate-level phosphorylation, it is not the main source of energy conservation. GTP and ADP are also produced in the cycle, but they are not the main energy carriers.

Question 14

The arrangement of subunits in the PDH(pyruvate dehydrogenase)complex ensures that ________.

Accepted Answer

The arrangement of subunits in the PDH complex ensures that the product of one enzyme is delivered to the next in turn. This helps to coordinate the series of reactions and prevent the escape of intermediates from the complex. ATP is not directly formed by the PDH complex, although it does play a crucial role in aerobic respiration overall. The dihydrolipoamide arm can react with NAD+ as part of the complex, but this is not the main function of the arrangement of subunits. Acetyl CoA does enter into the series of reactions, but this is facilitated by the overall architecture of the complex and not necessarily the specific arrangement of subunits.

Question 15

Which cofactor is not used by the pyruvate dehydrogenase complex?

Accepted Answer

QH₂ is not a known cofactor, therefore it is not used by the pyruvate dehydrogenase complex. The other three cofactors (lipoamide, thiamine pyrophosphate, and FAD) are all known to be used by the pyruvate dehydrogenase complex.

Question 16

The net effect of the eight steps of the citric acid cycle is to

Accepted Answer

The eight steps of the citric acid cycle completely oxidize an acetyl group, which is derived from pyruvate or fatty acids, to carbon dioxide. This process generates energy in the form of ATP, NADH, and FADH2. The cycle does not convert pyruvate to succinate, nor does it produce 8 ATP for every pass through the cycle. While NAD+ and Q are involved in the cycle, their production is not the net effect of the cycle.

Question 17

A deficiency in thiamine causes the disease beriberi.Which might you expect to have a higher than normal blood concentration in an individual with this condition?

Accepted Answer

Thiamine is required for the conversion of pyruvate to acetyl CoA via the pyruvate dehydrogenase complex. A deficiency in thiamine would result in impairment of this process, leading to an accumulation of pyruvate. Thus, an individual with beriberi may have a higher than normal blood concentration of pyruvate.

Question 18

Compounds like succinate,fumarate and α-ketoglutarate have a catalytic effect on the consumption of oxygen in a cell suspension.The rate of oxygen consumption is far more than that required for their own oxidation.This is evidence that ________.

Accepted Answer

The fact that succinate, fumarate, and α-ketoglutarate are causing a higher rate of oxygen consumption than needed for their own oxidation suggests that they are involved in a cyclic pathway. This type of cyclic pathway is known as the citric acid cycle (also called the Krebs cycle or TCA cycle), which involves a series of redox reactions that ultimately result in the generation of ATP.

Question 19

In eukaryotes the enzymes of the citric acid cycle are found in the ________.

Accepted Answer

The enzymes of the citric acid cycle (also known as the Krebs cycle or TCA cycle) are located in the mitochondria of eukaryotic cells. This is because the citric acid cycle requires oxygen as a reactant and the mitochondria are the site of oxidative phosphorylation, where most of the cell's ATP is generated.

Question 20

Why were muscle cells and extracts the best choice for Krebs,Johnson and Szent-Györgyi to elucidate the cyclic nature of the citric acid cycle?

Accepted Answer

Muscle cells have high energy demands and rely heavily on the citric acid cycle for energy production. Therefore, the intermediates of the cycle are used almost exclusively for energy metabolism in muscle cells, making them an ideal system to study the cyclic nature of the citric acid cycle.

Quiz 13: The Citric Acid Cycle

Which carbon atom(s) of pyruvate is(are) first converted to carbon dioxide by pyruvate dehydrogenase complex?

Pyruvate passes through the outer mitochondrial membrane by ________.

Which is not a component of the pyruvate dehydrogenase complex?

Pyruvate translocase is a(n) protein that transports .

What are the fewest number of turns of the citric acid cycle needed before carbon radioactive in both carbons of the acetyl group in acetyl Co A are incorporated into all 4 carbons in every molecule of oxaloacetate produced?

