CHAPTER 9 CELLULAR RESPIRATION. ENERGY HARVEST FERMENTATION- the partial breaking-down of sugars that occurs without the help of oxygen CELLULAR RESPIRATION-

CHAPTER 9CHAPTER 9

CELLULAR RESPIRATIONCELLULAR RESPIRATION

ENERGY HARVESTENERGY HARVEST

FERMENTATION- the partial breaking-FERMENTATION- the partial breaking-down of sugars that occurs without the down of sugars that occurs without the help of oxygenhelp of oxygen

CELLULAR RESPIRATION- CELLULAR RESPIRATION- oxygen is oxygen is consumed as a reactant along with consumed as a reactant along with organic fuel organic fuel

Organic compounds + oxygen Organic compounds + oxygen carbon dioxide + water + energy carbon dioxide + water + energy

oror

CC66HH1212OO66 + 6 O + 6 O22 6 H 6 H22O + 6COO + 6CO22+ Energy+ Energy

CC66HH1212OO6 6 = glucose= glucose

- - the breakdown of glucose is the breakdown of glucose is exergonic; exergonic; ΔΔG is negativeG is negative

RECALL ATP:RECALL ATP:

ATP= adenosine triphosphate ATP= adenosine triphosphate

- triphosphate tail of ATP is like a loaded - triphosphate tail of ATP is like a loaded springspring

- - spring is relaxed by removing the spring is relaxed by removing the last phosphatelast phosphate

- cells tap this energy by using enzymes - cells tap this energy by using enzymes to transfer phosphate groups from ATP to transfer phosphate groups from ATP to other compoundsto other compounds

PHOSPHORYLATION!PHOSPHORYLATION!

- when energy is used, ATP is converted - when energy is used, ATP is converted to ADP, which stores less energyto ADP, which stores less energy

- - to keep working, a cell must to keep working, a cell must regenerate ATPregenerate ATP

OXIDATION- REDUCTION OXIDATION- REDUCTION REACTIONSREACTIONS

The transfer of electrons during chemical The transfer of electrons during chemical reactions releases energy stored in food reactions releases energy stored in food molecules, and this energy is used to molecules, and this energy is used to synthesize ATPsynthesize ATP

- Redox reactions- reactions in which there - Redox reactions- reactions in which there is a transfer of one or more electrons (e-) is a transfer of one or more electrons (e-) from one reactant to anotherfrom one reactant to another

OXIDATION- OXIDATION- the loss of electrons from the loss of electrons from one substanceone substance

REDUCTION- REDUCTION- the addition of the addition of electrons to another substanceelectrons to another substance

Ex: XeEx: Xe-- + Y + Y X + Ye X + Ye--

X- the electron donor, is called the X- the electron donor, is called the REDUCING AGENT; it reduces YREDUCING AGENT; it reduces Y

Y- the electron acceptor, is called the Y- the electron acceptor, is called the OXIDIZING AGENT; it oxidizes XOXIDIZING AGENT; it oxidizes X

THESE REACTIONS ALWAYS OCCUR THESE REACTIONS ALWAYS OCCUR TOGETHER!TOGETHER!

- sometimes electrons are not COMPLETELY - sometimes electrons are not COMPLETELY transferred from one substance to transferred from one substance to another; the degree of sharing in covalent another; the degree of sharing in covalent bonds is changedbonds is changed

- - electrons may be pulled toward a electrons may be pulled toward a more electronegative atom; this more electronegative atom; this atom is reducedatom is reduced

- energy must be added to pull an electron - energy must be added to pull an electron away from an atom (like energy must be away from an atom (like energy must be added to push a large ball uphill)added to push a large ball uphill)

- the more electronegative an atom, - the more electronegative an atom, the more energy is required to keep the more energy is required to keep electrons away from itelectrons away from it

- a redox reaction that relocates - a redox reaction that relocates electrons to a more electronegative electrons to a more electronegative atom (like oxygen) releases chemical atom (like oxygen) releases chemical energy that can be put to workenergy that can be put to work

ELECTRONS “FALL” FROM ELECTRONS “FALL” FROM ORGANIC MOLECULES ORGANIC MOLECULES DURING RESPIRATIONDURING RESPIRATION

Think of the equation for cellular respiration as Think of the equation for cellular respiration as a redox process:a redox process:

OxdiationOxdiation

CC66HH1212OO66 + 6O + 6O22 6CO 6CO22 + 6H + 6H22OO

ReductionReduction

Glucose is oxidized, oxygen is reduced, Glucose is oxidized, oxygen is reduced, electrons lose potential energy along the wayelectrons lose potential energy along the way

- - electrons are pulled toward oxygenelectrons are pulled toward oxygen

- in general, organic compounds with a lot - in general, organic compounds with a lot of hydrogen atoms are good as fuels of hydrogen atoms are good as fuels because their bonds are a source of e- because their bonds are a source of e- that can “fall” closer to oxygenthat can “fall” closer to oxygen

- In cellular respiration, as hydrogen is - In cellular respiration, as hydrogen is transferred to oxygen, electrons are also transferred to oxygen, electrons are also transferred, releasing energytransferred, releasing energy

- by oxidizing glucose, respiration is taking - by oxidizing glucose, respiration is taking energy out of storage and using it to energy out of storage and using it to make ATPmake ATP

THE “FALL” OF ELECTRONS THE “FALL” OF ELECTRONS IS STEPWISEIS STEPWISE

Glucose and other organic fuels are broken Glucose and other organic fuels are broken down gradually in a series of steps, each down gradually in a series of steps, each catalyzed by an enzymecatalyzed by an enzyme

- - at certain steps, hydrogen atoms are at certain steps, hydrogen atoms are taken away from glucose, but not taken away from glucose, but not transferred directly to oxygentransferred directly to oxygen

- they are first passed to an enzyme called - they are first passed to an enzyme called NADNAD++ (nicotinamide adenine dinucleotide) (nicotinamide adenine dinucleotide)

- NAD- NAD++ functions as an oxidizing agent (e- functions as an oxidizing agent (e- acceptor) during respirationacceptor) during respiration

HOW DOES NADHOW DOES NAD++ TRAP e- TRAP e- FROM GLUCOSE?FROM GLUCOSE?

- Enzymes called dehydrogenases remove 2 - Enzymes called dehydrogenases remove 2 hydrogen atoms from the glucosehydrogen atoms from the glucose

- can think of this as removing 2 electrons can think of this as removing 2 electrons and 2 protons and 2 protons

- - - the enzyme delivers the 2 electrons the enzyme delivers the 2 electrons and 1 proton to NADand 1 proton to NAD++ (other proton is (other proton is released to the surrounding solution)released to the surrounding solution)

- NADH is the reduced form- electrons have - NADH is the reduced form- electrons have been picked up been picked up

- each NADH molecule represents stored - each NADH molecule represents stored energy that can be tapped to make ATP energy that can be tapped to make ATP when electrons “fall” from NADH to when electrons “fall” from NADH to oxygenoxygen

HOW DO ELECTRONS “FALL” TO OXYGEN?HOW DO ELECTRONS “FALL” TO OXYGEN?

- respiration uses an electron transport - respiration uses an electron transport chain to break the fall of electrons to chain to break the fall of electrons to oxygen into several energy-releasing oxygen into several energy-releasing stepssteps

ELECTRON TRANSPORT CHAIN- consists of a ELECTRON TRANSPORT CHAIN- consists of a number of molecules, mostly proteins, built into number of molecules, mostly proteins, built into the inner membrane of the mitochondrionthe inner membrane of the mitochondrion

- - electrons removed from glucose are electrons removed from glucose are shuttled by NADH to the “top” of the shuttled by NADH to the “top” of the chainchain

- at the bottom end, oxygen captures these - at the bottom end, oxygen captures these electrons along with hydrogen ions forming electrons along with hydrogen ions forming waterwater

- - this process is exergonicthis process is exergonic

- instead of energy being released and wasted - instead of energy being released and wasted in a single explosive step, electrons cascade in a single explosive step, electrons cascade down the chain from one carrier molecule to down the chain from one carrier molecule to the next, losing a small amount of energy the next, losing a small amount of energy with each stepwith each step

- each carrier is more electronegative than its - each carrier is more electronegative than its uphill neighbor, so electrons keep moving uphill neighbor, so electrons keep moving down the chain to oxygen (the most down the chain to oxygen (the most electronegative)electronegative)

- compared to gravity pulling objects downhill- compared to gravity pulling objects downhill

SUMMARYSUMMARY

Electrons follow this “downhill” route:Electrons follow this “downhill” route:

Food Food NADH NADH electron transport electron transport chain chain oxygen oxygen

NEXT: How does the cell use the NEXT: How does the cell use the energy released from this electron energy released from this electron fall to regenerate ATP?fall to regenerate ATP?

