Chapter 8 ppt

(1)

Biology

Sylvia S. Mader Michael Windelspecht

Chapter 8 Cellular

Respiration

Lecture Outline

See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into

PowerPoint without notes.

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Outline

• 8.1 Cellular Respiration

• 8.2 Outside the Mitochondria:

Glycolysis

• 8.3 Outside the Mitochondria

• 8.4 Inside the Mitochondria

• 8.5 Metabolic Pool

(3)

8.1 Cellular Respiration

• Cellular respiration is a cellular process that breaks

down nutrient molecules with the concomitant production of ATP

• Consumes oxygen and produces carbon dioxide (CO₂)

 Cellular respiration is an aerobic process.

• Usually involves the breakdown of glucose to CO₂ and

H₂O

 Energy is extracted from the glucose molecule:

• Released step-wise

• Allows ATP to be produced efficiently

 Oxidation-reduction enzymes include NAD+_{and FAD as}

(4)

Cellular Respiration

4



Electrons are removed from substrates and

received by oxygen, which combines with

H

+

to become water.



Glucose is oxidized and O

₂

is reduced

energy

glucose

Reduction Oxidation

6H₂O

6CO₂

6O₂

(5)

Cellular Respiration

5

O₂and glucose enter cells,

which release H₂O and CO.

CO2

H2O

Mitochondria use energy from

glucose to form ATP from ADP + P .

ATP ADP + P

cristae

intermembrane space

(6)

Cellular Respiration

NAD

+

(nicotinamide adenine dinucleotide)

 A coenzyme of oxidation-reduction. It can:

• Oxidize a metabolite by accepting electrons • Reduce a metabolite by giving up electrons

 Each NAD+_{molecule is used over and over again}

• FAD

(flavin adenine dinucleotide)

 Also a coenzyme of oxidation-reduction

 Sometimes used instead of NAD+

 Accepts two electrons and two hydrogen ions (H+_{) to}

become FADH₂

(7)

Cellular Respiration

• Cellular respiration includes four phases:



Glycolysis

is the breakdown of glucose into

two molecules of pyruvate

• Occurs in the cytoplasm • ATP is formed

• Does not utilize oxygen



Preparatory (prep)

reaction

• Both pyruvates are oxidized and enter the mitochondria

• Electron energy is stored in NADH

• Two carbons are released as CO₂(one from each

pyruvate)

(8)

Cellular Respiration



Citric acid cycle

• Occurs in the matrix of the mitochondrion and

produces NADH and FADH₂

• In series of reactions, it releases 4 carbons as CO₂

• Turns twice per glucose molecule (once for each pyruvate)

• Produces two immediate ATP molecules per glucose molecule



Electron transport chain (ETC)

• Extracts energy from NADH & FADH₂

• Passes electrons from higher to lower energy states

• Produces 32 or 34 molecules of ATP

(9)

The Four Phases of Complete

Glucose Breakdown

9

Electron transport chain and chemiosmosis

Mitochondrion

4 ADP 2

4 ATP total net gain 2 ATP

Glycolysis

NADH

glucose pyruvate Cytoplasm

ATP

e–

e– e

–

e–

(10)

The Four Phases of Complete

Glucose Breakdown

10

Preparatory reaction NADH

NADH and

FADH2

Electron transport chain and chemiosmosis

Mitochondrion

2

4 ATP total

net gain 2 ATP

Glycolysis

NADH

glucose pyruvate

Cytoplasm

ATP

e–

2 ATP

e–

4 ADP

(11)

The Four Phases of Complete

Glucose Breakdown

11

Mitochondrion

Citric acid cycle Preparatory reaction

2 ADP 2 NADH

Glycolysis

NADH

Cytoplasm

ATP 2

4 ATP total

net gain 2 ATP

ATP 2 ATP

4 ADP

Electron transport chain and chemiosmosis NADH and

FADH₂

e–

(12)

The Four Phases of Complete

Glucose Breakdown

12

Mitochondrion

Preparatory reaction

2 32 ADP

or 34 32 or 34 NADH Glycolysis NADH

Cytoplasm ATP e– e– e– e– e– e– e– Citric acid cycle Electron transport chain and chemiosmosis NADH and FADH2 2

4 ATP total

net gain 2 ATP ATP 2 ATP 4 ADP ATP 2 ADP

(13)

