Essential Idea Energy is converted to a usable form in cell respiration

Essential Idea

• Energy is converted to a usable form in cell respiration.

Understandings• Cell respiration involves the oxidation and reduction of electron

carriers.

• Phosphorylation of molecules makes them less stable.

• In glycolysis, glucose is converted to pyruvate in the cytoplasm.

• Glycolysis gives a small net gain of ATP without the use of oxygen.

• In aerobic cell respiration pyruvate is decarboxylated and oxidized, and converted into acetyl compound and attached to coenzyme A to form acetyl coenzyme A in the link reaction.

• In the Krebs cycle, the oxidation of acetyl groups is coupled to the reduction of hydrogen carriers, liberating carbon dioxide.

• Energy released by oxidation reactions is carried to the cristae of the mitochondria by reduced NAD and FAD.

• Transfer of electrons between carriers in the electron transport chain in the membrane of the cristae is coupled to proton pumping.

Compare Oxidation vs. Reduction

Oxidation

• Lose electron

• Gain Oxygen

• Lose hydrogen

• Lose energy

• ATP is oxidized to ADP + P

• NADH is oxidized to NAD +H

Reduction

• Gain electron

• Lose oxygen

• Gain hydrogen

• Gain energy

• ADP is reduced to ATP

• NAD is reduced to NADH

IB Assessment Statement

• State that oxidation involves the loss of electrons from an element, and that oxidation frequently involves gaining oxygen or losing hydrogen,

• State that reduction involves a gain of electrons; reduction frequently involves losing oxygen or gaining hydrogen.

Oxidation

• Oxidation: often associated with the release of energy

Reduction

• Reduction: often associated with the gain of energy

Forms of Oxidation & Reduction

• In respiration the oxidation of organic compounds is coupled to the reduction of ADP to ATP.

• The oxidation of ATP is then coupled to biological processes such as muscle contraction of protein synthesis.

Ib Assessment Statement

• Outline the process of glycolysis, including phosphorylation, lysis, oxidation and ATP formation. 2 In the cytoplasm, one hexose sugar is converted into two three-carbon atom compounds (pyruvate) with a net gain of two ATP and two NADH + H+.

The Stages of Cellular Respiration: A Preview

• Cellular respiration has three stages:

1. Glycolysis (breaks down glucose into two molecules of pyruvate)

2. The citric acid cycle/ Krebs Cycle (completes the breakdown of glucose)

3. Oxidative phosphorylation (accounts for most of the ATP synthesis)

• The latter process generates most of the ATP is called oxidative phosphorylation because it is powered by redox reactions

Products of Glycolysis

• For every one molecule of glucose:

– 2 molecules of pyruvate are produced

– 2 ATP are produced

– 2 NAD+ are converted to NADH + H

Four Steps of Glycolysis

1. Phosphorylation

2. Lysis(splitting)

3. Oxidation

4. ATP formation

Glycolysis harvests energy by oxidizing glucose to pyruvate

• Glycolysis (“splitting of sugar”) breaks down glucose into two molecules of pyruvate

• Glycolysis occurs in the cytoplasm

• Requires NO oxygen and so is considered an Anaerobic Reaction

• The overall reaction for glycolysis is for every one molecule of glucose used:

– 2 molecules of Pyruvate are formed

– 2 net molecules of ATP are formed

– 2 molecules of NADH are formed

Understand Glycolysis:

• Glycolysis Animations

• http://tinyurl.com/yayelo9

• http://programs.northlandcollege.edu/biology/Biology1111/animations/glycolysis.html

• http://www.iubmb-nicholson.org/swf/glycolysis.swf

There are four steps to the process of glycolysis

1. Phosphorylation

2. Lysis(splitting)

3. Oxidation

4. ATP formation

Steps of Glycolysis:

1. Phosphorylation – a reaction that uses 2 molecules of ATP molecules, and has three steps. First a phosphate group is added to glucose producing glucose phosphate.

– Phosphorylation of molecules makes them less stable.

Steps of Phosphorylation:

Second glucose phosphate is change to fructose phosphate

Steps of Phosphorylation:

Third another phosphate is added from ATP to fructose phosphate and changed to fructose diphosphate.

Steps of Glycolysis

Step 2 in glycolysis: Lysis (splitting)

The glucose molecule is split into two 3-carbon molecules called triose phosphate

Steps of Glycolysis

Step 3 in glycolysis: Oxidation of triose phosphate molecule. Removes a hydrogen and attaches the hydrogen to Nicotinamide adenine dinucleotide, NAD+ producing NADH and 2 new molecules called triose phosphate.