PROCESS OF PROCESS OF CELLULAR CELLULAR

RESPIRATIONRESPIRATION

http://www.kathleensworld.com/mitochondria.jpghttp://www.kathleensworld.com/mitochondria.jpg

3 STAGES:3 STAGES:

1. Glycolysis1. Glycolysis

2. Krebs Cycle2. Krebs Cycle

3. Electron transport chain and oxidative 3. Electron transport chain and oxidative phosphorylationphosphorylation

- Glycolysis and the Krebs cycle are - Glycolysis and the Krebs cycle are pathways that DECOMPOSE glucosepathways that DECOMPOSE glucose

GLYCOLYSIS- GLYCOLYSIS- occurs in cytosol, breaks occurs in cytosol, breaks down glucose into 2 molecules of down glucose into 2 molecules of pyruvatepyruvate

KREBS CYCLE- KREBS CYCLE- Takes place in Takes place in mitochondrial matrix; decomposes a mitochondrial matrix; decomposes a form of pyruvate to COform of pyruvate to CO22

- in the third stage of respiration, the electron - in the third stage of respiration, the electron transport chain accepts electrons from the transport chain accepts electrons from the breakdown of products from the first 2 breakdown of products from the first 2 stages, and passes electrons from one stages, and passes electrons from one molecule to anothermolecule to another

- - at the end of the chain, H+ and Oat the end of the chain, H+ and O22 combine to make watercombine to make water

- the energy released at each step of the - the energy released at each step of the chain is stored in a form that the chain is stored in a form that the mitochondrion can use to make ATPmitochondrion can use to make ATP

- this is called OXIDATIVE - this is called OXIDATIVE PHOSPHORYLATION because it is powered PHOSPHORYLATION because it is powered by the redox reactions that transfer by the redox reactions that transfer electrons from food to oxygenelectrons from food to oxygen

- - oxidative phosphorylation accounts oxidative phosphorylation accounts for 90% of the ATP made by for 90% of the ATP made by respirationrespiration

- A small amount of ATP is made directly by - A small amount of ATP is made directly by glycolysis and the Krebs cycle- called glycolysis and the Krebs cycle- called SUBSTRATE-LEVEL PHOSPHORYLATIONSUBSTRATE-LEVEL PHOSPHORYLATION

- - occurs when an enzyme transfers a occurs when an enzyme transfers a phosphate group from a substrate phosphate group from a substrate molecule to ADPmolecule to ADP

For each molecule of glucose broken down For each molecule of glucose broken down into COinto CO22 during respiration, the cell makes during respiration, the cell makes up to 38 molecules of ATPup to 38 molecules of ATP

GLYCOLYSISGLYCOLYSIS

Glycolysis Glycolysis means “splitting of sugar”, means “splitting of sugar”, and that is what happens in this and that is what happens in this pathwaypathway

- Glucose (6-carbon) is split into two - Glucose (6-carbon) is split into two three-carbon sugarsthree-carbon sugars

- - these sugars are oxidized, and these sugars are oxidized, and form 2 molecules of pyruvateform 2 molecules of pyruvate

Glycolysis is made up of 10 steps, each Glycolysis is made up of 10 steps, each step catalyzed by a specific enzymestep catalyzed by a specific enzyme

- The steps can be divided into 2 phases:- The steps can be divided into 2 phases:

ENERGY INVESTMENT PHASE- first 5 steps; ENERGY INVESTMENT PHASE- first 5 steps; cell spends ATP to phosphorylate the cell spends ATP to phosphorylate the fuel moleculesfuel molecules

ENERGY PAYOFF PHASE- ATP is produced ENERGY PAYOFF PHASE- ATP is produced by substrate-level phosphorylation, by substrate-level phosphorylation, NAD+ is reduced to NADHNAD+ is reduced to NADH

NET YIELD = NET YIELD = 2 ATP plus 2 NADH2 ATP plus 2 NADH

- glycolysis occurs with or without - glycolysis occurs with or without oxygenoxygen

