Cell Respiration Topic 3.7 Cell Respiration Topic 8.1 Cell Respiration

Cell Respiration Cell Respiration

Topic 3.7 Cell RespirationTopic 3.7 Cell Respiration

Topic 8.1 Cell RespirationTopic 8.1 Cell Respiration

Cell RespirationCell Respiration

Who does it?Who does it?– All living things (including plants!)All living things (including plants!)

What is it?What is it?– Carbohydrates and OCarbohydrates and O22 are used to make ATP are used to make ATP

(energy). CO(energy). CO22 and H and H220 are waste products.0 are waste products.

– The opposite of photosynthesis.The opposite of photosynthesis.– Involves three steps: glycolysis, kreb’s cycle, Involves three steps: glycolysis, kreb’s cycle,

and electron transport chain.and electron transport chain. Where does it occur?Where does it occur?

– The cytoplasm and the mitochondria of the cellThe cytoplasm and the mitochondria of the cell

MitochondriaMitochondria

Cell RespirationCell Respiration

CC66HH1212OO66 + 6O + 6O22 6CO 6CO22 + 6H + 6H220 + ATP0 + ATP Glucose+ oxygenGlucose+ oxygen carbon dioxide + carbon dioxide +

water + energywater + energy

Redox ReactionsRedox Reactions Redox-reactionRedox-reaction, or an oxidation-, or an oxidation-

reduction reaction, is the movement of reduction reaction, is the movement of electrons from one molecule to another. electrons from one molecule to another.

Because an electron transfer requires Because an electron transfer requires both a donor and acceptor, oxidation both a donor and acceptor, oxidation and reduction always go together.and reduction always go together.

Cellular respiration is an example of a Cellular respiration is an example of a redox-reactionredox-reaction– ““fall” of electrons, with energy released in fall” of electrons, with energy released in

small amounts that can be stored in ATPsmall amounts that can be stored in ATP

Redox ReactionsRedox Reactions

OxidationOxidation– The loss of electrons from one substanceThe loss of electrons from one substance– Glucose loses electrons (in H atoms) and Glucose loses electrons (in H atoms) and

becomes oxidizedbecomes oxidized ReductionReduction

– The addition of elections to another The addition of elections to another substancesubstance

– OO22 gains electrons (in H atoms) and gains electrons (in H atoms) and becomes reducedbecomes reduced

Cell Respiration occurs in three Cell Respiration occurs in three main stagesmain stages

1.1. GlycolysisGlycolysisOccurs in the cytoplasm; glucose is broken Occurs in the cytoplasm; glucose is broken down to two pyruvate molecules; provides down to two pyruvate molecules; provides energy for ETCenergy for ETC

2.2. The citric acid cycle (Kreb’s cycle)The citric acid cycle (Kreb’s cycle)Takes place in the matrix of the mitochondria; Takes place in the matrix of the mitochondria; further breaks down pyruvate to carbon further breaks down pyruvate to carbon dioxide; provides energy for ETCdioxide; provides energy for ETC

3.3. Oxidative phosphorylation (Electron Oxidative phosphorylation (Electron Transport Chain)Transport Chain)

Takes place in the cristae of the mitochondria. Takes place in the cristae of the mitochondria. Also known as chemiosmosis; NADH and Also known as chemiosmosis; NADH and FADH2 made in glycolysis and Kreb’s shuttle FADH2 made in glycolysis and Kreb’s shuttle electrons and H+ to make ATP. electrons and H+ to make ATP.

GlycolysisGlycolysis Means “splitting sugar” Means “splitting sugar” Begins with a single molecule of glucose (6-C) Begins with a single molecule of glucose (6-C)

and concludes with two molecules of another and concludes with two molecules of another organic compound, called pyruvate (3-C).organic compound, called pyruvate (3-C).

