Aerobic Respiration + Aerobic Respiration + The 1980s?The 1980s?

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7-2: Aerobic Respiration7-2: Aerobic Respiration

In most cells, In most cells, glycolysisglycolysis does not result in does not result in fermentation. fermentation.

Instead, if OInstead, if O22 is available, is available, pyruvic acid pyruvic acid

undergoes undergoes aerobic respirationaerobic respiration, or , or cellular respiration that requires Ocellular respiration that requires O22

Also known as Also known as oxidative respirationoxidative respiration

Overview of Aerobic RespirationOverview of Aerobic Respiration

Aerobic Respiration has 2 major stages:Aerobic Respiration has 2 major stages:1.1. Krebs CycleKrebs Cycle – oxidation of glucose is – oxidation of glucose is

completed; makes molecules of NADH; completed; makes molecules of NADH; produces a small amount of produces a small amount of ATPATP

2.2. Electron Transport Chain + Electron Transport Chain + Chemiosmosis Chemiosmosis – uses NADH to make – uses NADH to make ATPATP; ; produces most of the produces most of the ATPATP

Prokaryotes vs. EukaryotesProkaryotes vs. Eukaryotes In Prokaryotes, the reactions of the In Prokaryotes, the reactions of the Krebs Krebs

CycleCycle and and ETCETC takes place in the takes place in the cytosolcytosol of the cellof the cell

In Eukaryotes, the reactions of the In Eukaryotes, the reactions of the Krebs Krebs CycleCycle and and ETCETC takes place in the takes place in the mitochondriamitochondria Pyruvic acid Pyruvic acid diffuses across the membrane of diffuses across the membrane of

mitochondria into the mitochondria into the mitochondrial matrixmitochondrial matrix The matrix contains The matrix contains enzymesenzymes needed to needed to

catalyze the rxns of the Krebs cyclecatalyze the rxns of the Krebs cycle

Overview (cont.)Overview (cont.)

Pyruvic acidPyruvic acid reacts with a molecule called reacts with a molecule called Coenzyme ACoenzyme A to form to form acetyl CoAacetyl CoA COCO22 is given off and NAD is given off and NAD++ is reduced to is reduced to

NADHNADH

Stage I - Stage I - Krebs CycleKrebs Cycle Biochemical pathway that Biochemical pathway that

breaks down breaks down acetyl CoA acetyl CoA producing COproducing CO22, H atoms, + ATP, H atoms, + ATP AKA – AKA – TCA Cycle TCA Cycle or or Citric Acid Citric Acid

CycleCycle Identified + named after Identified + named after

German scientist Hans KrebGerman scientist Hans Kreb Reactions take place in the Reactions take place in the

mitochondrial matrixmitochondrial matrix

Krebs CycleKrebs Cycle (5 Steps) (5 Steps)

1.1. Acetyl CoAAcetyl CoA combines w/ a 4-C combines w/ a 4-C compound, compound, oxaloacetic acidoxaloacetic acid to produce to produce a 6-C compound, a 6-C compound, citric acidcitric acid. .

Reaction regenerates coenzyme AReaction regenerates coenzyme A

Krebs CycleKrebs Cycle

2.2. Citric acid Citric acid releases a COreleases a CO22 and H to form and H to form

a 5-C compounda 5-C compound Citric acid gets oxidizedCitric acid gets oxidized H atom transfers to NADH atom transfers to NAD++ - - NAD - - NAD++ reduced reduced

to NADHto NADH

Krebs CycleKrebs Cycle

3.3. The 5-C compound releases a COThe 5-C compound releases a CO22

molecule and H to form a 4-C compoundmolecule and H to form a 4-C compound NADNAD++ is reduced to NADH is reduced to NADH ATPATP created from ADP created from ADP

Krebs CycleKrebs Cycle4.4. The 4-C compound releases a H atom to The 4-C compound releases a H atom to

form another 4-C compoundform another 4-C compound H transferred to FAD (accepts eH transferred to FAD (accepts e-- during during

redox)redox)• FAD gets reduced to FADHFAD gets reduced to FADH22

Krebs CycleKrebs Cycle5.5. The 4-C compound releases a H atom to The 4-C compound releases a H atom to

regenerate regenerate oxaloacetic acidoxaloacetic acid, which , which keeps the keeps the Krebs cycle Krebs cycle goinggoing

NADNAD++ reduced to NADH reduced to NADH

Krebs CycleKrebs Cycle

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What’s been accomplished thus far…What’s been accomplished thus far…

One One glucoseglucose molecule = 2 molecule = 2 pyruvic acid pyruvic acid molecules = 2 molecules = 2 acetyl CoA acetyl CoA molecules = 2 molecules = 2 turns of turns of Krebs CycleKrebs Cycle

These turns produce:These turns produce: 6 NADH6 NADH 2 FADH2 FADH22

2 2 ATPATP 4 CO4 CO22

NOT ENOUGH ENERGY TO LIVE OFF NOT ENOUGH ENERGY TO LIVE OFF OF…OF…

So what now?So what now? Use our energy-carrying moleculesUse our energy-carrying molecules

• NADH + FADHNADH + FADH22

• Total # of Molecules:Total # of Molecules: 10 NADH (2 – Gly; 2 – PA to Acetyl CoA; 10 NADH (2 – Gly; 2 – PA to Acetyl CoA;

6 – Krebs)6 – Krebs) 2 FADH2 FADH22 (2 – Krebs) (2 – Krebs)