- - Krebs cycle and Electron Krebs cycle and Electron transport chain do need oxygentransport chain do need oxygen

Figure 9.9 A closer look at glycolysis: energy investment phase (Layer 2)Figure 9.9 A closer look at glycolysis: energy investment phase (Layer 2)

Figure 9.9 A closer look at glycolysis: energy payoff phase (Layer 4)Figure 9.9 A closer look at glycolysis: energy payoff phase (Layer 4)

KREBS CYCLEKREBS CYCLE

IF MOLECULAR OXYGEN IS PRESENT:IF MOLECULAR OXYGEN IS PRESENT:

- - the 2 pyruvates enter the Krebs the 2 pyruvates enter the Krebs cycle (in the mitochondrion)cycle (in the mitochondrion)

- enzymes complete the oxidation of - enzymes complete the oxidation of the organic fuelthe organic fuel

PREPARING FOR KREBS PREPARING FOR KREBS CYCLECYCLE

- When the 3-carbon pyruvate enters the - When the 3-carbon pyruvate enters the mitochondria, it is converted to the 2-mitochondria, it is converted to the 2-carbon acetatecarbon acetate

- - the extra carbon from pyruvate is the extra carbon from pyruvate is released as COreleased as CO22 (first step in (first step in respiration where COrespiration where CO22 is released) is released)

- another NADH molecule is produced, - another NADH molecule is produced, and it heads to the electron transport and it heads to the electron transport chain to help make more ATPchain to help make more ATP

- the acetate attaches to a coenzyme - the acetate attaches to a coenzyme called called coenzyme A coenzyme A to form the to form the compound compound acetyl-CoAacetyl-CoA

- the acetyl-CoA then enters the Krebs - the acetyl-CoA then enters the Krebs cyclecycle

Into the Krebs CycleInto the Krebs Cycle

- has 8 steps, each catalyzed by a - has 8 steps, each catalyzed by a specific enzymespecific enzyme

- in the Krebs Cycle, 2 carbons enter in - in the Krebs Cycle, 2 carbons enter in the form of acetate, and 2 different the form of acetate, and 2 different carbons leave in the form of COcarbons leave in the form of CO22

- most energy harvested in the Krebs - most energy harvested in the Krebs cycle is in the form of NADH (for each cycle is in the form of NADH (for each acetate, 3 molecules of NADH are acetate, 3 molecules of NADH are made)made)

- - there is an additional electron there is an additional electron acceptor called FAD (flavin acceptor called FAD (flavin adenine dinucleotide)adenine dinucleotide)

- the reduced form, FADH- the reduced form, FADH22 donates its donates its electrons along with NADH to the electrons along with NADH to the electron transport chainelectron transport chain

- - some ATP is also formedsome ATP is also formed

ELECTRON ELECTRON TRANSPORTTRANSPORT

So far, we have only seen the production So far, we have only seen the production of 4 ATPs from glycolysis and the Krebs of 4 ATPs from glycolysis and the Krebs cycle for each glucose moleculecycle for each glucose molecule

- 2 from each- 2 from each

- - NADH and FADHNADH and FADH22 account for most account for most of the energy extracted from foodof the energy extracted from food

- these molecules link glycolysis and the - these molecules link glycolysis and the Krebs Cycle to oxidative Krebs Cycle to oxidative phosphorylationphosphorylation

PATHWAY OF ELECTRON PATHWAY OF ELECTRON TRANSPORTTRANSPORT

RECALL: Electron transport chain is a RECALL: Electron transport chain is a collection of molecules embedded in the collection of molecules embedded in the inner membrane of the mitochondrioninner membrane of the mitochondrion

- the cristae provides space for thousands - the cristae provides space for thousands of these chains in each mitochondrionof these chains in each mitochondrion

The chain is made up of proteins and The chain is made up of proteins and nonprotein components essential for the nonprotein components essential for the function of enzymesfunction of enzymes

- during electron transport, these - during electron transport, these nonprotein components alternate nonprotein components alternate between reduced and oxidized states between reduced and oxidized states as they accept and donate electronsas they accept and donate electrons

- electrons removed from food during - electrons removed from food during glycolysis and the Krebs cycle are glycolysis and the Krebs cycle are transferred by NADH to the first transferred by NADH to the first molecule of the electron transport molecule of the electron transport chainchain