A net gain of 2 NADH molecules and 2 ATP A net gain of 2 NADH molecules and 2 ATP moleculesmolecules

ATP can be used by cell immediately; NADH ATP can be used by cell immediately; NADH must pass down the ETC in mitochondriamust pass down the ETC in mitochondria

Substrate-level phophorylationSubstrate-level phophorylation occurs occurs– An enzyme transfers a phosphate group from a An enzyme transfers a phosphate group from a

substrate molecule directly to ADP, forming ATPsubstrate molecule directly to ADP, forming ATP

GlycolysisGlycolysis 9 Steps (Figure 6.7C)9 Steps (Figure 6.7C) Steps 1-3:Steps 1-3: A sequence of three chemical A sequence of three chemical

reactions converts glucose to a molecule reactions converts glucose to a molecule of fructose using 2 ATP. of fructose using 2 ATP.

Step 4:Step 4: Fructose splits into two G3P Fructose splits into two G3P moleculesmolecules

Step 5:Step 5: G3P gets oxidized and NAD+ is G3P gets oxidized and NAD+ is reduced to NADHreduced to NADH

Steps 6-9:Steps 6-9: specific enzymes make four specific enzymes make four molecules of ATP by substrate-level molecules of ATP by substrate-level phosphorylation. Water gets produced as a phosphorylation. Water gets produced as a by-productby-product

GlycolysisGlycolysis

2 ATP produced account only for 5% 2 ATP produced account only for 5% of the energy that a cell can harvest of the energy that a cell can harvest from a glucose molecule.from a glucose molecule.

2 NADH account for another 16%, 2 NADH account for another 16%, but there stored energy is not but there stored energy is not available for use in the absence of available for use in the absence of OO22. .

Pyruvate chemical Pyruvate chemical “grooming”“grooming”

As pyruvate forms at the end of As pyruvate forms at the end of glycolysis, it is transported from the glycolysis, it is transported from the cytoplasm into the mitochondria cytoplasm into the mitochondria

Pyruvate does not enter the Kreb’s Pyruvate does not enter the Kreb’s Cycle as itself. Cycle as itself.

It undergoes major chemical It undergoes major chemical “grooming”“grooming”

Pyruvate chemical Pyruvate chemical “grooming”“grooming” A large, multienzyme complex A large, multienzyme complex

catalyzes three reactions:catalyzes three reactions:1.1. A carbon atom is removed from pyruvate and A carbon atom is removed from pyruvate and

released in CO2released in CO2

2.2. The two-carbon compound remaining is The two-carbon compound remaining is oxidized while a molecule of NAD+ is reduced oxidized while a molecule of NAD+ is reduced to NADHto NADH

3.3. A compound called coenzyme A, derived from A compound called coenzyme A, derived from a B vitamin, joins with the two-carbon group to a B vitamin, joins with the two-carbon group to form a molecule called form a molecule called acetyl coenzyme Aacetyl coenzyme A::

Abbreviated acetyl CoA, is a high-energy fuel Abbreviated acetyl CoA, is a high-energy fuel molecule for the Kreb’s Cyclemolecule for the Kreb’s Cycle

For each molecule of glucose that enters glycolysis, For each molecule of glucose that enters glycolysis, two molecules of acetyl CoA are produced and enter two molecules of acetyl CoA are produced and enter the Kreb’s cycle.the Kreb’s cycle.

Pyruvate chemical Pyruvate chemical “grooming”“grooming”

Kreb’s CycleKreb’s Cycle Overview:Overview:

– Called Krebs in honor of Hans Krebs, German-Called Krebs in honor of Hans Krebs, German-British researcher who worked out much of this British researcher who worked out much of this cyclic phase of cellular respiration in the 1930s.cyclic phase of cellular respiration in the 1930s.

– Only the two-carbon acetyl part of the acetyl CoA Only the two-carbon acetyl part of the acetyl CoA molecule actually participates in the citric acid molecule actually participates in the citric acid cycle.cycle.

– Coenzyme A helps the acetyl group enter the cycle Coenzyme A helps the acetyl group enter the cycle and then splits off and is recycled. and then splits off and is recycled.