Steps of Glycolysis

Step 4 ATP Formation –

– Two triose phosphate molecules are converted to 2 pyruvate molecules

– Four ATP molecules are formed.

Net ATP gain in Glycolysis

• For every on molecule of Glucose used in glycolysis

– 2 molecules of ATP are use

– 4 molecules of ATP are formed

2 molecules of net ATP are made

Total Products of glycolysis

• For every one molecule of glucose:

– 2 molecules of pyruvate are produced

– 2 ATP are produced

– 2 NAD+ are converted to NADH + H

LE 9-8

Energy investment phase

Glucose

2 ATP used2 ADP + 2 P

4 ADP + 4 P 4 ATP formed

2 NAD+ + 4 e– + 4 H+

Energy payoff phase

+ 2 H+2 NADH

2 Pyruvate + 2 H2O

2 Pyruvate + 2 H2O

2 ATP

2 NADH + 2 H+

Glucose

4 ATP formed – 2 ATP used

2 NAD+ + 4 e– + 4 H+

Net

Glycolysis Citricacidcycle

Oxidativephosphorylation

ATPATPATP

Draw an annotated diagram of the process of glycolysis

Be sure to include/ label:

– 6 carbon sugar (glucose)

– Phosphorylation (adding 2 phosphates by via oxidation of ATP)

– Lysis – splitting the 6 Carbon sugar to 3 carbon sugars

– Add more phosphate to triose sugar

– Reduction of NAD+

– 4 ATP formation via reduction of ADP

– 2 three carbon pyruvate molecules

IB Assessment Statement

• Draw and label a diagram showing the structure of a mitochondrion as seen in electron micrographs.

Krebs Cycle

Step 2 in cellular repiration: the Krebs cycle.

– The Krebs Cycle – Occurs in the mitochondria of cells

mitochondrion

animal cell

Structure of the mitochondria.

• Location of aerobic respiration

• Pyruvate, the product of glycolysis can be further oxidised here to release more energy.

• Mitochondria are only found in eukaryotic cells.

• Cells that need a lot of energy will have many mitochondria ( liver cell) or can develop them under training (muscles cells).

Structure of the mitochondria.

• There is a double membrane.

• The inner membrane is folded to form 'cristae'.

• There is a space between the two membranes which is important for creating a place to concentrate H+

• The inner space is called the matrix.

• Mitochondria contain some of their own DNA (mDNA).

IB Assessment Statement

• Explain aerobic respiration, including the link reaction, the Krebs cycle, the role of NADH + H+, the electron transport chain and the role of oxygen.

Stages in the Aerobic respiration:

• Link Reaction: Pyruvate is transported into the matrix of the mitochondria and is decarboxylated (loses CO2)

• Krebs cycle: carbon fragments (C2) are progressively decarboxylated to yield ATP and reduced coenzymes

• Electron Transport System: reduced coenzymes are used to generate more ATP (see 8.1.5).

Link Cycle to Krebs cycle

• The pyruvate from glycolysis diffuses into the matrix of the mitochondria.

• Before the Krebs cycle can begin, pyruvate must be converted to acetyl CoA, which links the cycle to glycolysis (LINK REACTION)

• Krebs cycle requires oxygen. So is considered an aerobic reaction.

LE 9-6_1

Mitochondrion

Glycolysis

PyruvateGlucose

Cytosol

ATP

Substrate-levelphosphorylation

LE 9-6_2

Mitochondrion

Glycolysis

PyruvateGlucose

Cytoplasm

ATP

Substrate-levelphosphorylation

ATP

Substrate-levelphosphorylation

Krebscycle

Link Reaction

CYTOPLASM

Pyruvate

NAD+

MITOCHONDRION

Transport protein

NADH + H+

Coenzyme ACO2

Acetyl Co A

Link Reaction: Pyruvate(3C) is transported to the matrix of the mitochondria

• A large Co-enzyme A joins with the 3 carbon fragment pyruvate.

• Pyruvate is decarboxylated removing a single carbon as carbon dioxide.

• The remaining carbon fragment is an Acetyl group and temporarily forms Acetyl CoA.

• NAD+ is reduced to NADH + H+.