8.2 Outside the Mitochondria:

Glycolysis

• Glycolysis occurs in cytoplasm outside mitochondria

• Energy Investment Step:

 Two ATP are used to activate glucose

 Glucose splits into two G3P molecules

• Energy Harvesting Step:

 Oxidation of G3P occurs by removal of electrons and hydrogen

ions

 Two electrons and one hydrogen ion are accepted by NAD+

resulting in two NADH

 Four ATP are produced by substrate-level phosphorylation

 Net gain of two ATP (4 ATP produced - 2 ATP consumed)

 Both G3Ps converted to pyruvates

(14)

Outside the Mitochondria:

Glycolysis

14

2

4 Glycolysis

inputs

6C glucose

2 NAD

+

ATP

4 ADP + 4 P

ATP

net gain

total

ATP

2 ADP

2 NADH

pyruvate

outputs

(15)

Glycolysis

G3P glyceraldehyde-3-phosphate

BPG 1,3-bisphosphoglycerate

3PG 3-phosphoglycerate Energy-investment Step

(16)

Glycolysis

3PG 3-phosphoglycerate

ADP ADP

ATP ATP

glucose Glycolysis

(17)

Glycolysis

Two ATP are used to get started.

ADP ADP

–2 ATP

Energy-investment Step

ATP ATP

(18)

Glycolysis

G3P glyceraldehyde-3-phosphate BPG 1,3-bisphosphoglycerate 3PG 3-phosphoglycerate

Splitting produces two 3-carbon molecules.

G3P G3P

ADP ADP

–2 ATP

ATP ATP glucose

(19)

Glycolysis

Oxidation of G3P occurs as NAD+_{receives high-energy}

electrons. Energy-harvesting Steps

NADH NADH

BPG BPG G3P G3P

NAD+

ADP ADP

–2 ATP

ATP ATP glucose

Glycolysis

(20)

Glycolysis

A D P

electrons.

Substrate-level ATP synthesis.

+2 ATP ATP

3PG Energy-harvesting Steps

NADH NADH

ATP

BPG BPG

ADP G3P

G3P

NAD+

ADP ADP

–2 ATP

ATP ATP

glucose Glycolysis

3PG E2

(21)

Glycolysis

A D P

electrons.

Oxidation of 3PG occurs by removal of water.

+2 ATP ATP

3PG

PEP PEP Energy-harvesting Steps

NADH NADH

ATP BPG BPG

ADP G3P G3P NAD+ NAD+ ADP ADP

–2 ATP Energy-investment Step

ATP ATP glucose Glycolysis 3PG E3 E2 E1

(22)

Glycolysis

A D P

2

Oxidation of G3P occurs as

NAD+_{receives high-energy}

electrons.

Oxidation of 3PG occurs by removal of water.

Two molecules of pyruvate are the end products of glycolysis.

pyruvate pyruvate

ATP

+2 ATP

(net gain)

ATP

+2 ATP ATP

3PG

PEP PEP

ADP ADP

Energy-harvesting Steps

NADH NADH

ATP

BPG BPG

ADP G3P G3P NAD+ NAD+ ADP ADP

–2 ATP

ATP ATP

glucose Glycolysis 3PG E4 E3 E2 E1

(23)

Substrate-level ATP Synthesis

23

enzyme

ADP

ATP BPG

(24)

8.3 Outside the Mitochondria:

Fermentation

• Pyruvate

is a pivotal metabolite in cellular

respiration

• If O

₂

is not available to the cell,

fermentation

, an anaerobic process,

occurs in the cytoplasm.



During fermentation, glucose is incompletely

metabolized to lactate, or to CO

₂

and alcohol

(depending on the organism).

• If O

₂

is available to the cell, pyruvate

enters the mitochondria for aerobic

(25)

Outside the Mitochondria:

Fermentation

• Fermentation is an anaerobic process that reduces

pyruvate to either lactate or alcohol and CO₂

• NADH transfers its electrons to pyruvate

• Alcoholic fermentation, carried out by yeasts, produces

carbon dioxide and ethyl alcohol

 Used in the production of alcoholic spirits and breads.

• Lactic acid fermentation, carried out by certain bacteria

and fungi, produces lactic acid (lactate)

 Used commercially in the production of cheese, yogurt, and

sauerkraut.

• Other bacteria produce chemicals anaerobically,

including isopropanol, butyric acid, proprionic acid, and acetic acid.

