Chapter 10: Carbohydrate Metabolism II: Aerobic respiration

Question 1

What are the other names for the citric acid cycle?

Answer 1

Kreb cycle or the tricarboxylic acid (TCA) cycle.

Question 2

What is the main function of the citric acid cycle?

Answer 2

Oxidation of acetyl Co-A to CO2 and H2O. In addition, the cycle produces the high energy electron carrying molecules NADH and FADH 2.

Question 2

Methods of forming Acetyl Co-A

Answer 2

Pyruvate enters the mitochondrion via active transport and is oxidized and decarboxylated. These reactions are catalyzed by a multi enzyme complex called the pyruvate dehydrogenase complex, which is located in the mitochondrial matrix.

Question 3

What are the five enzymes in the pyruvate dehydrogenase complex?

Answer 3

Private dehydrogenase (PDH), dihydrolipoyl transacetylase, dihydrolipoyl dehydrogenase, pyruvate dehydrogenase kinase, and pyruvate dehydrogenase phosphate.

Question 4

Coenzyme A.

Answer 4

It is written as CoA-SH, when Acetyl Co-A forms is thus so by covalent attachment to the acetyl group to the -SH group resulting in the formation of a thioester.

Question 5

Thioester bonds.

Answer 5

They have high energy properties. A significant amount of energy will be released. This can be enough to drive other reactions forward, like the citric acid cycle.

Question 6

What does pyruvate dehydrogenase (PDH) do?

Answer 6

Pyruvate is oxidized, yielding CO2, while the remaining 2 carbon molecules bind covalently to thiamine pyrophosphate (TPP).

Question 7

dihydrolipoyl transacetylase

Answer 7

The two carbon molecules bonded to TPP. Phosphate is oxidized and transferred to lipoic acid, creating an acetyl group. This little group is now bonded to lipoic acid via thioester linkage. After this dihydrolipoyl transacetylase catalyzes the Co-A-SH interaction with the newly formed thioester link, causing transfer of an acetyl group to form acetyl Co-A.

Question 8

dihydrolipoyl dehydrogenase

Answer 8

As the lipoicc acid is reoxidized, FAD is reduced to FADH2. And NAD+ is reduced to NADH.

Question 9

What are the other pathways capable of forming a acetyl Co-A?

Answer 9

Fatty acid oxidation, which happens in the cytosol, a process called activation, causes a thioester bond to form between carboxyl groups of fatty acids and Co-A-SH. Amino acid catabolism, certain amino acids can be used to form acetyl Co-A. These amino acids must lose their amino group via transamination. Carbon skeletons can then form ketone bodies. When alcohol is consumed, you moderate around the enzyme alcohol dehydrogenase and acetyl aldehyde. Dehydrogenase converts it to acetyl Co A.

Question 10

Where does the citric acid cycle takes place?

Answer 10

Mitochondrial matrix.

Question 11

How does the citric acid cycle begins?

Answer 11

Coupling of molecule of acetyl Co A to a molecule of oxaloacetate.

Question 12

Step one of citric acid cycle.

Answer 12

Citrate Formation. First, acetyl Co A and oxaloacetate undergo a condensation reaction to form Citryil- CoA. Then the hydrolysis of Citryil- CoA yields citrate and CoA-SH.

Question 13

What enzyme catalyzes the citrate formation In the citric acid cycle?

Answer 13

Citrate Synthase.

Question 14

Step 2 of citric acid cycle.

Answer 14

Citrate isomerized to isocitrate. This happens by a switching of hydrogen and a hydroxyl group.

Question 15

What enzyme catalyzes the isomerization of isocitrate from citrate?

Answer 15

Aconitase

Question 15

Step three of citric acid cycle.

Answer 15

Alpha ketoglutarate and CO2 formation. Isocitrate is first oxidized to oxalosuccinate by isocitrate dehydrogenase. Then oxalosuccinate Is decarboxylated to produce alpha ketoglutarate and CO2. The first of the two carbons from the cycle is lost here, as well as the first NADH produced from intermediates.

Question 16

What is the rate limiting enzyme of the citric acid cycle?

Answer 16

Isocitrate dehydrogenase.

Question 17

Step four of citric acid cycle.

