Chapter 8 Chapter 8

How Cells Release Chemical EnergyHow Cells Release Chemical Energy

Overview of Energy Releasing Overview of Energy Releasing PathwaysPathways

All organisms release chemical bond energy All organisms release chemical bond energy from glucose and other organic compounds from glucose and other organic compounds to drive ATP formation.to drive ATP formation.

The main energy releasing pathways all The main energy releasing pathways all start in the cytoplasm.start in the cytoplasm.

Only aerobic respiration, which uses O, Only aerobic respiration, which uses O, ends in the mitochondria.ends in the mitochondria.

It has the greatest energy production.It has the greatest energy production.

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Cont.Cont.

Plants make ATP during photosynthesis Plants make ATP during photosynthesis and use it to synthesize glucose and and use it to synthesize glucose and other carbohydrates.other carbohydrates.

But all organisms, plants included, can But all organisms, plants included, can make ATP by breaking down make ATP by breaking down carbohydrates, lipids, and proteins.carbohydrates, lipids, and proteins.

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Comparison of the main Comparison of the main types of energy releasing types of energy releasing pathwayspathways

ATP can be made by aerobic or anaerobic ATP can be made by aerobic or anaerobic mechanisms (with or without oxygen). mechanisms (with or without oxygen).

The first organisms on earth would have used The first organisms on earth would have used anaerobic respiration since O was not readily anaerobic respiration since O was not readily available. available.

Aerobic respiration is an efficient way to covert Aerobic respiration is an efficient way to covert glucose to ATPglucose to ATP

The pathways starts in the cytoplasm called The pathways starts in the cytoplasm called glycolysisglycolysis

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contcont

Glycolysis converts glucose to 2 pyruvate Glycolysis converts glucose to 2 pyruvate compoundscompounds

If oxygen is present then aerobic If oxygen is present then aerobic respiration proceeds - the pyruvate respiration proceeds - the pyruvate enters the mitochondria. If no oxygen is enters the mitochondria. If no oxygen is present the process stays in the present the process stays in the cytoplasm.cytoplasm.

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Overview of Aerobic Overview of Aerobic RespirationRespiration

More ATP is generated by aerobic More ATP is generated by aerobic respiration – yields 36 or morerespiration – yields 36 or more

Anaerobic respiration (without oxygen) Anaerobic respiration (without oxygen) has a very low yield and only yields 2 has a very low yield and only yields 2 ATP moleculesATP molecules

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Aerobic respiration steps:Aerobic respiration steps:

Step 1--Glycolysis in cytoplasm, take 2 Step 1--Glycolysis in cytoplasm, take 2 ATP to start then process; produces ATP to start then process; produces 2 pyruvates , electrons, hydrogen, 2 pyruvates , electrons, hydrogen, and produces 4 ATP – a net of 2 ATPand produces 4 ATP – a net of 2 ATP

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Step 2--Krebs cycle breaks down Step 2--Krebs cycle breaks down pyruvate to carbon dioxide, e- & H+, pyruvate to carbon dioxide, e- & H+, and and 2 ATP2 ATP. The Krebs cycle takes . The Krebs cycle takes place in the mitochondria.place in the mitochondria.

Step 3—Electron transfer Step 3—Electron transfer phosphorlation; membrane proteins phosphorlation; membrane proteins generate generate 32 ATP32 ATP, water by using , water by using oxygen as last e- acceptor. Takes oxygen as last e- acceptor. Takes place across membranes in the place across membranes in the mitochondria. mitochondria.

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Summary Equation for Summary Equation for Aerobic RespirationAerobic Respiration

CC66HH12120066 + 6O + 6O22 6CO6CO22 + 6H + 6H2200 glucose oxygen glucose oxygen carbon water carbon water

dioxidedioxide

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A simple sugarA simple sugar

(C(C66HH1212OO66))

Atoms held Atoms held together by together by covalent bondscovalent bonds

Glucose Glucose

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CYTOPLASM

Glycolysis

Electron Transfer

Phosphorylation

KrebsCycle ATP

ATP

2 CO2

4 CO2

2

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water

2 NADH

8 NADH

2 FADH2

2 NADH 2 pyruvate

e- + H+

e- + oxygen

(2 ATP net)

glucose

Typical Energy Yield: 36 ATP

e-

e- + H+

e- + H+

ATP

H+

e- + H+

ATP2 4

Glycolysis – Glycolysis – Glucose Breakdown StartsGlucose Breakdown Starts

Glycolysis is the first stage of aerobic Glycolysis is the first stage of aerobic respiration.respiration.

It is also the first stage in anaerobic It is also the first stage in anaerobic respiration, such as alcoholic and respiration, such as alcoholic and lactate (lactic acid) fermentation.lactate (lactic acid) fermentation.