(26)

Fermentation

26

2

4

2

glucose – 2 ATP ATP

E1

G3P

2NAD;

2 NADH

Plants

2CO 2

Animals

2 alcohol or

2 lactate ATP

ATP + 4

2ADP

E2

BPG 4ADP

E3

pyruvate

(net gain)

E4 ATP

(27)

Fermentation Helps Produce

Numerous Food Products

27

(28)

Fermentation Helps Produce

Numerous Food Products

(29)

Fermentation Helps Produce

Numerous Food Products

(30)

Outside the Mitochondria:

Fermentation

• Advantages

 Provides a quick burst of ATP energy for muscular activity.

• Disadvantages

 Lactate and alcohol are toxic to cells.

 Lactate changes pH and causes muscles to fatigue.

• Oxygen debt

 Yeast die from the alcohol they produce by fermentation

• Efficiency of Fermentation

 Two ATP produced per glucose of molecule during fermentation

is equivalent to 14.6 kcal.

 Complete oxidation of glucose can yield 686 kcal.

 Only 2 ATP per glucose are produced, compared to 36 or 38

ATP molecules per glucose produced by cellular respiration.

(31)

Outside the Mitochondria:

Fermentation

31

Fermentation

inputs outputs

2 lactate or

2 alcohol and 2 CO₂ glucose

2 ADP + 2 P 2 ATP net gain

(32)

8.4 Inside the Mitochondria

• The

Preparatory (prep) Reaction

 Connects glycolysis to the citric acid cycle

 End product of glycolysis, pyruvate, enters the

mitochondrial matrix

 Pyruvate is converted to a 2-carbon acetyl group

• Attached to Coenzyme A to form acetyl-CoA

• Electrons are picked up (as hydrogen atom) by NAD+

• CO₂ is released and transported out of mitochondria into the cytoplasm

(33)

Inside the Mitochondria

33

2 NAD+ _{2 NADH}

2 + 2 CoA 2 + 2 CO₂

2 pyruvate

O OH

C

CH

3

+ 2 CoA

CoA

CH ₃ pyruvate

carbon dioxide acetyl CoA

C O

C O

2 acetyl CoA + 2 carbon

(34)

Mitochondrion Structure and Function

34

Cristae: location of the electron transportchain (ETC)

Matrix: location of the prep reaction and the citric acid cycle outer

membrane inner membrane

intermembrane space

cristae matrix

(35)

Inside the Mitochondria

• Citric Acid Cycle

 Also called the Krebs cycle

 Occurs in the matrix of mitochondria

 Begins with the addition of a two-carbon acetyl

group (from acetyl-CoA) to a four-carbon molecule (oxaloacetate), forming a six-carbon molecule (citric acid)

 NADH and FADH₂ capture energy rich electrons

 ATP is formed by substrate-level phosphorylation

 Turns twice for one glucose molecule (once for

each pyruvate)

 Produces 4 CO₂, 2 ATP, 6 NADH and 2 FADH₂ per

glucose molecule

(36)

Citric Acid Cycle

2

e– e–

1. The cycle begins when a C₂acetyl group carried by CoA combines with a C₄ molecule to form citrate. acetyl CoA C₂ oxaloacetate C₂ CoA Glycolysis

glucose pyruvate Preparatory reaction

Electron transport chain and chemiosmosis Matrix Citric acid cycle NADH and FADH2 e– e– e– e– e– 2 ATP 2 ADP net ATP

4 ADP 4 ATP total

2ADP 2 ATP 32ADP

(37)

Citric Acid Cycle

2

e– e–

1. The cycle begins when a C₂acetyl group carried by CoA combines with a C₄ molecule to form citrate. acetyl CoA C2 oxaloacetate C₂ citrate C₆ CoA Glycolysis

Electron transport chain and chemiosmosis Matrix Citric acid cycle NADHand FADH2 e– e– e– e– e– 2 ATP 2 ADP net ATP 4 ADP 4 ATP total

2ADP 2 ATP 32ADP

(38)

Citric Acid Cycle

2

e–

2. Twice over, substrates are oxidized as NAD+ _is

Reduced to NADH, and CO2 is released.