- - this first electron acceptor is a this first electron acceptor is a flavoprotein flavoprotein

- this flavoprotein returns to its - this flavoprotein returns to its oxidized form as it passes electrons oxidized form as it passes electrons to an iron-sulfur proteinto an iron-sulfur protein

- electrons are then passed to a - electrons are then passed to a compound called ubiquinone (a lipid)compound called ubiquinone (a lipid)

- most of the next electron carriers are - most of the next electron carriers are called called cytochromes cytochromes (iron-containing (iron-containing compounds)compounds)

- the last cytochrome of the chain passes - the last cytochrome of the chain passes its electrons to oxygenits electrons to oxygen

- - oxygen picks up a pair of hydrogen oxygen picks up a pair of hydrogen ions from the solution to form waterions from the solution to form water

- FADH- FADH22 also adds electrons to the chain, also adds electrons to the chain, but at a lower energy levelbut at a lower energy level

- because of this, the electron transport - because of this, the electron transport chain will produce about 1/3 less energy chain will produce about 1/3 less energy for ATP synthesis when the electron donor for ATP synthesis when the electron donor is FADHis FADH22

- - the electron transport chain does not the electron transport chain does not make ATP DIRECTLY; it allows energy make ATP DIRECTLY; it allows energy to be released in smaller amountsto be released in smaller amounts

HOW DOES THE CELL COUPLE THIS ENERGY HOW DOES THE CELL COUPLE THIS ENERGY RELEASE TO ATP SYNTHESIS?RELEASE TO ATP SYNTHESIS?

CHEMIOSMOSISCHEMIOSMOSIS

Within the inner membrane of the Within the inner membrane of the mitochondrion, there is a protein complex mitochondrion, there is a protein complex called called ATP SYNTHASEATP SYNTHASE

- this protein uses a proton gradient to drive - this protein uses a proton gradient to drive ATP synthesis (power source for ATP ATP synthesis (power source for ATP synthesis is a difference in the synthesis is a difference in the concentration of H+ on opposite sides of concentration of H+ on opposite sides of the inner mitochondrial membrane)the inner mitochondrial membrane)

- the electron transport chain plays an - the electron transport chain plays an important roleimportant role

STEPS OF CHEMIOSMOSISSTEPS OF CHEMIOSMOSIS

1. The electron transport chain uses the 1. The electron transport chain uses the exergonic flow of electrons to pump exergonic flow of electrons to pump H+ across the membrane (from the H+ across the membrane (from the matrix to the intermembrane space)matrix to the intermembrane space)

2. The H+ leak back across the 2. The H+ leak back across the membrane, diffusing down their membrane, diffusing down their gradient (high to low)gradient (high to low)

- - the ATP Synthases are the only the ATP Synthases are the only places freely permeable to H+places freely permeable to H+

3. The ions pass through a channel in 3. The ions pass through a channel in ATP synthase, and this protein uses ATP synthase, and this protein uses the energy (from diffusion of H+) to the energy (from diffusion of H+) to drive the oxidative phosphorylation drive the oxidative phosphorylation of ADP, of ADP, MAKING ATPMAKING ATP

**NOTE- though this is called **NOTE- though this is called chemiosmosis, it does NOT have chemiosmosis, it does NOT have anything to do with water transportanything to do with water transport

SOME UNANSWERED SOME UNANSWERED QUESTIONS…QUESTIONS…

““HOW DOES THE ELECTRON TRANSPORT CHAIN HOW DOES THE ELECTRON TRANSPORT CHAIN PUMP HYDROGEN IONS?”PUMP HYDROGEN IONS?”

““HOW DOES ATP SYNTHASE USE H+ BACKFLOW HOW DOES ATP SYNTHASE USE H+ BACKFLOW TO MAKE ATP”?TO MAKE ATP”?

- - certain members of the chain accept and certain members of the chain accept and release protons (H+) along with electronsrelease protons (H+) along with electrons

- at certain steps, electron transfers cause H+ to - at certain steps, electron transfers cause H+ to be taken up and then released into the solution be taken up and then released into the solution (intermembrane space)(intermembrane space)

- the H+ gradient is called - the H+ gradient is called PROTON-PROTON-MOTIVE FORCEMOTIVE FORCE

- - the force drives H+ back across the force drives H+ back across the membrane through ATP the membrane through ATP synthase channelssynthase channels

THIS MECHANISM IS ALSO SEEN IN THIS MECHANISM IS ALSO SEEN IN PHOTOSYNTHESIS!PHOTOSYNTHESIS!

