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Harvesting Energy:

Harvesting Energy:

Glycolysis and Cellular

Glycolysis and Cellular

Respiration

Respiration

Chapter 8 Chapter 8

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Overview of Glucose

Overview of Glucose

Breakdown

Breakdown

 The overall equation for the complete The overall equation for the complete breakdown of glucose is:

breakdown of glucose is:

CC66HH1212OO66 + 6O + 6O22  6CO 6CO22 + 6H + 6H22O + ATPO + ATP

 The main stages of glucose metabolism are:The main stages of glucose metabolism are:

GlycolysisGlycolysis

Cellular respiratioCellular respirationn

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Overview of Glucose

Overview of Glucose

Breakdown

Breakdown

GlycolysisGlycolysis

Occurs in the cytosol Occurs in the cytosol

Does not require oxygenDoes not require oxygen

Breaks glucose into pyruvateBreaks glucose into pyruvate

Yields two molecules of ATP per molecule of Yields two molecules of ATP per molecule of glucos

glucosee

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Overview of Glucose

Overview of Glucose

Breakdown

Breakdown

 If oxygen is absent fermentation occursIf oxygen is absent fermentation occurs

pyruvate is converted into either lactate, or into pyruvate is converted into either lactate, or into ethanol and CO

ethanol and CO22

 If oxygen is present cellular respiration If oxygen is present cellular respiration occur

occurss

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Overview of Glucose

Overview of Glucose

Breakdown

Breakdown

 Cellular respiration Cellular respiration

Occurs in Occurs in mitochondriamitochondria (in eukaryotes) (in eukaryotes) Requires oxygenRequires oxygen

Breaks down pyruvate into carbon dioxide and Breaks down pyruvate into carbon dioxide and water

water

Produces an additional 32 or 34 ATP Produces an additional 32 or 34 ATP molecules, depending on the cell typ molecules, depending on the cell typee

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Glycolysis

Glycolysis

• Glucose activation phaseGlucose activation phase

Glucose molecule converted to highly reactive Glucose molecule converted to highly reactive fructose bisphosphate by two enzyme-

fructose bisphosphate by two enzyme- catalyzed reactions, using 2 ATP

catalyzed reactions, using 2 ATPss

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Glycolysis

Glycolysis

• Energy harvesting phaseEnergy harvesting phase

Fructose bisphosphate is split into two three-Fructose bisphosphate is split into two three- carbon molecules of glyceraldehyde 3-

carbon molecules of glyceraldehyde 3- phosphate (G3P)

phosphate (G3P)

In a series of reactions, each G3P molecule is In a series of reactions, each G3P molecule is converted into a pyruvate, generating two

converted into a pyruvate, generating two

ATPs per conversion, for a total of four ATPs ATPs per conversion, for a total of four ATPs Because two ATPs were used to activate the Because two ATPs were used to activate the

glucose molecule there is a net gain of two glucose molecule there is a net gain of two ATPs per glucose molecul

ATPs per glucose moleculee

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Glycolysis

Glycolysis

1.1. Energy harvesting phase (continued)Energy harvesting phase (continued)

As each G3P is converted to pyruvate, two As each G3P is converted to pyruvate, two

high-energy electrons and a hydrogen ion are high-energy electrons and a hydrogen ion are added to an “empty” electron-carrier NAD+ to added to an “empty” electron-carrier NAD+ to make the high-energy electron-carrier

make the high-energy electron-carrier molecule NADH

molecule NADH

Because two G3P molecules are produced per Because two G3P molecules are produced per glucose molecule, two NADH carrier

glucose molecule, two NADH carrier molecules are formed

molecules are formed

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Glycolysis

Glycolysis

 Summary of glycolysis:Summary of glycolysis:

Each molecule of glucose is broken down to Each molecule of glucose is broken down to two molecules of pyruvate

two molecules of pyruvate

A net of two ATP molecules and two NADH A net of two ATP molecules and two NADH (high-energy electron carriers) are forme

(high-energy electron carriers) are formedd

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Fermentation

Fermentation

 Pyruvate is processed differently under Pyruvate is processed differently under aerobic and anaerobic conditions

aerobic and anaerobic conditions

 Under aerobic conditions, the high energy Under aerobic conditions, the high energy electrons in NADH produced in glycolysis electrons in NADH produced in glycolysis are ferried to ATP-generating reactions in are ferried to ATP-generating reactions in the mitochondria, making NAD+ available the mitochondria, making NAD+ available

to recycle in glycolysi to recycle in glycolysiss

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Fermentation

Fermentation

 Under anaerobic conditions, pyruvate is Under anaerobic conditions, pyruvate is converted into lactate or ethanol, a

converted into lactate or ethanol, a process called fermentation

process called fermentation

 Fermentation does not produce more Fermentation does not produce more

ATP, but is necessary to regenerate the ATP, but is necessary to regenerate the

high-energy electron carrier molecule high-energy electron carrier molecule

NAD+, which must be available for NAD+, which must be available for

glycolysis to continu glycolysis to continuee

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Fermentation

Fermentation

 Some cells ferment pyruvate to form acidsSome cells ferment pyruvate to form acids