– Occurs in the matrix of the mitochondriaOccurs in the matrix of the mitochondria– Compared with glycolysis, Kreb’s Cycle pays big Compared with glycolysis, Kreb’s Cycle pays big

energy dividends to the cellenergy dividends to the cell– This makes 1 ATP, 4 NADH and 1 FADHThis makes 1 ATP, 4 NADH and 1 FADH22, per acetyl , per acetyl

coA (double that for each glucose molecule)coA (double that for each glucose molecule)– Releases COReleases CO22 as waste as waste – is aerobic (requires oxygen)is aerobic (requires oxygen)

Kreb’s CycleKreb’s Cycle Details of the citric acid cycle: Figure 6.9B:Details of the citric acid cycle: Figure 6.9B:

– Step 1Step 1 Acetyl coA Acetyl coA is stripped via enzymes: coA is recycle and is stripped via enzymes: coA is recycle and

the remaining acetyl (2-C) is combined with the remaining acetyl (2-C) is combined with oxaloacetateoxaloacetate already present in the mitochondria already present in the mitochondria forming forming citratecitrate (6-C) (6-C)

– Step 2 and 3Step 2 and 3 Redox reactions take place stripping hydrogen atoms Redox reactions take place stripping hydrogen atoms

from organic intermediates producing NADH molecules from organic intermediates producing NADH molecules and dispose of 2-C that came from oxaloacetate, which and dispose of 2-C that came from oxaloacetate, which are released as COare released as CO22..

Substrate-level phos. of ADP occurs to form ATP. Substrate-level phos. of ADP occurs to form ATP. A 4-C molecule called succinate forms. A 4-C molecule called succinate forms.

– Step 4 and 5Step 4 and 5 Oxaloacetate gets regenerated from maltate, and FAD Oxaloacetate gets regenerated from maltate, and FAD

and NADand NAD++ are reduced to FADH are reduced to FADH22 and NADH, and NADH, respectively.respectively.

Oxaloacetate is ready for another turn of the cycle by Oxaloacetate is ready for another turn of the cycle by accepting another acetyl groupaccepting another acetyl group

Kreb’s CycleKreb’s Cycle

Electron Transport ChainElectron Transport Chain

Involves oxidative phosphorylationInvolves oxidative phosphorylation– A clear illustration of structure fitting function: A clear illustration of structure fitting function:

the spatial arrangement of electron carriers the spatial arrangement of electron carriers built into a membrane makes it possible for the built into a membrane makes it possible for the mitochondrion to use the chemical energy mitochondrion to use the chemical energy released by redox reactions to create an H+ released by redox reactions to create an H+ gradient and then use the energy stored in the gradient and then use the energy stored in the gradient to drive ATP synthesisgradient to drive ATP synthesis

Chemiosmosis also occursChemiosmosis also occurs– The potential energy of the concentration The potential energy of the concentration

gradient is used to make ATP. gradient is used to make ATP.

Electron Transport ChainElectron Transport Chain

Built into the inner membrane of the Built into the inner membrane of the mitochondrion, or in the cristae folds, mitochondrion, or in the cristae folds, providing space for thousands of providing space for thousands of copies of the electron transport chain copies of the electron transport chain and many ATP synthase complexesand many ATP synthase complexes

With all these ATP-making With all these ATP-making “machines,” a mitochondrion can “machines,” a mitochondrion can produce many ATP molecules produce many ATP molecules simultaneously.simultaneously.

Electron Transport ChainElectron Transport Chain Figure 6.10:Figure 6.10:

– Path of electron flow from the shuttle Path of electron flow from the shuttle molecules NADH and FADHmolecules NADH and FADH22 to O to O22, the final , the final electron acceptor.electron acceptor.

– Each oxygen atom (1/2 OEach oxygen atom (1/2 O22) accepts two ) accepts two electrons from the chain and picks up two electrons from the chain and picks up two hydrogen ions from the surrounding hydrogen ions from the surrounding solution to form Hsolution to form H22O, one of the final O, one of the final products of cellular respiration. products of cellular respiration.

– Most of the carrier molecules reside in the Most of the carrier molecules reside in the three main protein complexes, while two three main protein complexes, while two mobile carriers transport electrons between mobile carriers transport electrons between the complexes.the complexes.

Electron Transport ChainElectron Transport Chain Figure 6.10 (continued):Figure 6.10 (continued):

– All of the carriers bind and release electrons All of the carriers bind and release electrons in redox reactions, passing electrons down in redox reactions, passing electrons down the “energy staircase.”the “energy staircase.”

