BIOC 2300 Lecture Notes - Lecture 19: Pyruvate Dehydrogenase, Acetyl-Coa, Citric Acid Cycle

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rubycheetah358

3 May 2018

School

Dalhousie University

Department

Biochem & Molecular Biology

Course

BIOC 2300

Professor

Dr.Barbara Karten

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Citric Acid Cycle

March 2, 2016

Pyruvate: anaerobic fermentation, aerobic oxidation, anaplerotic carboxylation

• Aerobic – mitrocondrial conversion of pyruvate to acetyl-CoA and oxidation in TCA

• Anaerobic: cytosolic regeneration of NAD+

The citric acid cycle is the final part of the oxidation of nutrients to CO2

• All nutrients broken down to acetyl-CoA

• Cycle oxidizes acetyl-CoA to CO2 and reduces NAD+ and FAD to NADH and FADH2

• …….

The oxidation of pyruvate to acetyl-CoA and the TCA cycle reactions take place in the mitochondria

• compartmentation

o allows additional regulation of metabolic pathways

o brings metabolites of one pathway to closer vicinity  faster reaction, less risk of

unwanted side reaction

• no mitochondria – no citric acid cycle

• all metabolites for cycle must be imported into mitochondria

Oxidation of pyruvate to acetyl-CoA

• catalyzed by pyruvate dehydrogenase

• pyruvate + NAD+ + CoASH  Acetyl-CoA + NADH + CO2 + H+

• requires:

o NAD+ (vitamin B3)

o TPP (B1)

o FAD (B2)

o CoA-SH

o Lipoic acid

• The oxidation of pyrivate to acetyl-CoA is irreversible

• Acetyl-CoA cannot be converted to glucose

• Pyruvate  glucose via gluconeogenesis

Coenzyme A

• Derivative of ADP, panthenic acid linked it via a phosphate ester bond

• Attached to pantothenic acid is a mercaptoethylamine group

• The thiol group can form thioester bonds which are more reactive than carboxylesters 

coexyme A can transfer acyl groups

• CoASH = CoA with a –SH group

• Activated form of acetate

• Can enter several pathways:

o Oxidation in TCA

o Precursor for larger metabolites

Enzyme activity can be regulated by phosphorylation: regulation of Pyruvate dehydrogenase (PDH)

• {DH is allosterically inhibited by acetyl-CoA and NADH (product inhibition)

• PDH kinase phosphorylates PDH and inactivates PSH

• PDH phosphatase dephosphorylates PDH and activates PDH

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Document Summary

Pyruvate: anaerobic fermentation, aerobic oxidation, anaplerotic carboxylation: aerobic mitrocondrial conversion of pyruvate to acetyl-coa and oxidation in tca, anaerobic: cytosolic regeneration of nad+ The citric acid cycle is the final part of the oxidation of nutrients to co2: all nutrients broken down to acetyl-coa, cycle oxidizes acetyl-coa to co2 and reduces nad+ and fad to nadh and fadh2. Enzyme activity can be regulated by phosphorylation: regulation of pyruvate dehydrogenase (pdh: {dh is allosterically inhibited by acetyl-coa and nadh (product inhibition, pdh kinase phosphorylates pdh and inactivates psh, pdh phosphatase dephosphorylates pdh and activates pdh. The citric acid cycle: mitochondrial generation of reducing units for oxidative phosphorylation, condensation of acetyl coa and oxaloacetate, reduction od nad+ and fad. Steps to citrate cycle: citrate synthase: condensation of oxaloacetate with acetyl-coa to citrate. Irreversible: aconitase: isomerization of isocitrate by dehydration-hydration. Kgdh is sensitive to thiamine deficiencies: succinyl-coa synthetase. Thioester is higher energy bond (hydrolysis makes gtp) Gtp easily converted to atp: succinate dehydrogenase.

Related Questions

2. In many cases, cellular signal transduction is mediated by a membrane-associated G-protein complex. Which is not right about this protein complex?

