Water behind a dam represents _____ energy.

A) Kinetic

B) Electrical

C) Potential

D) Heat

E) Electromagnetic

The “powerhouse of the cell” is the_________.

A) Nucleus.

B) Mitochondrion.

C) Golgi complex.

D) Ribosome.

E) None of these

Mitochondrial structure review

Cellular respiration provides us with the energy we use

Slow-twitch muscles have more mitochondria than fast-twitch

Cellular Respiration

All Living Things Require and Consume Energy

• Ultimate source of energy for all life on earth is the sun

• We get our energy from food

C6H12O6(s) + 6O2(g) 6CO2(g)+ 6H2O(l)

This is a combustion reaction

Combustion is a kind of redox reaction

Aerobic respiration of glucose is the most basic means for cells to acquire energy

Respiration interacts with photosynthesis in the recycling of

carbon

Respiration at the cellular level necessitates our breathing

The more our cells respire, the more oxygen we need

Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with glucose:

C6H12O6(s) + 6O2(g) 6CO2(g)+ 6H2O(l) + Energy (ATP + heat)

Respiration is a REDOX reaction

Oxidation-Reduction Reactions

• Cellular respiration is a redox reaction

• Involves the exchange of electrons

• Oxidation- the loss of electrons

• Reduction- the gain of electrons (reduction of charge

• Na + Cl Na+ + Cl-

• Which is oxidized? Which is reduced?

Redox does not require complete loss or gain of electrons

becomes reduced

becomes reduced

Reactants

becomes oxidized

becomes reduced

Products

Methane(reducing

agent)

Oxygen(oxidizing

agent)

Carbon dioxide Water

CH4 2 O2+ ++CO2Energy 2 H2O

During cellular respiration, glucose is oxidized and oxygen is

reduced

C6H12O6 + 6O2 6CO2 + 6H2O + Energy

becomes oxidized

becomes reduced

Electrons bound to more electronegative atoms are lower in energy

• The energy heirarchy of carbon bonds:CH4 CH3OH CH2O HCOOH

CO2

Electrons in reduced molecules have higher energy than those in oxidized molecules

C6H12O6(s) + 6O2(g) 6CO2(g)+ 6H2O(l)

The cell must control this reaction

Aerobic respiration of glucose is the most basic means for cells to acquire energy

Oxidation is the ______, and reduction is the __________.

 

A) gain of electrons . . . loss of electrons  

B) loss of electrons . . . gain of electrons  

C) loss of oxygen . . . gain of oxygen  

D) gain of oxygen . . . loss of oxygen  

E) gain of protons . . . loss of protons

The Stages of Cellular Respiration: A Preview

• Cellular respiration has three stages:– Glycolysis

– The citric acid cycle (a.k.a. the Krebs cycle)

– Oxidative phosphorylation (using the electron transport chain)

LE 9-6_1

Mitochondrion

Glycolysis

PyruvateGlucose

Cytosol

ATP

Substrate-levelphosphorylation

LE 9-6_2

Mitochondrion

Glycolysis

PyruvateGlucose

Cytosol

ATP

Substrate-levelphosphorylation

ATP

Substrate-levelphosphorylation

Citricacidcycle

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

Overview of respiration

• Glycolysis: Glucose is split, 2 pyruvates are formed, a little ATP is gained (by substrate-level phosporylation)

• The Citric Acid Cycle: Redox molecules NAD+ and FAD are charged up, a little ATP is gained

• Oxidative phosphorylation: Lots of ATP is made by ATP synthase

Processes important to respiration

• Substrate-level phosphorylation to form ATP

• Recycling of the Redox molecules NAD+ and FAD to carry electrons to the e- transport chain

• The electron transport chain, which helps generate much ATP

Substrate-level phosphorylation

Making ATP by taking a phosphate from something and sticking it onto an ADP

Recycling of NAD+

The e- transport chain generates a proton gradient

Step 1: Glycolysis

In: 1 glucose, 2 NAD+

Out: 2 ATP (net), 2NADH, 2 pyruvate

Glycolysis converts glucose to pyruvate

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

• Glycolysis occurs in the cytoplasm and has two major phases:– Energy investment phase– Energy payoff phase

Animation: Glycolysis

Overview of Glycolysis

• 10- step process• Glucose (6C) 2 Pyruvate ( 3 C ea.)• 2 ATPs net profit• 2 NAD+’s are charged

LE 9-9a_1

Glucose

ATP

ADP

Hexokinase

ATP ATP ATP

Glycolysis Oxidationphosphorylation

Citricacidcycle

Glucose-6-phosphate

LE 9-9a_2

Glucose

ATP

ADP

Hexokinase

ATP ATP ATP

Glycolysis Oxidationphosphorylation

Citricacidcycle

Glucose-6-phosphate

Phosphoglucoisomerase

Phosphofructokinase

Fructose-6-phosphate

ATP

ADP

Fructose-1, 6-bisphosphate

Aldolase

Isomerase

Dihydroxyacetonephosphate

Glyceraldehyde-3-phosphate

LE 9-9b_1

2 NAD+

Triose phosphatedehydrogenase

+ 2 H+

NADH2

1, 3-Bisphosphoglycerate

2 ADP

2 ATPPhosphoglycerokinase

Phosphoglyceromutase

2-Phosphoglycerate

3-Phosphoglycerate

LE 9-9b_2

2 NAD+

Triose phosphatedehydrogenase

+ 2 H+

NADH2

1, 3-Bisphosphoglycerate

2 ADP

2 ATPPhosphoglycerokinase

Phosphoglyceromutase

2-Phosphoglycerate

3-Phosphoglycerate

2 ADP

2 ATPPyruvate kinase

2 H2OEnolase

Phosphoenolpyruvate

Pyruvate

Energetics of Glycolysis

Concept 9.3: The citric acid cycle completes the energy-yielding oxidation of organic

molecules

• Before the citric acid cycle can begin, pyruvate must be converted to acetyl CoA, which links the cycle to glycolysis