Answer 17

Succinyl-CoA and CO2 formation. These reactions are carried out by the alpha ketoglutarate dehydrogenase complex, which is similar in mechanism cofactors to PDH. in the formation of Succinyl-CoA, Alpha ketoglutarate and CoA come together and produce a molecule of carbon dioxide.

Question 18

What is a dehydrogenase?

Answer 18

Dehydrogenases are subtype of oxidoreductase. Dehydrogenases transfer a hydride ion (H-) to an electron acceptor, usually NAD+ or FAD. Therefore, whenever you see dehydrogenase in aerobic metabolism beyond the lookout for a high energy electron carrier being formed.

Question 19

synthase versus synthetase.

Answer 19

synthase doesn’t require energy input in order to form covalent bonds. synthetase certainly does.

Question 20

What is the enzyme that catalyzes the formation of succinate?

Answer 20

Succinyl COA synthetase

Question 20

Step five in citric acid cycle.

Answer 20

Succinate formation. Hydrolysis of the thioester bond on succinyl CoA yields succinate and CoA-SH. It also happens to do phosphorylation of GDP to GTP.

Question 21

Step 6 in citric acid cycle.

Answer 21

Fumarate formation. It doesn’t occur in the mitochondrial matrix. Instead it occurs in the inner membrane. Succinate undergoes oxidation to yield fumarate.

Question 21

Step seven in the citric acid cycle.

Answer 21

Malate formation. The enzyme fumarase catalyzes the hydrolysis of the alkene bond in fumarate, thereby giving rise to malate.

Question 22

What is the enzyme that catalyzes fumarate formation?

Answer 22

Succinate Dehydrogenase. This is considered a flavoprotein because it is covalently bonded to FAD, the electron acceptor in this reaction. This enzyme is an integral protein on the inner mitochondrial membrane.

Question 22

Step eight in the citric acid cycle.

Answer 22

Oxaloacetate formed anew. The enzyme malate dehydrogenase catalyzes the oxidation of malate to oxaloacetate. A third and final molecule of NAD+ is reduced to NADH.

Question 23

net results in ATP yield.

Answer 23

Pyruvate dehydrogenase complex yields one NADH.

Citric acid cycle yields 3 NADH and one FADH2 and one GTP.

Question 23

Conversions of ATP.

Answer 23

NADH can be converted to approximately 2.5 ATP, while each FADH2 molecule can yield about 1.5 ATP.

Question 24

ATP Production.

Answer 24

Four NADH gives 10 ATP.

One FADH2 gives 1.5 ATP

One GTP gives one ATP.

Total is 12.5 ATP per pyruvate = 25 ATP per glucose.

Glycolysis yields 2 ATP and two NADH, providing another seven molecules of ATP. Therefore, the net yield of ATP for one glucose molecule from glycolysis through oxidative phosphorylation is 30 to 32 ATP.

Question 25

Pyruvate dehydrogenase kinase.

Answer 25

The mechanism by which the PDH is phosphorylated. Therefore inhibiting acetyl-CoA production.

Question 26

Pyruvate dehydrogenase phosphate.

Answer 26

It responds to high levels of ADP. It activates the pyruvate dehydrogenase complex, By removing a phosphate from PDH.

Question 27

Control points of citric acid cycle.

Answer 27

Citrate Synthase: ATP and NADH function is allostatic inhibitors of citrate synthase.

Isocitrate dehydrogenase: Inhibited by energy products such as ATP and NADH. Conversely, ADP and NAD plus function as allosteric activators for the enzyme and enhance its affinity for substrate.

Alpha ketoglutarate dehydrogenase complex: NADH function is inhibitors of this enzyme complex. It is stimulated by ADP and calcium ions.

Question 28

Regulators.

Answer 28

Regulators.

Question 29

Easy way to explain electron transport chain?

Answer 29

The electron rich molecules NADH and FADH2 are formed as by products at earlier steps in respiration. They transferred their electrons to carrier proteins located along the inner mitochondrion Membrane. These electrons are given to oxygen in the form of hydride ions and water is formed. Protons are moved from the mitochondrial matrix into the Intermembrane space of the mitochondria, thereby creating a greater concentration gradient of hydrogen ions that can be used to drive ATP production.