A) The complex is made of Î±-, Î²-, and Î³-subunit.

B) The G_sÎ±-subunit has a GTPase activity.

C) Depending on the receptor types, either G_sÎ±-subunit or G_iÎ±-subunit is used.

D) Signal transduction through G-proteins ultimately regulates protein phosphorylation.

E) None of the above.

3. Which statement is not right about the pyruvate dehydrogenase?

A) This enzyme is located in the mitochondria.

B) This enzyme consists of three different enzymatic subunits (E1, E2, and E3).

C) This enzyme catalyzes the reaction: Pyruvate + CoA + NAD Â® Acetyl-CoA + CO₂ + NADH

D) This enzyme also uses TPP (thiamine pyrophosphate), lipoic acid, and FAD as cofactors.

E) Despite its complexity, this enzyme is not an important regulation point of TCA cycle.

4. To maintain a proper rate of the TCA cycle, oxaloacetate is replenished periodically. To increase [oxaloacetate], ___X____ is turned on but the TCA cycled is turned off by phosphorylation of __Y__.

A) X = Glyoxylate cycle :::::: Y = isocitrate dehydrogenase

B) X = Glyoxylate cycle :::::: Y = isocitrate lyase

C) X = Q cycle :::::: Y = isocitrate dehydrogenase

D) X = Q cycle :::::: Y = isocitrate lyase

E) None of the above.

5. Assume you have three NADH and one FADH₂. Calculate the total numbers of H⁺ pumped into the inter-membrane space and the maximal number of ATP produced inside the matrix.

A) 40 H⁺ and 12 ATP
B) 40 H⁺ and 11 ATP
C) 36 H⁺ and 12 ATP

D) 36 H⁺ and 11 ATP
E) None of the above.

Why does an electron have lower potential energy in an H-O bondthan in an O=O bond?

H has a higher electronegativity than O.

O=O is not stable.

O=O contains a double bond.

The electrons are closer to the oxygen atom in the H-O bond.

None of the answers are correct.

How is the energy from the electron transport chain used mostdirectly?

to form the bonds of a water molecule

to pump hydrogen ions across the mitochondrial inner membraneinto the mitochondrial intermembrane space

to join ADP with a phosphate

to decompose glucose into pyruvate

to rotate ATP synthase

Which process provides the energy needed to pump protons acrossthe mitochondrial membrane during oxidative phosphorylation?

the transfer of electrons in redox reactions

the breakdown of ATP to ADP

the rotation of the ATP synthase rotor

oxidation of isocitrate

None of the answers are correct.

What causes the ATP synthase rotor to spin?

the passing of electrons through ATP synthase

the movement of protons across the mitochondrial membrane

the movement of electrons across the mitochondrial membrane

the synthesis of ATP from ADP and a phosphate group

None of the answers are correct.

What of the following generates the proton-motive force duringoxidative phosphorylation?

buildup of NADH molecules at protein complex I

movement of H⁺ ions across the mitochondrial membraneduring electron transport

rotation of the ATP synthase rotor

joining of H⁺ ions with oxygen to form water

None of the answers are correct.

Suppose a microorganism invades a cell, causing damage to ATPsynthase. How would cellular respiration be affected?

Electrons could not be passed down the electron transportchain.

ADP could not be joined with a phosphate to form ATP.

Hydrogen ions could not be pumped into the mitochondrialintermembrane space.

The cell could not release any energy from the glucosemolecule.

Glucose could not be broken down into pyruvate.

Which molecules transport electrons from the citric acid cycleto the electron transport chain?

NADH and FADH₂

ATP and ADP

GTP and GDP

oxaloacetate and citric acid

None of the answers are correct.

Which type of reactions control the energy release from glucoseduring the citric acid cycle?

acid-base reactions

redox reactions

random reactions

All answers are correct.

None of the answers are correct.

What is the role of NAD⁺ in cellular respiration?

to receive electrons from the citric acid cycle and deliver themto the electron transport chain

to catalyze the synthesis of ATP from ADP

to accumulate in the mitochondrial intermembrane space tofacilitate ATP synthesis

to serve as a substrate to bind to acetyl-CoA at the beginningof the citric acid cycle

None of the answers are correct.