Before the citric acid cycle, pyruvate is fastened to

Co-Enzyme A

Step 2: Citric Acid cycle

In: Acetyl CoA, NAD+, FAD, ADP

Out: CO2, NADH, FADH, some ATP

• In the citric acid cycle, electrons are ripped from carbon onto the redox molecules NAD+ and FAD

• All carbon is converted to CO2

• A little bit of ATP is generated

• The citric acid cycle, also called 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

• The citric acid cycle has eight steps, each catalyzed by a specific enzyme

LE 9-11Pyruvate(from glycolysis,2 molecules per glucose)

ATP ATP ATP

Glycolysis Oxidationphosphorylation

CitricacidcycleNAD+

NADH

+ H+

CO2

CoA

Acetyl CoACoA

CoA

Citricacidcycle

CO22

3 NAD+

+ 3 H+

NADH3

ATP

ADP + P i

FADH2

FAD

LE 9-12_4

ATP ATP ATP

Glycolysis Oxidationphosphorylation

Citricacidcycle

Citricacidcycle

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 3: Oxidative Phosphorylation

In which the electron transport chain generates a proton gradient, and ATP synthase makes tons of

ATP

Oxidative phosphorylation

• Electron-carrying redox molecules (NADH and FADH2) transfer their electrons to the e- transport chain

• The e- transport chain uses the electrons to create a proton gradient across the inner mitochondrial membrane

• ATP synthase uses the potential energy in the proton gradient to convert much ADP into ATP

LE 9-13

ATP ATP ATP

GlycolysisOxidative

phosphorylation:electron transportand chemiosmosis

Citricacidcycle

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

The electron transport chain uses electrons to generate a proton gradient

Intermembranespace

Innermitochondrialmembrane

Mitochondrialmatrix

Proteincomplex Electron

carrier

Electronflow

NADH NAD

FADFADH2

H

H

HH

H2O

H

H

ATPsynthase

2O212

H

PADP ATP

Electron Transport Chain Chemiosmosis

OXIDATIVE PHOSPHORYLATION

H

H

H

H

H

H

H

Some poisons can disrupt e- transport

• The energy stored in a H+ gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis

• The H+ gradient is referred to as a proton-motive force, emphasizing its capacity to do work

Animation: Fermentation Overview

LE 9-14

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.

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

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:

During cellular respiration, NADH  

A) is converted to NAD+ by an enzyme called dehydrogenase.  

B) is chemically converted into ATP.  

C) is reduced to form NAD+.  

D) delivers its electron load to the electron transport chain.  

E) None of the choices are correct.

Oxygen is the final e- resting place in the chain

Human cells can do glycolysis faster than human lungs can

take in oxygen

Q: What happens if there is not enough oxygen?

A: It depends on what kind of creature you are…

Without O2, yeast make alcohol

Humans make lactic acid instead of ethanol

Lactic Acid in muscles creates a burning sensation

• Overworked muscles can become anoxic

• In low oxygen environments, pyruvate is converted to lactate to regenerate NAD+

• Lactic acid causes great suffering

LE 9-17a

CO2

+ 2 H+

2 NADH2 NAD+

2 Acetaldehyde

2 ATP2 ADP + 2 P i

2 Pyruvate

2

2 Ethanol

Alcohol fermentation

Glucose Glycolysis

LE 9-17b

CO2

+ 2 H+

2 NADH2 NAD+

2 ATP2 ADP + 2 P i

2 Pyruvate

2

2 Lactate

Lactic acid fermentation

Glucose Glycolysis

Fermentation and Cellular Respiration Compared

• Both processes use glycolysis to oxidize glucose and other organic fuels to pyruvate

• The processes have different final electron acceptors: an organic molecule (such as pyruvate) in fermentation and O2 in cellular respiration

• Cellular respiration produces much more ATP

LE 9-18

Pyruvate

Glucose

CYTOSOL

No O2 presentFermentation

Ethanolor

lactate

Acetyl CoA

MITOCHONDRION

O2 present Cellular respiration

Citricacidcycle

The Evolutionary Significance of Glycolysis

• Glycolysis occurs in nearly all organisms• Glycolysis probably evolved in ancient prokaryotes

before there was oxygen in the atmosphere

Glycolysis and the citric acid cycle connect to many other

metabolic pathways

• Gycolysis and the citric acid cycle are major intersections to various catabolic and anabolic pathways

Metabolism can build up, or break down

LE 6-15ATP needed to drive biosynthesis

ATP

CITRICACID

CYCLE

AcetylCoA

Aminogroups

Proteins

Amino acids Fatty acids Glycerol

Fats

Cells, tissues, organisms

Carbohydrates

Sugars

GLUCOSE SYNTHESIS

Pyruvate G3P Glucose

The Versatility of Catabolism• Catabolic pathways funnel electrons from many

kinds of organic molecules into cellular respiration• Glucose- 4 calories/gram• Proteins- 4 calories/gram• Fats- 9 calories/gram

• Which of the following processes produces the most ATP per molecule of glucose oxidized?  

A) aerobic respiration  

B) anaerobic respiration  

C) alcoholic fermentation  

D) lactic acid fermentation  

E) All produce approximately the same amount of ATP per molecule of glucose