– Protein complexes shown in the diagram use Protein complexes shown in the diagram use the energy released from the electron the energy released from the electron transfers to actively transport H+ across the transfers to actively transport H+ across the membrane, from where they are less membrane, from where they are less concentrated to where they are more concentrated to where they are more concentrated.concentrated.

– Hydrogen ions are transported from the Hydrogen ions are transported from the matrix of the mitochondrion (its innermost matrix of the mitochondrion (its innermost compartment) into the mitochondrion’s compartment) into the mitochondrion’s intermembrane space.intermembrane space.

Electron Transport Chain Figure 6.10 (continued):Figure 6.10 (continued):

– The resulting H+ gradient stores potential energy, similar to a dam storing energy by holding back elevated water. Dams can be harnessed to generate electricity when

the water is allowed to rush downhill, turning giant wheels called turbines.

Similarly, ATP synthases built into the inner mitochondrial membrane act like minature turbines. H+ can only cross through ATP synthases bc they are not permeable to the membrane.

Hydrogen ions rush back “downhill” through an ATP synthase, spinning a component of the complex, just as water turns the turbine in a dam.

Rotation activates catalytic sites in the synthase that attach phosphate groups to ADP molecules to generate ATP.

Electron Transport Chain

Why is this process called oxidative phosphorylation?– The energy derived from the oxidation-

reduction reactions of the electron transport chain that transfer electrons from organic molecules to oxygen is used to phosphorylate ADP.

– By chemosmosis, the exergonic reactions of electron transport produce an H+ gradient that drives the endergonic synthesis of ATP.

Cell Respiration Summary TOTAL= 38 ATP (theoretical) Glycolysis

– Occurs in cytoplasm– 2 ATP– 2 NADH– 2 H20 get released– 2 pyruvate

Kreb’s Cycle (including pyruvate grooming)– 2 ATP– 8 NADH– 2 FADH2– 6 CO2 get released

Electron Transport Chain– H20 gets released– 10 NADH get converted to 3ATP= 30 ATP– 2 FADH2 get converted to 2 ATP= 4 ATP

Poisons

Some poisons block the electron transport chain.

Rotenone – Often used to kill pest insects and fish.– binds tightly with the electron carrier

molecules in the first protein complex, preventing electrons from passing to the next carrier molecule.

– Literally starves an organism’s cells of energy bc it blocks the ETC near its start thus preventing ATP synthesis.

Poisons

Cyanide and Carbon Monoxide– Bind with an electron carrier in the third

protein complex– Block the passage of electrons to oxygen– Similar to turning off a faucet; electrons

cease to flow through the “pipe” – Result is the same as that or rotenone: no

H+ gradient is generate and no ATP is made.

***refer to page 99 in your book for other examples***

Fermentation-Anaerobic Respiration

Glycolysis is the metabolic pathway that generates ATP during fermentation.

No O2 is required; it generates a net gain of 2 ATP while oxidizing glucose to two molecules of pyruvate and reducing NAD+ to NADH.

Significantly less ATP is generated, but it is enough to keep your muscles contracting for a short while when the need for ATP outpaces the delivery of O2 via the blood stream

Many microorganisms supply all their energy needs with the 2 ATP yield of glycolysis.


Strict AnaerobesStrict Anaerobes

require anaerobic conditions and are require anaerobic conditions and are poisoned by oxygenpoisoned by oxygen

Facultative AnaerobesFacultative Anaerobes

can make ATP either by fermentation can make ATP either by fermentation or by oxidative phosphorylation, or by oxidative phosphorylation, depending on whether O2 is depending on whether O2 is available. available.


Fermentation provides an anaerobic Fermentation provides an anaerobic step that recycles NADH back to step that recycles NADH back to NAD+; essential to harvest food NAD+; essential to harvest food energy by glycolysis.energy by glycolysis.

