Copyright © 2011 Pearson Education Inc.Biology: Life on Earth, 9e Chapter 8 Harvesting Energy: Glycolysis and Cellular Respiration

Copyright © 2011 Pearson Education Inc. Biology: Life on Earth, 9e

Chapter 8

Harvesting Energy: Glycolysis and Cellular Respiration


Photosynthesis Provides the Energy Released by Glycolysis and Cellular Respiration

ATP

H2O O2CO2C6H12O6

glycolysis

photosynthesis

energy from sunlight

cellularrespiration

66 6

Fig. 8-1

6 CO2 + 6 H2O + light energy C6H12O6 + 6 O2


How Do Cells Obtain Energy?

An overview of glucose breakdown– The overall equation for the complete breakdown of

glucose is

C6H12O6 + 6 O2 6 CO2 + 6 H2O + ATP + heat



An overview of Glycolysis– The first stage of glucose breakdown is glycolysis

– Splitting of glucose (a six-carbon sugar) into two molecules of pyruvate (a three-carbon sugar)

– Two ATP molecules are produced– Glycolysis proceeds in the same way under aerobic

(with oxygen) or anaerobic (without oxygen) conditions

– Glycolysis occurs in the cytoplasm



An overview of Cellular Respiration– The second stage of glucose breakdown is aerobic

respiration and occurs when oxygen is available– Two pyruvate molecules are broken down into six

carbon dioxide molecules and six water molecules– For every two pyruvate molecules, an additional 34 or

36 ATP molecules are generated– Cellular respiration occurs in mitochondria



An overview of Aerobic fermentation– If oxygen is not available, the second stage of glucose

breakdown is fermentation– Fermentation does not produce any ATP– Pyruvate remains in the cytoplasm and is converted

into lactate or ethanol + CO2


A Summary of Glucose Breakdown

Fig. 8-2

cellularrespiration

glucose

glycolysis

fermentation2 pyruvate

lactate

ethanol+

CO2

(cytoplasmicfluid)

mitochondrion

ATP

CO2

34or36

ATP2

6 H2O

O2

6

6

If no O2 is availableIf O2 is available


What Happens During Glycolysis?

Glucose activation – A glucose molecule is activated when it receives two

phosphates from two ATPs, becoming fructose bisphosphate– Two ATPs are converted into two low-energy

adenosine diphosphate (ADP) molecules


What Happens During Glycolysis?

Energy harvesting– The six-carbon fructose bisphosphate is split into two,

three-carbon molecules of glyceraldehyde-3-phosphate (G3P)

– In a series of reactions, each of the two G3P molecules is converted into a pyruvate, generating two ATPs per conversion, for a total of four ATPs

– As each G3P is converted to pyruvate, two high-energy electrons and a hydrogen ion are added to an “empty” electron-carrier nicotinamide adenine dinucleotide (NAD+) to make the high-energy electron-carrier molecule NADH


Fig. 8-3

glucosefructose

bisphosphate

G3P pyruvate

NAD+

ADPATP

2

2 2

22

4 4

2

ADP

NADH

ATP

Energy harvestGlucose activation

CC CCCC CC CC C CC C CCCC

PPP

1 2

The Essentials of Glycolysis

Summary of Glycolysis – Each molecule of glucose is broken down to two

molecules of pyruvate– A net of two ATP molecules and two NADH are produced

Copyright © 2011 Pearson Education Inc. Biology: Life on Earth, 9e outer membrane

inner membraneintermembrane space

matrix

What Happens During Cellular Respiration? Cellular respiration in eukaryotic cells occurs in

mitochondria in three stages1. Pyruvate is broken down in the mitochondrial matrix,

– Keep in mind that each glucose molecule produces two pyruvate molecules

2. High-energy electrons travel through the electron transport chain

3. ATP is generated by

chemiosmosis


What Happens During Cellular Respiration?