When energy-rich acetyl CoA is oxidized to carbon dioxide,eight electrons are released.Most often,electrons are released in such reactions because

Pyruvate dehydrogenase kinase catalyzes

The pyruvate dehydrogenase complex is larger than a ribosome.In bacteria these complexes are located in the cytosol while they are found in ________ of eukaryotes

The order of prosthetic groups as they act in the three proteins of the PDH(pyruvate dehydrogenase) complex is:

The enzyme pyruvate translocase is located ________.

Some bacteria and anaerobic eukaryotes not using PDH(pyruvate dehydrogenase) form acetyl CoA and CO₂ from pyruvate with ________.

The citric acid cycle oxidizes pyruvate,and some of the pathway intermediates are starting materials for many biosynthetic pathways.This means that the citric acid cycle is ________.

Most of the energy released in citric acid cycle reactions is conserved in ________.

The arrangement of subunits in the PDH(pyruvate dehydrogenase) complex ensures that ________.

Which cofactor is not used by the pyruvate dehydrogenase complex?

The net effect of the eight steps of the citric acid cycle is to

A deficiency in thiamine causes the disease beriberi.Which might you expect to have a higher than normal blood concentration in an individual with this condition?

Compounds like succinate,fumarate and α-ketoglutarate have a catalytic effect on the consumption of oxygen in a cell suspension.The rate of oxygen consumption is far more than that required for their own oxidation.This is evidence that ________.

In eukaryotes the enzymes of the citric acid cycle are found in the ________.

Why were muscle cells and extracts the best choice for Krebs,Johnson and Szent-Györgyi to elucidate the cyclic nature of the citric acid cycle?

Quiz 13: The Citric Acid Cycle

Which carbon atom(s) of pyruvate is(are) first converted to carbon dioxide by pyruvate dehydrogenase complex?

Pyruvate passes through the outer mitochondrial membrane by ________.

Which is not a component of the pyruvate dehydrogenase complex?

Pyruvate translocase is a(n) ________ protein that transports ________.

What are the fewest number of turns of the citric acid cycle needed before carbon radioactive in both carbons of the acetyl group in acetyl Co A are incorporated into all 4 carbons in every molecule of oxaloacetate produced?

When energy-rich acetyl CoA is oxidized to carbon dioxide,eight electrons are released.Most often,electrons are released in such reactions because

Pyruvate dehydrogenase kinase catalyzes

The pyruvate dehydrogenase complex is larger than a ribosome.In bacteria these complexes are located in the cytosol while they are found in ________ of eukaryotes

The order of prosthetic groups as they act in the three proteins of the PDH(pyruvate dehydrogenase) complex is:

The enzyme pyruvate translocase is located ________.

Some bacteria and anaerobic eukaryotes not using PDH(pyruvate dehydrogenase) form acetyl CoA and CO2 from pyruvate with ________.

The citric acid cycle oxidizes pyruvate,and some of the pathway intermediates are starting materials for many biosynthetic pathways.This means that the citric acid cycle is ________.

Most of the energy released in citric acid cycle reactions is conserved in ________.

The arrangement of subunits in the PDH(pyruvate dehydrogenase) complex ensures that ________.

Which cofactor is not used by the pyruvate dehydrogenase complex?

The net effect of the eight steps of the citric acid cycle is to

A deficiency in thiamine causes the disease beriberi.Which might you expect to have a higher than normal blood concentration in an individual with this condition?

Compounds like succinate,fumarate and α-ketoglutarate have a catalytic effect on the consumption of oxygen in a cell suspension.The rate of oxygen consumption is far more than that required for their own oxidation.This is evidence that ________.

In eukaryotes the enzymes of the citric acid cycle are found in the ________.

Why were muscle cells and extracts the best choice for Krebs,Johnson and Szent-Györgyi to elucidate the cyclic nature of the citric acid cycle?

Pyruvate translocase is a(n) protein that transports .

Some bacteria and anaerobic eukaryotes not using PDH(pyruvate dehydrogenase) form acetyl CoA and CO₂ from pyruvate with ________.