Two types of fermentation:Two types of fermentation:– Lactic acidLactic acid– AlcoholAlcohol


Lactic acid fermentationLactic acid fermentation– Figure 6.13AFigure 6.13A– NADH is oxidized to NAD+ as pyruvate NADH is oxidized to NAD+ as pyruvate

is reduced to lactate (the ionized form is reduced to lactate (the ionized form of lactic acid)of lactic acid)

– Lactate builds up in muscle cells during Lactate builds up in muscle cells during strenuous exercise is carried in the strenuous exercise is carried in the blood to the liver, where it is converted blood to the liver, where it is converted back to pyruvateback to pyruvate

– Dairy industry use this to with bacteria Dairy industry use this to with bacteria to make cheese and yogurtto make cheese and yogurt


Alcohol fermentationAlcohol fermentation– Figure 6.13AFigure 6.13A– Used in brewing, winemaking, and bakingUsed in brewing, winemaking, and baking– Used by yeasts and bacteria (facultative Used by yeasts and bacteria (facultative

anaerobes)anaerobes)– Recycle their NADH to NAD+ while converting Recycle their NADH to NAD+ while converting

pyruvate to CO2 and ethanol (ethyl alcohol).pyruvate to CO2 and ethanol (ethyl alcohol).– CO2 provides bubbles in beer and champagne, CO2 provides bubbles in beer and champagne,

and bread dough to riseand bread dough to rise– Ethanol is toxic to organisms that produce it; Ethanol is toxic to organisms that produce it;

must release it to their surroundingsmust release it to their surroundings

Fuels for cell respirationFuels for cell respiration

Free glucose molecules are not Free glucose molecules are not common in our dietcommon in our diet

We obtain most of our calories as We obtain most of our calories as fats, proteins, sucrose, and other fats, proteins, sucrose, and other disaccharide sugars, and starchdisaccharide sugars, and starch


Carbohydrates (polysaccharides and Carbohydrates (polysaccharides and starch)starch)– Figure 6.14Figure 6.14– Enzymes in our digestive tract hydrolyze Enzymes in our digestive tract hydrolyze

starch to glucose; glycogen can be starch to glucose; glycogen can be hydrolyzed to glucose to serve as fuel hydrolyzed to glucose to serve as fuel between meals.between meals.


Proteins:Proteins:– First must be digested to their constituent First must be digested to their constituent

amino acidsamino acids– Typically, cell will use most of the amino Typically, cell will use most of the amino

acids to make its own proteins, but acids to make its own proteins, but enzymes will convert excess a.a. to enzymes will convert excess a.a. to intermediates of glycolysis or the Kreb’s intermediates of glycolysis or the Kreb’s cycle, and their energy is harvested by cell cycle, and their energy is harvested by cell respiration. respiration.

– Amino groups unused are disposed in urine.Amino groups unused are disposed in urine.

Fuels for cell respirationFuels for cell respiration Fats:Fats:

– Excellent cellular fuel bc they contain many Excellent cellular fuel bc they contain many hydrogen atoms and thus many energy-rich hydrogen atoms and thus many energy-rich electrons electrons

– Cell first hydrolyzes fats to glycerol and fatty Cell first hydrolyzes fats to glycerol and fatty acidsacids

– It converts glycerol to G3P; fatty acids are It converts glycerol to G3P; fatty acids are broken into 2-carbon fragments that enter the broken into 2-carbon fragments that enter the Kreb’s as acetyl coAKreb’s as acetyl coA

– A gram of fat yields more than twice as much A gram of fat yields more than twice as much ATP as a gram of starch.ATP as a gram of starch.

– Because so many calories are in each gram of Because so many calories are in each gram of fat, a person must expend a large amount of fat, a person must expend a large amount of energy to burn fat stored in the body.energy to burn fat stored in the body.


Food is also used as the raw Food is also used as the raw materials a cell uses for biosyntheis, materials a cell uses for biosyntheis, to make its own molecules for repair to make its own molecules for repair and growth…not just for ATP!and growth…not just for ATP!

To make cells, tissues, and To make cells, tissues, and organisms:organisms:– Amino acidsAmino acids proteins proteins– Fatty acids and glycerolsFatty acids and glycerols fats fats– SugarsSugars carbohydrates carbohydrates

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Cell Respiration Topic 3.7 Cell Respiration Topic 8.1 Cell Respiration