 Human muscle cells can perform Human muscle cells can perform fermentation

fermentation

Anaerobic conditions produced when muscles Anaerobic conditions produced when muscles use up O

use up O22 faster than it can be delivered (e.g. faster than it can be delivered (e.g.

while sprinting) while sprinting)

Lactate (lactic acid) produced from pyruvatLactate (lactic acid) produced from pyruvatee

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Fermentation

Fermentation

 Some microbes ferment pyruvate to other Some microbes ferment pyruvate to other acids (as seen in making of cheese, yogurt, acids (as seen in making of cheese, yogurt,

sour cream) sour cream)

 Some microbes perform fermentation Some microbes perform fermentation

exclusively (instead of aerobic respiration) exclusively (instead of aerobic respiration)

 Yeast cells perform Yeast cells perform alcoholic fermentatioalcoholic fermentationn

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Cellular Respiration

Cellular Respiration

In eukaryotic cells, cellular respiration occurs In eukaryotic cells, cellular respiration occurs within

within mitochondriamitochondria, organelles with two , organelles with two membranes that produce two compartments membranes that produce two compartments The inner membrane encloses a central The inner membrane encloses a central

compartment containing the fluid

compartment containing the fluid matrixmatrix The outer membrane surrounds the The outer membrane surrounds the

organelle, producing an

organelle, producing an intermembrane intermembrane spacspacee

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Pyruvate Breakdown in

Pyruvate Breakdown in

Mitochondria

Mitochondria

• After glycolysis, pyruvate diffuses into the After glycolysis, pyruvate diffuses into the mitochondrion into the matrix space

mitochondrion into the matrix space

• Pyruvate is split into COPyruvate is split into CO22 and a 2-carbon and a 2-carbon acetyl group, generating 1 NADH per

acetyl group, generating 1 NADH per pyruvat

pyruvatee

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Pyruvate Breakdown in

Pyruvate Breakdown in

Mitochondria

Mitochondria

• Acetyl group is carried by a helper Acetyl group is carried by a helper

molecule called Coenzyme A, now called molecule called Coenzyme A, now called

Acetyl CoA Acetyl CoA

• Acetyl CoA enters the Krebs Cycle and is Acetyl CoA enters the Krebs Cycle and is broken down into

broken down into COCO22

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Pyruvate Breakdown in

Pyruvate Breakdown in

Mitochondria

Mitochondria

• Electron carriers NADElectron carriers NAD++ and FAD are and FAD are loaded with electrons to produce 3 loaded with electrons to produce 3

NADH & 1 FADH

NADH & 1 FADH22 per Acetyl CoA per Acetyl CoA

6. One ATP also made per Acetyl CoA in 6. One ATP also made per Acetyl CoA in

the Krebs Cycl the Krebs Cyclee

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Electron Transport Chain

Electron Transport Chain

 Most of the energy in glucose is stored in Most of the energy in glucose is stored in electron carriers NADH and FADH

electron carriers NADH and FADH22

Only 4 total ATP produced per glucose after Only 4 total ATP produced per glucose after complete breakdown in the Krebs Cycle

complete breakdown in the Krebs Cycle

 NADH and FADHNADH and FADH22 deposit electrons into deposit electrons into electron transport chains

electron transport chains in the inner in the inner mitochondrial membrane

mitochondrial membrane

 Electrons join with oxygen gas and Electrons join with oxygen gas and hydrogen ions to made H

hydrogen ions to made H22O at the end of O at the end of the ETC

the ETCss

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Chemiosmosis

Chemiosmosis

1.1. Energy is released from electrons as they Energy is released from electrons as they are passed down the electron transport

are passed down the electron transport chain

chain

2.2. Released energy used to pump hydrogen Released energy used to pump hydrogen ions across the inner membrane

ions across the inner membrane

Hydrogen ions accumulate in intermembrane Hydrogen ions accumulate in intermembrane spacspacee

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Chemiosmosis

Chemiosmosis

1.1. Hydrogen ions form a concentration Hydrogen ions form a concentration

gradient across the membrane, a form of gradient across the membrane, a form of

stored energy stored energy

• Hydrogen ions flow back into the matrix Hydrogen ions flow back into the matrix through an ATP synthesizing enzyme

through an ATP synthesizing enzyme

Process is called Process is called chemiosmosichemiosmosiss

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Chemiosmosis

Chemiosmosis

• Flow of hydrogen ions provides energy to Flow of hydrogen ions provides energy to link 32-34 molecules of ADP with

link 32-34 molecules of ADP with phosphate, forming 32-34 ATP

phosphate, forming 32-34 ATP

• ATP then diffuses out of mitochondrion ATP then diffuses out of mitochondrion

and used for energy-requiring activities in and used for energy-requiring activities in

the cel the celll

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Influence on How Organisms

Influence on How Organisms

Function

Function

 Metabolic processes in cells are heavily Metabolic processes in cells are heavily

dependent on ATP generation (cyanide kills dependent on ATP generation (cyanide kills

by preventing this) by preventing this)

 Muscle cells switch between fermentation Muscle cells switch between fermentation and aerobic cell respiration depending on O and aerobic cell respiration depending on O22

availabilit availabilityy

References

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