California Science Standards #1f, 1g, 1i, 6d, 9a

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Cellular RespirationCellular Respiration

Extracting energy from Organic compounds (food)

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What do we know?What do we know?Photosynthesis

– Occurs in autotrophs– Stores ENERGY– Produces glucose

– CO2 + H2O C6H12O6 + O2

Cellular respiration– Occurs in autotrophs and heterotrophs– Releases ENERGY– Uses glucose

– C6H12O6 + O2 CO2 + H20

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Respiration is a combustion reactionRespiration is a combustion reaction Like the burning snack

foods, the “burning” of food molecules (glucose) in cells produces CO2 and H20, and it is an exothermic process.

•In exothermic reactions, the reactants contain more energy before the reaction than the products contain at the end of the reaction. (i.e: energy is released.)

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Some key differencesSome key differences

In the lab, the combustion released energy as heat (which increased the temp of the water in the test tube). This reaction occurred very quickly.– A cell cannot use heat

to do cellular work, not to mention the fact that this large increase in temp would be dangerous!

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Respiration “slows down” the Respiration “slows down” the combustion of glucosecombustion of glucose

The energy from glucose is released slowly by many enzyme-catalyzed reactions during cell respiration. This released energy is used to make ATP.

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Respiration uses energy stored in Respiration uses energy stored in glucose to make ATPglucose to make ATP

ATP is adenosine triphosphate and is the main stored form of energy in all cells

ATP contains three phosphate groups (see pic: the negative charges repel one another so the ATP is “unstable”). When one is removed, energy is released.

The released energy from ATP is used for cellular work.

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ATP: The energy “currency” of a ATP: The energy “currency” of a cell.cell.

All cellular work comes at the “expense” of ATP.

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Cellular RespirationCellular RespirationAn Overview (“Map”)

ATP

ATP

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GlycolysisGlycolysisFirst step of cellular respiration; occurs in

the cytoplasm.Breaks apart 1 glucose molecule (6-C) into

2 pyruvic acid molecules (3-C each)Requires glucose and 2 ATP Produces pyruvic acid /pyruvate, NADH,

and 2 ATP (net yield)– Pyruvic acid used later in Krebs cycle– NADH (transports electrons) used in electron

transport chain (ETC)

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Glucose

6-carbon compound

2 moleculesof PGAL

2 molecules of 3-C compound

2 moleculesof pyruvic acid

STEP 1

STEP 2

STEP 3

STEP 4

C C C C C C

C C C C C C PP

C C CP C C C P

C C CP P C C CP P

C C C C C C

-2 ATP

2 NADH

4 ATP

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Cellular RespirationCellular RespirationCheck the Map…

ATP

ATP

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Aerobic Respiration (one branch Aerobic Respiration (one branch of cellular respiration)of cellular respiration)

Requires oxygen Produces nearly 20x more ATP than is produced

by glycolysis alone 2 major stages:

– Krebs cycle– Electron transport chain

Location: Mitochondria Begins with pyruvic acid that is modified to

become acetyl-CoA

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Krebs CycleKrebs CycleOccurs in the mitochondrial matrixAcetyl CoA binds to oxaloacetic acid

producing citric acid.In reactions, the hydrogens are “stripped”

off the organic compounds, releasing carbons as CO2 (waste).

Produces CO2, NADH, FADH2, and 2 ATP

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Citric acid

C C C C C C

Oxaloaceticacid

C C C C

C C

4-C compound

C C C C

C

ATP

NADH

5-C compound

C C C C C

C

NADH

NADH

4-C compound

C C C CFADH2

Krebs Krebs CycleCycle

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Electron Transport ChainElectron Transport Chain

Last stage of aerobic respirationLocated on inner membrane folds (cristae)

of mitochondrioncristae

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Electron transport chain is here

(Mitochondrial Matrix-

Location of R&P of Krebs Cycle)

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a.k.a ATP synthase

(ETS)

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Electron Transport, continuedElectron Transport, continued

NADH and FADH2 contain high energy electrons.

When NADH and FADH2 reach the ETC they lose H+ and e-. Their high-energy e- are passed along the ETC, and energy from the e- is used to pump H+ (protons) to the outer compartment of the mitochondrion.

Energy from diffusion of H+ back into the matrix is used to generate 34 ATP molecules (chemiosmosis)

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ATP Synthase

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Let’s Review the Summary Let’s Review the Summary EquationEquation

C6H12O6 + O2 CO2 + H20– Glucose used in glycolysis– CO2 produced in Krebs cycle (completing the breakdown of

glucose) What is the importance of Oxygen?

– There must be a “final acceptor” of e- at the end of the ETC. If the last protein in the chain holds onto the e- there will be a “traffic jam” and no other e- will flow down the chain.

– Result: H+ pumping stops, so H+ gradient disappears and there is no energy to drive the synthesis of ATP.

– Oxygen is the final e- acceptor of the ETC, so it keeps the ETC “running”.

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So oxygen is used in the ETC and this is where water is formed.– When oxygen accepts the e-, it also bonds with

H+ to form H2O.

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Total ATP From Cellular Total ATP From Cellular RespirationRespiration

34

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Cellular RespirationCellular RespirationCheck the Map…

ATP

ATP

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Fermentation Fermentation (Anaerobic Respiration)(Anaerobic Respiration)

No oxygen? No problem…(kind of) 2 types: lactic acid fermentation,

alcoholic fermentation Pros: can regenerate NAD+ when short on O2

– Keeps glycolysis going (small net gain of ATP) Cons: Cannot produce additional ATP

– Only unicellular organisms, like bacteria or yeast, can survive with the ATP made by glycolysis alone.

– Some cells in multicellular organisms can switch to anaerobic respiration, but only for a short time.

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Lactic Acid FermentationLactic Acid Fermentation Manufacture of yogurt, cheese Muscle cells

– “Anaerobic exercise” (sprints)– Lactic acid build-up (muscle burn, fatigue, cramps)

Pyruvic acid

Lactic acid

Glucose

C C C C C C C C C

C C C

NAD+ NADH + H+

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Alcoholic FermentationAlcoholic FermentationBasis of wine and beer industries

– Yeast + fruit juice = alcohol

Takes place when making bread– CO2 makes bread rise; alcohol evaporates

Pyruvic acid

Ethyl alcohol

Glucose

C C C C C C C C C

C C

NAD+ NADH + H+

2-C compound

C C

CCO2