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Wednesday, July 6, 2011

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What is the fate of Pyruvate?


GLYCOLYSIS

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PYRUVATE OX.

KREBS CYCLE

ETC

Stages of Cellular Respiration


The Krebs Cycle – does your head suddenly hurt?

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The Krebs Cycle – An Overview

• In the presence of O2, the pyruvate of most cells enters the Krebs cycle (citric acid cycle), in which each pyruvate is oxidized to three molecules of CO2.

• 6 additional NAD+ molecules are reduced to 6 NADH, and 2 FAD+ (a second electron carrier) are reduced to form 2 FADH2.

• 2 additional ATPs are formed as the 2 pyruvates are oxidized in the Krebs cycle.

• The Krebs cycle occurs in the mitochondria of eukaryotic Wednesday, July 6, 2011

http://upload.wikimedia.org/wikipedia/commons/e/ea/Diagram_of_an_animal_mitochondrion.svg
















































MitochondriaFunction• Mitochondria are cell

organelles.• They are often called the

powerhouses of the cell because they contain enzymes that help metabolize food into ATP.

• The ATP is generated through several oxidation reactions.

• All cells have different numbers of mitochondria. Cells that require a lot of energy usually have more.

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Structure• Mitochondria have two membranes: 1)outer membrane2)inner membrane that is folded into structures called cristae.

•The inner fluid of the mitochondria is called the matrix.•There are hundreds of enzymes in the matrix.


Anatomy of the Mitochondria

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A

B

C

D


• Pyruvate is oxidized in the mitochondria to produce acetyl-CoA and CO2

• This reaction is a link between glycolysis and the reactions of the Krebs cycle as acetyl-CoA is used by the Krebs cycle.

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The Krebs Cycle – Oxidation of Pyruvate (transition step)


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A 3 carbon molecule of pyruvate

enters the mitochondrion from the cytoplasm. One atom is removed via and hydrogen is removed using

carbondecarboxylation

NAD+.

Coenzyme A (CoA) becomes attached to the remaining

2 carbon atoms, creating Acetyl-CoA, which enters the

Krebs cycle.



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What is the word reaction for pyruvate oxidation?

Pyruvate + NAD+ + CoA acetyl-CoA + NADH + CO2 + H+


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The Krebs Cycle

most enzymes for these rxns are located in mitochondrial matrix

8 steps w/ 8 dif. enzymes

oxaloacetate is recycled

cycle turns twice for every glucose molecule oxidized


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The Krebs Cycle

Acetyl-CoA enters the cycle and then combines with

oxaloacetate to make the 6-carbon compound citrate.

During the eight steps of the Krebs cycle, citrate undergoes

a number of reactions, releasing CO2 and ATP

in a number of steps. Citrate is eventually converted into

oxaloacetate so it can be used again during the Krebs cycle.


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The Krebs Cycle – The Products

1. is released as waste.

NADH and

respiration.

3. Energy is released in the form of ATP.

A glucose molecule produces two

because two molecules of

CO2

2. FADH2 move to the next stage of cellular

molecules of ATP.

pyruvate are created from

each molecule of glucose


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The Krebs Cycle

Used the diagram in the next panel to determine the products of the Krebs Cycle, both per each acetyl and glucose molecule: per acetyl molecule per glucose molecule ___NADH ___ NADH ____FADH2 ____ FADH2 ___ATP (subs. level) ____ ATP ___ CO2 ____ CO2


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How many oxidation reactions occur in Krebs? Where?

Where does the condensation reaction occur?

Where does the isomerization reaction occur?

Where does substrate-level phosphorylation occur?


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NADH and FADH2 transfer their electrons to the electron transport chain (ETC)

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LAST STEP!!! Electron Transport and Chemiosmosis


The electron transport chain (ETC) Series of proteins arranged along the

inner membrane (the cristae) Increasing negativity Get a series of redox reactions

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Free energy released with each redox

Oxygen is the final electron acceptor


ETC – the finer details NADH passes 2 electrons to NADH dehydrogenase Electrons are moved along the ETC

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ETC – the finer details Free E that is released is used to pump H+ from the

matrix intermembrane space For every pair of e-s, each protein pumps out one H+

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ETC – the finer details When oxygen is reduced, it also binds 2 H+,

and forms one H2O (inside the matrix)

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Chemiosmosis = ATP formation

Proton-motive force drives H+ through an ATPase complex. Free energy released.◦ Drives phosphorylation of ADP ATP

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Electrochemical (E.C.) gradient established across membrane by H+◦ High [H+] in intermembrane space


Energy accountingOne ATP formed for every H+ that moves in

through ATPase

For each pair of e-’s, one H+ is pumped in by each of the three stationary proteins in the ECT.

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3 ATP for every NADH

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2 ATP for every FADH2◦ FADH2 passes its e-’s to cytochrome b-c1 complex


Conversion (cashing out)3 ATP per NADH: 3 ATP x 8 NADH = 24 ATP

2 ATP per FADH2

2 ATP x 4 FADH2 = 8 ATP

= 32 ATP (ETC) + 4 ATP (glycol./Krebs)

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Summary of processC6H12O6 + 6O2 6CO2 + 6H2O +

energy

Glucose is oxidized to carbon dioxide.

Oxygen is reduced to water.

36 molecules of ATP are produced.

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