CELL RESPIRATION- A CELL RESPIRATION- A SUMMARYSUMMARY

During respiration, energy flows:During respiration, energy flows:

Glucose > NADH > Electron transport Glucose > NADH > Electron transport chain > proton-motive force > ATPchain > proton-motive force > ATP

Glycolysis and Krebs cycle produce only Glycolysis and Krebs cycle produce only about 2 ATPs each (total 4)about 2 ATPs each (total 4)

Oxidative Phosphorylation produces a Oxidative Phosphorylation produces a maximum of 34 ATPsmaximum of 34 ATPs

TOTAL = 38 ATPs (only an TOTAL = 38 ATPs (only an estimate)estimate)

EFFICIENCY OF EFFICIENCY OF RESPIRATIONRESPIRATIONWHAT % OF CHEMICAL ENERGY STORED IN WHAT % OF CHEMICAL ENERGY STORED IN

GLUCOSE IS RESTOCKED IN ATP?GLUCOSE IS RESTOCKED IN ATP?

-The oxidation of a mole of glucose releases -The oxidation of a mole of glucose releases 686 kcal of energy686 kcal of energy

- Phosphorylation of ADP to form ATP - Phosphorylation of ADP to form ATP stores stores at at least 7.3 kcal per moleleast 7.3 kcal per mole

Efficiency = 7.3 X 38(max ATP)Efficiency = 7.3 X 38(max ATP)------------------------------------------- =------------------------------------------- = 40% 40%

686686

- the rest is lost as heat- the rest is lost as heat

COMPARE:COMPARE:

The most efficient automobile converts The most efficient automobile converts only about 25% of the energy stored only about 25% of the energy stored in gasoline to move the carin gasoline to move the car

OTHER METABOLIC OTHER METABOLIC PROCESSESPROCESSES

FERMENTATIONFERMENTATIONRECALL GLYCOLYSIS:RECALL GLYCOLYSIS:

Glucose is oxidized into 2 molecules of Glucose is oxidized into 2 molecules of pyruvatepyruvate

- the oxidizing agent is NAD+- the oxidizing agent is NAD+

- 2 ATP are made - 2 ATP are made with or without with or without oxygen oxygen (whether conditions are (whether conditions are aerobic or aerobic or anaerobicanaerobic))

Fermentation is an Fermentation is an extension extension of glycolysis of glycolysis that can generate ATP by substrate-level that can generate ATP by substrate-level phosphorylation (as long as there is NAD+)phosphorylation (as long as there is NAD+)

Fermentation consists of glycolysis plus Fermentation consists of glycolysis plus reactions that can regenerate NAD+ reactions that can regenerate NAD+

- - the NAD+ can then be reused to the NAD+ can then be reused to oxidize sugar by glycolysis, oxidize sugar by glycolysis, producing 2 molecules of ATPproducing 2 molecules of ATP

2 common types of fermentation:2 common types of fermentation:

ALCOHOL FERMENTATIONALCOHOL FERMENTATION

LACTIC ACID FERMENTATIONLACTIC ACID FERMENTATION

ALCOHOL FERMENTATIONALCOHOL FERMENTATION

Pyruvate is converted to ethanol (ethyl Pyruvate is converted to ethanol (ethyl alcohol) in 2 steps:alcohol) in 2 steps:

1. Pyruvate is converted to the 2-carbon 1. Pyruvate is converted to the 2-carbon compound acetaldehyde and COcompound acetaldehyde and CO22 is is releasedreleased

2. Acetaldehyde is reduced by NADH to 2. Acetaldehyde is reduced by NADH to ethanolethanol

- - NAD+ is regenerated for use in NAD+ is regenerated for use in glycolysisglycolysis

Alcohol fermentation by yeast is used Alcohol fermentation by yeast is used in brewing and winemakingin brewing and winemaking

- many bacteria also carry out alcohol - many bacteria also carry out alcohol fermentationfermentation