Question 30

What is the proton motive force?

Answer 30

Electrochemical proton gradient generated by the complexes of the electron transport chain.

Question 31

Is the formation of ATP and electron transport chain endergonic or exergonic?

Answer 31

The formation of ATP is endergonic and electron transport is an exergonic pathway. In order for energy to be harvested via electron transport reactions, the proteins along the inner membrane must transfer the electrons donated by NADH and FADH2 in a specific order and direction.

Question 32

What makes oxygen a great final acceptor in the electron transport chain?

Answer 32

It has a high reduction potential.

Question 33

How many protons are translocated in each complex?

Answer 33

Complex 1: translocate 4 protons.

Complex 2: No protons are pumped.

Complex 3: translocate 4 protons.

Complex 4: translocate 2 protons.

Question 33

The proton motive force.

Answer 33

As H+ increases in the intermembrane space. Two things happen simultaneously: PH jobs in the intermembrane space and the voltage difference between the intermembrane space and matrix increases due to proton pumping. Together, this is referred to as an electron chemical gradient, gradient that has both chemical and electrostatic properties. Any electrochemical gradient stores energy and it will be the responsibility of ATP synthesis to harness this energy to form ATP from ADP and an inorganic phosphate.

Question 34

What are the four complexes in the electron transport chain?

Answer 34

Complex 1 = NADH-CoQ Oxidoreductase : The transfers of electron from NADH to coenzyme Q is catalyzing this first complex.

Complex 2 = Succinate-CoQ Oxidoreductase : Receives electron from succinate and transfer it to coenzyme Q.

Complex 3 = CoQH2- Cytochrome C oxidoreductase: Transfers of electron from coenzyme Q to cytochrome C.

Complex 4 = Cytochrome C oxidase: Transfers of electrons from cytochrome C to an oxygen, the final electron acceptor.

Question 35

Shuttle mechanism.

Answer 35

shuttle mechanism transfers the high energy electron of any NADH to a carrier that can cross the inner mitochondria membrane. This is because cytosolic NADH Formed through glycolysis cannot directly cross into the mitochondrial matrix. There are two shuttles known: Glycerol 3-phosphate shuttle and malate-aspartate shuttle.

Question 36

Chemiosmotic coupling.

Answer 36

Allows the chemical energy of the gradient to be harnessed as a means of phosphorylating ADP, thus forming ATP. In other words, the ETC generates a high concentration of protons in the intermembrane space. The protons then flow through the F0 ion channel of ATP synthase back into the matrix.

Question 37

ATP’s synthase

Answer 37

has the Fo part, It functions as an ion channel, so protons travel through F0 along their gradient back into the matrix. The other part is F1 portion, which utilizes the energy released from this electrochemical gradient to phosphorylate ADP to ATP.

Question 38

What about the energy change and the reaction Of oxidative phosphorylation?

Answer 38

When proton motive force is dissipated through the F0 portion of ATP synthase, the free energy change of the reaction is negative, a highly exergonic reaction. This makes sense because phosphorylating ADP to ATP is an endergonic process.

Question 38

Confirmational coupling.

Answer 38

ATP’s released by the synthase as a result of conformational changes caused by the gradient. In this mechanism, the F1 portion of ATP synthase is reminiscent of a turbine.

Question 39

Regulation of oxidative phosphorylation.

Answer 39

Always think of O2 when ADP as their key regulators of oxidative phosphorylation. If O2 is limited, the rate of oxidative phosphorylation decreases and the concentration of NADH and FADH2 increase. The accumulation of NADH in turn inhibits the citric acid cycle. The coordinated regulation of this pathway is known as respiratory control. An accumulation of ADP is accompanied by a decrease in ATP and the amount of energy available to the cell.

Question 39

What is the difference between ETC and oxidative phosphorylation?

Answer 39

The ETC is made-up of physical set of intermembrane proteins located on the inner mitochondrial matrix and they undergo oxidation reduction reaction. As they transfer electrons to oxygen, the final electron acceptor. As electrons are transferred, a proton motive force is generated in the intermembrane space. Oxidative phosphorylation is the process by which ATP is generated via harnessing of the proton gradient and neutralizes ATP synthetase to do so.