Take them and go to next stage of AR……Take them and go to next stage of AR……• THE ELECTRON TRANSPORT CHAINTHE ELECTRON TRANSPORT CHAIN

Stage II – Stage II – ETC + ChemiosmosisETC + Chemiosmosis Series of molecules that transfer electrons Series of molecules that transfer electrons

from one molecule to anotherfrom one molecule to another In Eukaryotes, the In Eukaryotes, the ETCETC takes place in the takes place in the

inner membrane of mitochondriainner membrane of mitochondria In Prokaryotes, the In Prokaryotes, the ETCETC takes place in the takes place in the

cell membranecell membrane ATPATP is produced by ETC when NADH + FADH is produced by ETC when NADH + FADH22

release H atomsrelease H atoms

THE ELECTRON TRANSPORT CHAINTHE ELECTRON TRANSPORT CHAIN((5 Steps5 Steps))

1.1. NADH + FADHNADH + FADH22 donate electrons to the donate electrons to the

ETC. They also donate protons (HETC. They also donate protons (H++)) NADH – 3 eNADH – 3 e--

FADHFADH22 – 2 e – 2 e--

• NADH = 10 * 3 = 30 total e-

• FADH2 = 2 * 2 = 4 total e-

ETC (cont.)ETC (cont.)2.2. The eThe e-- are passed along a chain from are passed along a chain from

molecule to molecule in a series of redox molecule to molecule in a series of redox reactions. As they are passed, they lose reactions. As they are passed, they lose energy.energy.

ETC (cont.)ETC (cont.)3.3. The energy lost by electrons are used to The energy lost by electrons are used to

pump protons from the matrix outside the pump protons from the matrix outside the inner mitochondrial membrane (cristae). inner mitochondrial membrane (cristae). A A concentrationconcentration gradientgradient and and electricalelectrical gradientgradient are created. are created.

ETC (cont.)ETC (cont.)4.4. The concentration + electrical gradients The concentration + electrical gradients

drive the synthesis of drive the synthesis of ATPATP by by ChemiosmosisChemiosmosis. As protons move through . As protons move through molecules of ATP synthase, molecules of ATP synthase, ATPATP is made is made from ADP + phosphatefrom ADP + phosphate

ETC (cont.)ETC (cont.)5.5. The final acceptor of electrons is The final acceptor of electrons is oxygenoxygen. .

It also accepts protons and combines to It also accepts protons and combines to make molecules of make molecules of waterwater

ETC (cont.)ETC (cont.) NoteNote: If electrons weren’t : If electrons weren’t

able to be picked up by able to be picked up by oxygen at the end of the oxygen at the end of the ETC chain, the entire ETC chain, the entire process of chemiosmosis process of chemiosmosis would stop!would stop!

NO NO ATPATP MADE MADE FOR CELLS TO FOR CELLS TO DO WORKDO WORK

Efficiency of Cellular RespirationEfficiency of Cellular Respiration

ATPsATPs produced ~ produced ~ 3838 Actually get only 36 Actually get only 36 ATPsATPs due to active due to active

transport of NADH molecules across cristae of transport of NADH molecules across cristae of mitochondriamitochondria

Cellular Respiration Efficiency ~ Cellular Respiration Efficiency ~ 39%39% 20x more efficient that glycolysis alone20x more efficient that glycolysis alone More efficient than most machines (25%)More efficient than most machines (25%) Some energy lost as Some energy lost as heatheat

Energy Yield of Energy Yield of Cellular RespirationCellular Respiration

What is the equation for the complete What is the equation for the complete oxidation of glucose?oxidation of glucose?

CC66HH1212OO66 + 6O + 6O22 -----> 6CO -----> 6CO22 + +

6H6H220 + 0 + energyenergy ( (heatheat and and

ATPATP))

In addition to glucose, In addition to glucose, other compounds other compounds can be broken down by cells as a can be broken down by cells as a source source of fuelof fuel. They can also enter Glycolysis . They can also enter Glycolysis and/or the Krebs Cycle at any time to yield and/or the Krebs Cycle at any time to yield more energy to an organism.more energy to an organism.

WhatWhat areare thesethese otherother compoundscompounds?? FATSFATS PROTEINSPROTEINS CARBOHYDRATESCARBOHYDRATES

Why isn’t CR the reverse of Why isn’t CR the reverse of Photosynthesis?Photosynthesis?

Involve different biochemical reactionsInvolve different biochemical reactions P – Light Rxns (ETC/Chemiosmosis) + P – Light Rxns (ETC/Chemiosmosis) +

Calvin CycleCalvin Cycle CR – Glycolysis, Krebs Cycle,+ CR – Glycolysis, Krebs Cycle,+

ETC/ChemiosmosisETC/Chemiosmosis Occur at different sites in cellsOccur at different sites in cells

P – ChloroplastsP – Chloroplasts CR - MitochondriaCR - Mitochondria

Functions of CRFunctions of CR MajorMajor::

CR provides the CR provides the ATPATP that all cells need to that all cells need to support the activities of lifesupport the activities of life• Body uses Body uses 100,000,000,000,000,000,000100,000,000,000,000,000,000 (1x10 (1x102020) )

ATP each secondATP each second

MinorMinor:: Building of macromoleculesBuilding of macromolecules

• Can’t get them from food – so must be made Can’t get them from food – so must be made from compounds in Glycolysis + Krebs Cyclefrom compounds in Glycolysis + Krebs Cycle

C.R. videoC.R. video

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