LACTIC ACID LACTIC ACID FERMENTATIONFERMENTATION

Pyruvate is reduced directly by NADH Pyruvate is reduced directly by NADH to form lactateto form lactate

- - no COno CO22 is released is released

Lactic acid fermentation by some fungi Lactic acid fermentation by some fungi and bacteria is used in the dairy and bacteria is used in the dairy industryindustry

- buttermilk- buttermilk

- yogurt- yogurt

- some cheeses- some cheeses

Human muscle cells also make lactic Human muscle cells also make lactic acid when oxygen is lowacid when oxygen is low

- occurs in early stages of strenuous exercise, - occurs in early stages of strenuous exercise, when sugar oxidation for ATP production when sugar oxidation for ATP production outpaces the muscle’s supply of oxygen outpaces the muscle’s supply of oxygen from the bloodfrom the blood

- - cells will switch from aerobic cells will switch from aerobic respiration to fermentationrespiration to fermentation

- lactate that accumulates causes burning - lactate that accumulates causes burning

- is gradually carried away by blood to the - is gradually carried away by blood to the liverliver

- - lactate is converted back to pyruvate lactate is converted back to pyruvate by liver cellsby liver cells

COMPARE FERMENTATION COMPARE FERMENTATION AND RESPIRATION?AND RESPIRATION?

SIMILARITIES:SIMILARITIES:

- both use glycolysis to oxidize glucose - both use glycolysis to oxidize glucose and other organic fuels to pyruvate and other organic fuels to pyruvate (net production of 2 ATP)(net production of 2 ATP)

- - NAD+ is the oxidizing agent that NAD+ is the oxidizing agent that accepts electrons from food accepts electrons from food during glycolysisduring glycolysis

DIFFERENCESDIFFERENCES

- In fermentation, the final electron - In fermentation, the final electron acceptor is an organic molecule, such acceptor is an organic molecule, such as pyruvate or acetaldehydeas pyruvate or acetaldehyde

- In respiration, the final electron - In respiration, the final electron acceptor is oxygenacceptor is oxygen

- much more ATP is produced in - much more ATP is produced in respiration >> respiration >> up to 38 as up to 38 as compared to 2 in fermentationcompared to 2 in fermentation

Some organisms (like yeasts and Some organisms (like yeasts and bacteria) can make enough ATP to bacteria) can make enough ATP to survive by using either pathway; survive by using either pathway; they can switchthey can switch

- these organisms are called - these organisms are called FACULTATIVE ANAEROBESFACULTATIVE ANAEROBES

- our muscle cells behave like - our muscle cells behave like facultative anaerobesfacultative anaerobes

GLYCOLYSIS AND GLYCOLYSIS AND EVOLUTIONEVOLUTION

There is evidence that the first There is evidence that the first prokaryotes produced ATP by glycolysisprokaryotes produced ATP by glycolysis

- - oldest known fossils of bacteria oldest known fossils of bacteria date back before oxygen was date back before oxygen was present in Earth’s atmospherepresent in Earth’s atmosphere

- glycolysis is the most widespread - glycolysis is the most widespread pathway, so this suggests that is pathway, so this suggests that is evolved very early in the history of lifeevolved very early in the history of life

- since glycolysis takes place in the - since glycolysis takes place in the cytosol, it does not require any of the cytosol, it does not require any of the membrane bound organelles (in membrane bound organelles (in eukaryotes) which did not evolve eukaryotes) which did not evolve until lateruntil later

BEYOND GLUCOSE?BEYOND GLUCOSE?

Cellular respiration can use other food Cellular respiration can use other food molecules to make ATPmolecules to make ATP

CARBOHYDRATESCARBOHYDRATES

- - starch and glycogen are starch and glycogen are hydrolyzed to glucosehydrolyzed to glucose

PROTEINSPROTEINS

- must first be broken down into amino - must first be broken down into amino acidsacids

- many are used to build new proteins, but - many are used to build new proteins, but the rest are converted by enzymes to the rest are converted by enzymes to intermediates of glycolysis and the Krebs intermediates of glycolysis and the Krebs cyclecycle

FATSFATS

- glycerol is converted to an intermediate of - glycerol is converted to an intermediate of glycolysisglycolysis

- - BETA OXIDATION breaks fatty acids BETA OXIDATION breaks fatty acids down into fragments that enter the down into fragments that enter the Krebs cycleKrebs cycle