• Acetyl (2C) is already transported into the matrix of mitochondria

Krebs Cycle Overview

•The Krebs cycle, takes place within the mitochondrial matrix

•The cycle oxidizes organic fuel derived from pyruvate, generating one ATP, 3 NADH, and 1 FADH2 per turn

Pyruvate(from glycolysis,2 molecules per glucose)

ATP ATP ATP

Glycolysis Oxidationphosphorylation

Citricacidcycle

NAD+

NADH

+ H+

CO2

CoA

Acetyl CoA

CoA

CoA

Calvincycle

CO22

3 NAD+

+ 3 H+

NADH3

ATP

ADP + P i

FADH2

FAD

Pyruvate(from glycolysis,2 molecules per glucose)

ATP ATP ATP

Glycolysis Oxidationphosphorylation

CitricacidcycleNAD+

NADH

+ H+

CO2

CoA

Acetyl CoACoA

CoA

Calvincycle CO2

2

3 NAD+

+ 3 H+

NADH3

ATP

ADP + P i

FADH2

FAD

Krebs Cycle Overview

•The krebs cycle has many steps, each catalyzed by a specific enzyme

•The acetyl group of acetyl CoA joins the cycle by combining with oxaloacetate, forming citrate

•The next several steps decompose the citrate back to oxaloacetate, making the process a cycle

•The NADH and FADH2 produced by the cycle relay electrons extracted from food to the electron transport chain

ATP ATP ATP

Glycolysis Oxidationphosphorylation

Citricacidcycle

Calvincycle

CitrateIsocitrate

Oxaloacetate

Acetyl CoA

H2O

CO2

NAD+

NADH+ H+

-Ketoglutarate

CO2NAD+

NADH+ H+Succinyl

CoA

Succinate

GTPGDP

ADP

ATP

FAD

FADH2

Pi

Fumarate

H2O

Malate

NAD+

NADH+ H+

Krebs Cycle: oxidative decarboxylation of the C2 Acetyl group (CH3CO). This cycle has been broken down into 4 steps. The carbons from the original glucose molecule are shown in purple and those of mitochondria molecules in blue

Step 1

•Acetyl CoA joins with the C4(acceptor)group (Oxaloacetate)

•CoA is released to transport more pyruvate into the matrix

•A C6 fragment is formed (citric acid)

ATP ATP ATP

Glycolysis Oxidationphosphorylation

Citricacidcycle

Krebscycle

Citrate

Isocitrate

Oxaloacetate

Acetyl CoA

H2O

Step 1

Acetyl CoA joins with the C4(acceptor)group (oxaloacetate)

CoA is released to transport more pyruvate into the matrix

A C6 fragment is formed (citric acid)

Krebs Cycle: oxidative decarboxylation of the C2 Acetyl group (CH3CO). This cycle has been broken down into 4 steps. The carbons from the original glucose molecule are shown in purple and those of mitochondria molecules in blue

Step 2

•C6 (Citric Acid) is oxidatively decarboxylated.

•A C5 group is formed.

•The Carbon is given off as Carbon Dioxide

•NAD+ is reduced to NADH + H+

LE 9-12_2

ATP ATP ATP

Glycolysis Oxidationphosphorylation

Citricacidcycle

Citricacidcycle

Citrate

Isocitrate

Oxaloacetate

Acetyl CoA

H2O

CO2

NAD+

NADH

+ H+

-Ketoglutarate

CO2NAD+

NADH

+ H+SuccinylCoA

Step 2

C6 (Citric Acid) is oxidatively decarboxylated.

A C5 group is formed.

The Carbon is given off as Carbon Dioxide

NAD+ is reduced to

NADH + H+

Krebs Cycle: oxidative decarboxylation of the C2 Acetyl group (CH3CO). This cycle has been broken down into 4 steps. The carbons from the original glucose molecule are shown in purple and those of mitochondria molecules in blue

Step 3

•The C5 fragment is oxidised and decarboxylated further to a C4 compound (-Ketoglutarate)

•Again the carbon removed forms carbon dioxide.

•NAD+ is further reduced to NADH + H+.

Krebs Cycle: oxidative decarboxylation of the C2 Acetyl group (CH3CO). This cycle has been broken down into 4 steps. The carbons from the original glucose molecule are shown in purple and those of mitochondria molecules in blue

Step 4

•The final stage in the cycle has the C4 acceptor regenerated.

•There is a reduction of NAD+ to NADH + H+.

•FAD (Coenzyme)is reduced to FADH2 .

•ADP is reduced to ATP

LE 9-12_4

ATP ATP ATP

Glycolysis Oxidationphosphorylation

Citricacidcycle

Calvincycle

Citrate

Isocitrate

Oxaloacetate

Acetyl CoA

H2O

CO2

NAD+

NADH

+ H+

-Ketoglutarate

CO2NAD+

NADH

+ H+SuccinylCoA

Succinate

GTP GDP

ADP

ATP

FAD

FADH2

P i

Fumarate

H2O

Malate

NAD+

NADH

+ H+

Step 4

The final stage in the cycle has the C4 acceptor (oxaloacetate) regenerated.