10.

Which molecule enters the citric acid cycle?

glucose

pyruvate

ATP

acetyl-CoA

None of the answers are correct.

apricotgoose897

_____What is added to a molecule such as ADP when it is phosphorylated?

_____ An anaerobic process in which pyruvate is converted to lactate

_____ A biochemical process that breaks down food molecules to produce other molecules for cellular maintenance.

_____What is the final end product of Glycolysis?

_____ Refers to the potential energy provided by a large hydrogen-cation concentration gradient, and itâs movement across a biological membrane during chemiosmosis.

_____ A molecule that transfers or shuttles electrons during redox reactions.

_____ An organism that can survive in the presence or absence of oxygen.

_____ A type of enzyme that teams with NAD⁺ to remove hydrogen atoms with their electrons.

_____ The loss of electrons from one molecule to another.

_____ A process in which ATP is produced using the energy stored in concentration gradients.

_____ The products produced during a biochemical reaction that fall between the starting molecule and the end product.

_____ Biochemical process in which a glucose molecule is degraded to two pyruvates.

_____ Short for âreduction/oxidationâ reactions

_____How many pyruvate molecules are produced from a single Glyceraldehyde 3-phosphate?

_____ The formation of ATP occurring when an enzyme transfers a phosphate group from an organic molecule to ADP.

_____ Organisms that will die in the presence of oxygen.

_____ A term referring to the presence of oxygen.

_____ A series of electron-carrier molecules that shuttle electrons during the redox reactions that release energy used to make ATP.

_____ A biochemical process in which pyruvate is produced without the presence of oxygen.

20._____ The metabolic cycle that is fueled by Acetyl CoEnzyme A; occurs in the matrix of the mitochondria and supplies most of the NADH molecules that carry energy to the electron transport chain.

_____What is the chemical formula for Cellular Respiration?

_____What environmental condition is necessary for Anaerobic Respiration to occur?

_____Where does the Electron Transport Chain occur in the mitochondria?

_____Where does Glycolysis occur in a cell?

_____ An anaerobic process in which CO₂ is released as a byproduct and ethanol is produced as a product.

_____Where does the Krebs cycle occur in the mitochondria?

_____ The gain of electrons from one molecule to another.

_____ A high-energy fuel molecule that begins the Citric Acid Cycle.

_____What condition is necessary of Aerobic Respiration to occur?

_____ A term referring to the absence of oxygen.

_____What compound is derived from B vitamins, and helps the Acetyl portion of Acetyl CoA into the Krebs Cycle?

_____What is the name of the molecule that channels protons, providing the energy necessary to phosphorylate ADP to ATP?

_____In the blank, write the number of ATP^âs that can be synthesized from 3 NADH molecules.

_____In the blank, write the number of ATP^âs that can be synthesized from a single FADH₂ molecule.

_____What is the final electron acceptor in cellular respiration?

_____What molecule is regenerated during the process of the Krebs Cycle?

_____What enzyme is used to catalyzed the reaction that occurs during the formation of Acetyl CoA?

_____How many pyruvates are produced from a single glucose molecule?

_____How many Acetyl CoA molecules are produced from a single glucose molecule?

_____What is the reduced form of Nicotinamide Adenine Dinucleotide?

_____What is the oxidized form of Flavin Adenine Dinucleotide?

42._____ A membrane protein that is used in conjunction with chemiosmosis to produced ATP.

I know that this alot of questions, but it's kinda a last ditch effort. these are the last 42 definitions i have left to answer out of 500 question for my final exam study guide. so whatever help i can get is fine. No explanations needed just what each definition is explaining and thanks in advance ladies and gentlemen.

scarletlocust623

BIOC 2300 Lecture Notes - Lecture 19: Pyruvate Dehydrogenase, Acetyl-Coa, Citric Acid Cycle

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