Ch. 6 Glycolysis-krebs-ETC (1)

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

•  Cellular respiration oxidizes sugar and produces ATP in three main stages

– Glycolysis occurs in the cytoplasm

– The Krebs cycle and the electron transport chain occur in the mitochondria

6.8 Overview: Respiration occurs in three main stages

STAGES OF CELLULAR RESPIRATION AND FERMENTATION


Mitochondrion

CO2 CO2

NADH

ATP

High-energy electrons carried by NADH

NADH

CITRIC ACID CYCLE

GLYCOLYSIS Pyruvate Glucose

and FADH2

Substrate-level phosphorylation

Substrate-level phosphorylation

OXIDATIVE PHOSPHORYLATION

(Electron Transport and Chemiosmosis)

Oxidative phosphorylation

ATP ATP

Cytoplasm Inner mitochondrial membrane


Remember NADP+/NADPH from Photosynthesis???

•  It was a high energy electron carrier!

•  In respiration we have NAD+ that carries high energy electrons and a hydrogen ion in the form of NADH

•  FAD is also an electron and hydrogen ion carrier and becomes FADH2

•  These will become important in the ETC


REDOX reactions

•  LEO goes GER

•  Lose electron- oxidation

•  Gain electron- reduction


6.6 Overview: Cellular respiration occurs in three main stages

•  Stage 1: Glycolysis

– Glycolysis begins respiration by breaking glucose, a six-carbon molecule, into two molecules of a three-carbon compound called pyruvate

– This stage occurs in the cytoplasm

Copyright © 2009 Pearson Education, Inc.


6.9 Glycolysis harvests chemical energy by oxidizing glucose to pyruvic acid

Figure 6.9A

Glucose Pyruvic acid

* Pyruvic acid = Pyruvate


Summary of Glycolysis

•  In

Glucose (6-C)

2 ADP

2 NAD+

•  Out

2 pyruvate; 2(3-C)

2 ATP (net)

2 NADH


Questions

•  Where does glycolysis take place?

•  Glycolysis energy yield?

•  Breaks glucose into TWO ________.

•  Animation



•  Stage 2: The citric acid (Krebs) cycle

– The Krebs cycle breaks down pyruvate into carbon dioxide and supplies the third stage with electrons

– This stage occurs in the mitochondria



•  Each pyruvic acid molecule is broken down to form CO2 and a two-carbon acetyl group, which enters the Krebs cycle

6.10 Pyruvic acid is chemically groomed for the Krebs cycle

Figure 6.10

Pyruvic acid

CO2

Acetyl CoA (acetyl coenzyme A)


•  The Krebs cycle is a series of reactions in which enzymes strip away electrons and H+ from each acetyl group

6.11 The Krebs cycle completes the oxidation of organic fuel, generating many NADH and FADH2 molecules

Figure 6.11A

Acetyl CoA

KREBS CYCLE

2 CO2


Citric Acid Production

The Krebs Cycle Section 9-2

Mitochondrion


Citric Acid Production

Figure 9–6 The Krebs Cycle Section 9-2

Mitochondrion


Summary

•  In

Pyruvate -> Acetyl CoA

NAD+

FAD

ADP

•  Out

CO2 (as waste)

NADH

FADH2

(LOTS OF ELECTRONS!!)

2 ATP


Questions

•  Where does the Krebs cycle take place?

•  How many ATP are produced?

Animation



•  Stage 3: Oxidative phosphorylation/Electron Transport Chain

– During this stage, electrons are shuttled through the electron transport chain

– As a result, ATP is generated through oxidative phosphorylation associated with chemiosmosis

– This stage occurs in the inner mitochondrion membrane



•  The electrons from NADH and FADH2 travel down the electron transport chain to oxygen

•  Energy released by the electrons is used to pump H+ into the space between the mitochondrial membranes

•  In chemiosmosis, the H+ ions diffuse back through the inner membrane through ATP synthase complexes, which capture the energy to make ATP (same as photosynthesis!)

Chemiosmosis powers most ATP production


ATP

H+

Intermembrane space

O2

H2O

1 - 2

Inner mitochondrial membrane

H+ NAD+

H+

H+

H+ H+

H+ H+

H+

H+

H+

H+

H+

H+

Mitochondrial matrix

Electron flow

Electron carrier

Protein complex of electron carriers

NADH

FADH2 FAD

ATP synthase

P ADP +

Chemiosmosis

+ 2

OXIDATIVE PHOSPHORYLATION

Electron Transport Chain


Summary

In

Oxygen

NADH (carrying electrons)

FADH2 (carrying electrons)

Out

H20

NAD+

FAD

LOTS OF ATP!!!!!


What’s the take away message???

•  Glycolysis breaks down glucose into pyruvate

•  Pyruvate is made into acetyl- CoA (releasing CO2)

•  Krebs uses up acetyl- CoA and produces 2 ATP, more CO2, and LOTS OF ELECTRONS CARRIED BY NADH AND FADH2!


•  For each glucose molecule that enters cellular respiration, chemiosmosis produces up to 38 ATP molecules

6.14 Review: Each molecule of glucose yields many molecules of ATP

KREBS CYCLE

Electron shuttle across membranes

Cytoplasmic fluid

GLYCOLYSIS

Glucose 2

Pyruvic acid

2 Acetyl CoA

KREBS CYCLE

ELECTRON TRANSPORT CHAIN

AND CHEMIOSMOSIS

Mitochondrion

by substrate-level phosphorylation

used for shuttling electrons from NADH made in glycolysis

by substrate-level phosphorylation

by chemiosmotic phosphorylation

Maximum per glucose: Figure 6.14


The Mystery of the Toxic Flea Dip….


6.11 CONNECTION: Certain poisons interrupt critical events in cellular respiration

•  There are three different categories of cellular poisons that affect cellular respiration

– The first category blocks the electron transport chain (for example, rotenone, cyanide, and carbon monoxide)

– The second inhibits ATP synthase (for example, oligomycin)

– Finally, the third makes the membrane leaky to hydrogen ions (for example, dinitrophenol)



ATP

H+

O2

H2O

1 - 2 H+ NAD+ NADH

FADH2 FAD

P ADP +

Chemiosmosis

+ 2

Electron Transport Chain

H+ H+ H+

H+

Rotenone Cyanide, carbon monoxide

H+

H+

Oligomycin

ATP synthase

DNP

H+

H+

H+


Rotenone

•  Rotenone is a common pesticide

•  Rotenone interrupts the electron transport chain

•  It prevents NADH from transferring its electrons and therefore prevents the production of ATP

•  If NADH cannot transfer its electrons, there will be a substantial decrease of NAD+ molecules

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Ch. 6 Glycolysis-krebs-ETC (1)