There is a reduction of NAD+ to NADH + H+.

FAD (Coenzyme)is reduced to FADH2 .

ADP is reduced to ATP

Summarizing the Krebs Cycle for every one pyruvate molecule

• Two molecules of carbon dioxide are given off

• One molecule of ATP is formed

• Three molecules of NADH are formed

• One molecule of flavin adenine dinucleotide FADH are formed

• FADH and NADH carries electrons to the next step in respiration, the electron transport chain.

Krebs Cycle Summary

• (a) Pyruvate (3C)

• (b) Link reaction

• (c) C4 + C2= C6

• (d) Recycling of CoA

• (e) Decarboxylation C6 to C5 and the reduction of NAD

• (f) Decarboxylation C5 to C4 and the reduction of NAD

• (g) C4 to C4 with the reduction of coenzymes FAD and NAD. ATP is made directly.

• (h) C4 to C4 acceptor

• This cycle follows one acetyl group.

• Each glucose that enters glycolysis will produce 2 acetyl groups.

Krebs Cycle Animations

• http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::525::530::/sites/dl/free/0072464631/291136/krebsCycle.swf::krebsCycle.swf

• http://www.wiley.com/legacy/college/boyer/0470003790/animations/tca/tca.htm

• http://www.wiley.com/college/pratt/0471393878/student/animations/citric_acid_cycle/index.html

Krebs Cycle Resources & Help

• http://www2.nl.edu/jste/aerobic_respiration.htm

• http://www.wiley.com/college/pratt/0471393878/student/animations/citric_acid_cycle/index.html

Draw the Link Reaction & the Krebs Cycle

• Be sure to Label the C4 Molecule (oxaloacetate) in the beginning of the cycle and the end of the cycle

• Show one decarboxylation (loss of CO2) in the link reaction and the resulting 2 carbon molecule & reduction of NAD

• Show two decarboxylation (loss of CO2) in the kreb cycle reaction and show the resulting 5 and 4 carbon molecules

• Show the three reduction of NAD to NADH

• Show the one Reduction of FAD to FADH2

• Show the reduction of ADP to ATP

LE 9-6_3

Mitochondrion

Glycolysis

PyruvateGlucose

Cytosol

ATP

Substrate-levelphosphorylation

ATP

Substrate-levelphosphorylation

Citricacidcycle

ATP

Oxidativephosphorylation

Oxidativephosphorylation:electron transport

andchemiosmosis

Electronscarried

via NADH

Electrons carriedvia NADH and

FADH2

IB Assessment Statement

• Explain oxidative phosphorylation in terms of chemiosmosis.

During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis

• Following glycolysis and the kreb cycle, NADH and FADH account for most of the energy extracted from food

• These two electron carriers donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation

NADH

50

FADH2

40 FMN

Fe•S

I FAD

Fe•S II

IIIQ

Fe•S

Cyt b

30

20

Cyt c

Cyt c1

Cyt a

Cyt a3

IV

10

0

Multiproteincomplexes

Fre

e en

erg

y (G

) re

lati

ve t

o O

2 (k

cal/m

ol)

H2O

O22 H+ + 1/2

Carrier Protiens

The electron transport chain is in the cristae (folds in the inner membrane of the mitochondrion)

Electron transport chain consist of proteins proteins called carriers imbedded in called carriers imbedded in the cristae.the cristae.

The carrier proteins alternate in accepting (being reduce) and donating (being oxidized) electrons

Electrons drop in energy as they go down the chain and are finally passed to O2, forming water

Oxidative Phosphorylation coupled to the synthesis of ATP.

•Electron transfer in the electron transport chain causes proteins to pump H+ from the mitochondrial matrix to the intermembrane space

•The NADH is oxidized and the reduced proteins transport H+ from the matrix into the space between both mitochondrial membranes.

•There is electron transfer down the chain of proteins in a series of oxidation and reductions.

•For each NADH, 3 Moles of H+ are pumped into the space.

Oxidative Phosphorylation coupled to the synthesis of ATP.

•The FADH2is oxidized and the reduced membrane proteins pump H+into the space between the mitochondrial membranes.

•One FADH2 produces two moles of hydrogen ions.

A concentration gradient has been created between the high concentration of H+ between the mitochondrial membranes and the lower concentration in the matrix.

• ATP synthetase is an enzyme embedded in the cristae membrane.