1. The cycle begins when a C2 acetyl group carried by

CoA combines with a C4

molecule to form citrate. acetyl CoA C2 oxaloacetate C2 citrate C6 NAD NADH CoA ketoglutarate C5 CO2 Glycolysis

2ADP 2 ATP 32ADP

or 34 32 _{or 34} ATP

NADH

(39)

Citric Acid Cycle

2

e–

3. ATP is produced as an energized phosphate is transferred from a substrate to ADP.

molecule to form citrate. acetyl CoA C2 oxaloacetate C2 citrate C6 NAD ATP succinate C4 NADH CoA ketoglutarate C5 NAD+ NADH CO2 CO2 Glycolysis

2ADP 2 ATP 32ADP or 34 32

or 34 ATP NADH

NADH

(40)

Citric Acid Cycle

2

e–

molecule to form citrate.

4. Again a substrate is oxidized, but this time FAD is reduced to FADH2

acetyl CoA C2 oxaloacetate C2 citrate C6 NAD fumarate C4 FADH ATP succinate C4 NADH CoA ketoglutarate C5 NAD+ NADH CO2 FAD CO2 Glycolysis

2ADP 2 ATP 32ADP

or 34 32 _{or 34} ATP

NADH

(41)

Citric Acid Cycle

2

e–

molecule to form citrate.

5. Once again a substrate is oxidized, and NAD+

is reduced to NADH.

4. Again a substrate is oxidized, but this time FAD is reduced to FADH2

acetyl CoA C2 NADH oxaloacetate C2 citrate C6 NAD fumarate C4 NAD+ FADH ATP succinate C4 Citric acid cycle NADH CoA ketoglutarate C5 NAD+ NADH CO2 FAD CO2 Glycolysis

2ADP 2 ATP 32ADP or 34 32

or 34 ATP NADH

NADH

(42)

Inside the Mitochondria

42

inputs outputs

4 CO₂

NADH

FADH₂ 2

2 (2c) acetyl groups

6 NAD+

2 FAD

2 Citric acid cycle

P 2 ADP +2

6

ATP

(43)

Inside the Mitochondria

• Electron Transport Chain (ETC)

• Location:

 Eukaryotes: cristae of the mitochondria

 Aerobic prokaryotes: plasma membrane

• Series of carrier molecules:

 Pass energy-rich electrons successively from one to another

 Complex arrays of protein and cytochrome

• Cytochromes are proteins with heme groups with central iron atoms

• The electron transport chain

 Receives electrons from NADH & FADH₂

 Produces ATP by oxidative phosphorylation

• Oxygen serves as the final electron acceptor

 Oxygen combines with hydrogen ions to form water

(44)

Inside the Mitochondria

• The fate of the hydrogens:

 Hydrogens from NADH deliver enough energy to

make 3 ATPs

 Those from FADH₂ have only enough for 2 ATPs

 “Spent” hydrogens combine with oxygen

• Recycling of coenzymes increases efficiency

 Once NADH delivers hydrogens, it returns (as NAD+)

to pick up more hydrogens

 However, hydrogens must be combined with oxygen

to make water

 If O₂ is not present, NADH cannot release H+

 No longer recycled back to NAD+

(45)

45

Inside the Mitochondria

• The electron transport chain complexes pump H+_{from the}

matrix into the intermembrane space of the mitochondrion

• H+_{therefore becomes more concentrated in the}

intermembrane space, creating an electrochemical gradient.

• ATP synthase allows H+_{to flow down its gradient.}

• Flow of H+_{drives the synthesis of ATP from ADP and}

inorganic phosphate by ATP synthase.

• This process is called chemiosmosis

 ATP production is linked to the establishment of the H+_gradient

• ATP moves out of mitochondria and is used for cellular work

 It can be broken down to ADP and inorganic phosphate

 These molecules are returned to the mitochondria for more ATP

(46)

Organization and Function of the

Electron Transport Chain

2 O2 1 2 + 2 P H+

e :

Electron transport chain

high energy electron ATP channel protein Intermembrane space ATP synthase complex low energy electron cytochrome oxidase cytochrome c NADH-Q reductase cytochrome reductase coenzyme Q NADH Matrix FADH2 FAD + NAD+ 2 e-

2 ADP 32 ADP ATP or 34 4 ADP

net ATP 4 ATP total

2ADP 2ATP Glycolysis glucose pyruvate

Preparatory reaction Citric acid cycle Electron transport chain and chemiosmosis NADH and FADH2 NADH NADH e

- e- e- e- e- e- 32 or 34 H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+

ATP ADP H2O

(47)

Inside the Mitochondria

• Energy yield from glucose metabolism:

 Net yield per glucose:

• From glycolysis – 2 ATP

• From citric acid cycle – 2 ATP

• From electron transport chain – 32 or 34 ATP

 Energy content:

• Reactant (glucose) 686 kcal • Energy yield (36 ATP) 263 kcal • Efficiency is 39%

• The rest of the energy from glucose is lost as heat

(48)

Accounting of Energy Yield per

Glucose Molecule Breakdown

48

(49)

Accounting of Energy Yield per

Glucose Molecule Breakdown

49

Cy

top

lasm

Electron

transport

chain

2 net

glucose

2 pyruvate

glycolysis

NADH

2 4 or 6

(50)

Accounting of Energy Yield per

Glucose Molecule Breakdown

50

Cy

top

lasm

Ele

ctro

n

tran

spo

rt

cha

in

2 net

glucose

2 pyruvate

2 acetyl CoA

glycolysis

NADH

NADH 2

2

4 or 6

6 ATP

ATP

(51)

Accounting of Energy Yield per

Glucose Molecule Breakdown

51 Cy to pla s m E le c tron trans port c hai n 2 net 2 glucose 2 pyruvate

2 acetyl CoA

Citric acid cycle

glycolysis

2 CO2

NADH NADH NADH FADH2 2 2 6 2

4 or 6

6

18

4

(52)

Accounting of Energy Yield per

Glucose Molecule Breakdown

52 Cy to pla s m E le c tron trans port c hai n 2 net 2 glucose 2 pyruvate

2 acetyl CoA

subtotal subtotal glycolysis NADH NADH NADH 2 2 6 2

4 or 6

6 18 4 32 4 or 34

ATP ATP ATP 4CO₂ 2CO2 FADH2

6O₂ 6HO₂

(53)

Accounting of Energy Yield per

Glucose Molecule Breakdown

53 C y top las m M it oc ho nd ri on E lec tron trans po rt ch ain 2 net 2 glucose 2 pyruvate

2 acetyl CoA

Citric acid cycle

subtotal subtotal

glycolysis

2 CO₂

4 CO₂

NADH NADH NADH FADH₂ 2 2 6 2

4 or 6

6

18

4

32 4

36 or 38 total

6 O₂ 6 H₂O

ATP ATP ATP ATP ATP ATP ATP ATP ATP or 34

(54)

8.5 Metabolic Pool

• Foods:

 Sources of energy rich molecules

 Carbohydrates, fats, and proteins

• Degradative reactions (

Catabolism

) break down

molecules

 Tend to be exergonic (release energy)

• Synthetic reactions (

anabolism

) build molecules

 Tend to be endergonic (consume energy)

(55)

The Metabolic Pool Concept

55

ATP

ATP Electron

transport chain

proteins carbohydrates fats

amino acids

glucose fatty

acids glycerol

acetyl CoA Glycolysis

pyruvate

ATP Citric

acid cycle

(56)

Metabolic Pool

• Glucose is broken down in cellular respiration.

• Fat breaks down into glycerol and three fatty

acids.

• Amino acids break down into carbon chains and

amino groups

 Deamination (NH₂ removed) occurs in the liver

• Results in poisonous ammonia (NH₃) • Quickly converted to urea

 Different R-groups from amino acids are processed

differently

 Fragments enter respiratory pathways at many

different points

(57)

Metabolic Pool

• All metabolic compounds are part of the

metabolic pool

• Intermediates from respiratory pathways can be

used for

anabolism

• Anabolism (synthetic reactions of metabolism):

 Carbohydrates

• Start with acetyl-CoA

• Basically reverses glycolysis (but different pathway)

 Fats

• G3P converted to glycerol

• Acetyl groups are connected in pairs to form fatty acids

(58)

Metabolic Pool

• Anabolism (cont.):



Proteins:

• Made up of combinations of 20 different amino acids

• Some amino acids (11) can be synthesized by adult humans

• However, other amino acids (9) cannot be synthesized by humans

– Essential amino acids

– Must be present in the diet

(59)

Photosynthesis vs. Cellular

Respiration

59

O2

enzymes grana

Photosynthesis

NADP+

CH2O

NADPH

CO2

enzyme-catalyzed reactions

NADH

enzymes H2O

membrane

ATP production via chemiosmosis

ADP ATP

H2O

membrane

Cellular Respiration

NAD+

cristae