1. Mitochondria matrix reactions The formation of acetyl CoA

– Pyruvate is split, forming an acetyl group and releasing CO2

– The acetyl group reacts with Coenzyme A, forming acetyl CoA

– During this reaction, two high-energy electrons and a hydrogen ion are transferred to NAD+, forming NADH



1. Mitochondria Matrix reactions The Krebs cycle / Citric Acid cycle

– Acetyl CoA is combined with a four-carbon molecule to form six-carbon citrate, and coenzyme A is released

– Enzymes in the matrix break down the acetyl group, releasing two CO2 molecules and regenerating the four-carbon molecule for use in future cycles

– Each acetyl group produces one ATP, three NADH, and one FADH2


Reactions in the Mitochondrial Matrix

Fig. 8-5ATP

ADP

– CoAacetyl CoA

CO2

pyruvate

C

C

CCCCC CO22

coenzyme A

FADH2

NAD+

FAD

3

3 NAD+

NADH

NADH

coenzyme A

Formation ofacetyl CoA

Krebscycle

1

2



2. Membrane reactions Electron transport chain (ETC)

– 10 NADH and 2 FADH for one glucose molecule– These high-energy electrons jump from molecule to

molecule in the ETC, losing small amounts of energy at each step

– The energy-depleted electrons are transferred to oxygen, which acts as a final electron acceptor

– Energy-depleted electrons, oxygen, and hydrogen ions combine to form water


e–2 e–2e–2 2 H+

H+

H+

H+

H+

H+

H+

H+

H2OO212

FAD

ATP

FADH2

NAD+

NADH

P

ADP

(intermembrane space)

(innermembrane)

ETC

(matrix)

ATPsynthase

13

4

2

What Happens During Cellular Respiration?3. Chemiosmosis

– This energy is harnessed to pump H+ into the intermembrane space, producing a high concentration of H+

– The energy is then captured in the bonds of ATP as H+ flows down its gradient

– The flow of H+ through the synthase channel provides the energy to synthesize 32 or 34 molecules of ATP for each molecule of glucose


Summary of Cellular Respiration in Eukaryotic cells

Krebscycle

electron transport chain

glucose

glycolysis

2 acetyl CoA

CoA

2 pyruvate

(cytoplasmicfluid)

NADH

NADH

NADH

32or34

FADH2

ATP

ATP

ATP

total: 36 or 38 ATP

CO2

CO2

2

2

2

2

6

2

4

2

H2OO2

mitochondrion

Fig. 8-7

Lipids and proteins can also be used by converting them to pyruvate or acetyl CoA


What Happens During Fermentation?

Why is anaerobic fermentation necessary?– For glycolysis to continue, the NAD+ used to generate

NADH must constantly be regenerated– Under anaerobic conditions, with no oxygen to allow

the ETC to function, the cell must regenerate the NAD+ for glycolysis using fermentation in cytoplasm

– If the supply of NAD+ were to be exhausted, glycolysis would stop, energy production would cease, and the organism would rapidly die


What Happens During Fermentation?

Why is fermentation necessary? – Organisms use one of two types of fermentation to

regenerate NAD+

– Lactic acid fermentation produces lactic acid from pyruvate

– Alcohol fermentation generates alcohol and CO2 from pyruvate


What Happens During Fermentation? Some cells ferment pyruvate to form lactate

– Active muscle cells regenerate NAD+ by fermenting pyruvate to lactate, using electrons from NADH and hydrogen ions

– A variety of microorganisms that lack mitochondria, including the bacteria that convert milk into yogurt, sour cream, and cheese

NADH NADH NAD+NAD+

glucose

2

2 2 ATPADP

pyruvate lactate(fermentation)(glycolysis)

2CCCCCC CCC CCC

2 2 2 2

rnege eration

Fig. 8-8


What Happens During Fermentation? Some cells ferment pyruvate to form alcohol and

carbon dioxide– Many microorganisms, such as yeast– During alcohol fermentation, H+ and electrons from

NADH are used to convert pyruvate into ethanol and CO2; this releases NAD+, which can accept more high-energy electrons during glycolysis

NADH NADH NAD+NAD+

glucose

2

2 2 ATPADP

pyruvate ethanol CO2

(fermentation)(glycolysis)2 + 2CCCCCC CCC CCC

2 2 2 2

r nege eration

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Copyright © 2011 Pearson Education Inc.Biology: Life on Earth, 9e Chapter 8 Harvesting Energy: Glycolysis and Cellular Respiration