• H+create an electrochemical gradient (chemical potential energy).C

• The H+ pass through a channel in the enzyme driving the motor.

• The motor spins bringing together ADP and Pi to produce ATP

At the end of the Electron Transport Chain the electrons are given to oxygen. At the same time oxygen accepts hydrogen to form water.

Summary of Electron Transport Chain & Chemiosmosis

INTERMEMBRANE SPACE

H+ H+

H+H+

H+

H+

H+

H+

ATP

MITOCHONDRAL MATRIX

ADP+

Pi

A rotor within the membrane spins as shown when H+ flows past it down the H+ gradient.

A stator anchored in the membrane holds the knob stationary.

A rod (or “stalk”) extending into the knob also spins, activating catalytic sites in the knob.

Three catalytic sites in the stationary knob join inorganic phosphate to ADP to make ATP.

Summary of Chemiosmosis• Movement of

Hydrogen ions with its concentration gradient.

• These movement across the membrane protein ATP synthase provides energy needed to generate ATP.

LE 9-15

Protein complexof electroncarriers

H+

ATP ATP ATP

GlycolysisOxidative

phosphorylation:electron transportand chemiosmosis

Citricacidcycle

H+

Q

IIII

II

FADFADH2

+ H+NADH NAD+

(carrying electronsfrom food)

Innermitochondrialmembrane

Innermitochondrialmembrane

Mitochondrialmatrix

Intermembranespace

H+

H+

Cyt c

IV

2H+ + 1/2 O2 H2O

ADP +

H+

ATP

ATPsynthase

Electron transport chainElectron transport and pumping of protons (H+),

Which create an H+ gradient across the membrane

P i

ChemiosmosisATP synthesis powered by the flow

of H+ back across the membrane

Oxidative phosphorylation

Summary of Electron Transport Chain & ChemiosmosisSummary of Electron Transport Chain & Chemiosmosis

An Accounting of ATP Production by Cellular Respiration

• During cellular respiration, most energy flows in this sequence:

glucose NADH electron transport chain proton-motive force ATP

• About 40% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 38 ATP

Electron Transport & Chemiosmosis Animation

• http://www.stolaf.edu/people/giannini/flashanimat/metabolism/mido%20e%20transport.swf

• http://www.iubmb-nicholson.org/swf/ATPSynthase.swf

• http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120071/bio11.swf::Electron%20Transport%20System%20and%20ATP%20Synthesis

• http://www.stolaf.edu/people/giannini/flashanimat/metabolism/atpsyn2.swf

• http://www.chem.purdue.edu/courses/chm333/oxidative_phosphorylation.swf

LE 9-16

CYTOSOL Electron shuttlesspan membrane 2 NADH

or

2 FADH2

MITOCHONDRION

Oxidativephosphorylation:electron transport

andchemiosmosis

2 FADH22 NADH 6 NADH

Citricacidcycle

2AcetylCoA

2 NADH

Glycolysis

Glucose2

Pyruvate

+ 2 ATP

by substrate-levelphosphorylation

+ 2 ATP

by substrate-levelphosphorylation

+ about 32 or 34 ATP

by oxidation phosphorylation, dependingon which shuttle transports electronsform NADH in cytosol

About36 or 38 ATPMaximum per glucose:

LE 9-18

Pyruvate

Glucose

CYTOSOL

No O2 presentFermentation

Ethanolor

lactate

Acetyl CoA

MITOCHONDRION

O2 present Cellular respiration

Citricacidcycle

LE 9-19

Citricacidcycle

Oxidativephosphorylation

Proteins

NH3

Aminoacids

Sugars

Carbohydrates

Glycolysis

Glucose

Glyceraldehyde-3- P

Pyruvate

Acetyl CoA

Fattyacids

Glycerol

Fats

• Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration

• A small amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation

IB Assessment Statement

• Explain the relationship between the structure of the mitochondrion and its function.

Structure and function of the mitochondria.

8.1.6 Relationship between the structure and function of the mitochondria.

•1. Cristae folds increase the surface area for electron transfer system.

•2. The double membrane creates a small space into which the H+ can be concentrated.

•3. Matrix creates an isolated space in which the krebs cycle can occur.

Nature of Science

• Paradigm shift—the chemiosmotic theory led to a paradigm shift in the field of bioenergetics. (2.3)

Skills and Application

• Application: Electron tomography used to produce images of active mitochondria.

• Skill: Analysis of diagrams of the pathways of aerobic respiration to deduce where decarboxylation and oxidation reactions occur.

• Skill: Annotation of a diagram of a mitochondrion to indicate the adaptations to its function..