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Importance of OxygenImportance of Oxygen

Electron transport phosphorylation Electron transport phosphorylation requires the presence of oxygenrequires the presence of oxygen

Oxygen withdraws spent electrons from Oxygen withdraws spent electrons from the electron transfer chain, then the electron transfer chain, then combines with Hcombines with H++ to form water to form water

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Fermentation PathwaysFermentation Pathways Without Oxygen or do not use oxygen – Without Oxygen or do not use oxygen –

anaerobicanaerobic Step 1 – Glycolysis in cytoplasmStep 1 – Glycolysis in cytoplasm

2 pyruvates2 pyruvates 2 Net ATP2 Net ATP 2 NADH2 NADH

Step 2 – FermentationStep 2 – Fermentation No more ATP is made only new end No more ATP is made only new end

productsproducts16

Alcoholic fermentationAlcoholic fermentation This pyruvic acid is then converted to CO2, ethanol, and This pyruvic acid is then converted to CO2, ethanol, and

energy for the cell. energy for the cell. Humans have long taken advantage of this process in Humans have long taken advantage of this process in

making bread, beer, and wine.making bread, beer, and wine. Yeast :Yeast :

in wheat & grains– in wheat & grains– sugar is converted into alcohol and carbon dioxide. sugar is converted into alcohol and carbon dioxide. The carbon dioxide will form bubbles, which will be The carbon dioxide will form bubbles, which will be

trapped by the gluten of the wheat causing the bread to trapped by the gluten of the wheat causing the bread to rise. rise.

small amounts of alcohol are formed, most of which will small amounts of alcohol are formed, most of which will be evaporated during the bread baking process. be evaporated during the bread baking process. Therefore, you won’t get drunk by eating bread! Therefore, you won’t get drunk by eating bread!

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Cont.Cont.

• In Grapes – In Grapes – produces ethanol at about 10% it kills yeast; produces ethanol at about 10% it kills yeast; Saccharomyces is responsible for the Saccharomyces is responsible for the

alcohol fermentation of wines. alcohol fermentation of wines. Grape juice contains naturally high levels of Grape juice contains naturally high levels of

sugars. sugars. These sugars are converted into alcohol and These sugars are converted into alcohol and

carbon dioxide.carbon dioxide.

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Lactate fermentationLactate fermentation

Ex. Food – Lactobacillus & other Ex. Food – Lactobacillus & other bacteria spoil food, some help make bacteria spoil food, some help make milk products; pickling –(sauerkraut)milk products; pickling –(sauerkraut)

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Ex. Muscles – ATP produced quickly, short termEx. Muscles – ATP produced quickly, short term     DURING EXERCISE, BREATHING CANNOT DURING EXERCISE, BREATHING CANNOT

PROVIDE YOUR BODY WITH ALL THE OXYGEN PROVIDE YOUR BODY WITH ALL THE OXYGEN IT NEEDS FOR AEROBIC RESPIRATION.  IT NEEDS FOR AEROBIC RESPIRATION. 

WHEN MUSCLES RUN OUT OF OXYGEN, THE WHEN MUSCLES RUN OUT OF OXYGEN, THE CELLS SWITCH TO LACTIC ACID CELLS SWITCH TO LACTIC ACID FERMENTATION. FERMENTATION.

Blood removes Lactic Acid from muscles, but if it is Blood removes Lactic Acid from muscles, but if it is not removed fast enough, the side effects of Lactic not removed fast enough, the side effects of Lactic Acid Fermentation is Muscle Fatigue, Pain, Cramps, Acid Fermentation is Muscle Fatigue, Pain, Cramps, and Soreness. and Soreness.

Most Lactic Acid made in the muscles diffuse into the Most Lactic Acid made in the muscles diffuse into the bloodstream, then to the LIVER, where it is bloodstream, then to the LIVER, where it is converted back to PYRUVIC ACID When Oxygen converted back to PYRUVIC ACID When Oxygen becomes Available. becomes Available.

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Lactate FermentationLactate Fermentation

C6H12O6

ATP

ATPNADH

2 lactate

electrons, hydrogen from NADH

2 NAD+

2

2 ADP

2 pyruvate

2

4

energy output

energy input

GLYCOLYSIS

LACTATE FORMATION

2 ATP net

Alterative Energy Sources in the Alterative Energy Sources in the BodyBody

When required, molecules other than When required, molecules other than glucose can enter the aerobic pathways glucose can enter the aerobic pathways as alternative energy sources.as alternative energy sources.

Cells must deal with too much or too little Cells must deal with too much or too little glucose.glucose.

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Fate of Glucose at mealtime & Fate of Glucose at mealtime & between Mealsbetween Meals

Glucose Glucose enter cell (at prompting of insulin) enter cell (at prompting of insulin) glucose-6-phosphate– trapped in cellglucose-6-phosphate– trapped in cell

If cells are not using up glucose rapidly it is If cells are not using up glucose rapidly it is converted to glycogen (polysaccharide) in the converted to glycogen (polysaccharide) in the liver & muscles of animalsliver & muscles of animals

Between meal glucose levels drop Between meal glucose levels drop pancreas secrete glucagonpancreas secrete glucagon converts converts glycogen in liver to glucose.glycogen in liver to glucose.

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Processes Are Linked Processes Are Linked

sunlight energy

water+

carbondioxide

PHOTOSYNTHESIS

AEROBICRESPIRATION

sugarmolecules

oxygen