Respiration Cellular respiration is the process by which cells transfer chemical energy from sugar...

Respiration• Cellular respiration is the process by which

cells transfer chemical energy from sugar molecules to ATP molecules.

• As this happens cells release CO2 and use up O2

• Respiration can be AEROBIC or ANAEROBIC

Breathing supplies oxygen to our cells and removes carbon dioxide

– Breathing provides for the exchange of O2 and CO2

Between an organism and its environment

CO2

CO2

O2

O2Bloodstream

Muscle cells carrying out

Cellular Respiration

Breathing

Glucose O2

CO2 H2O ATP

Lungs

Figure 6.2

.

The human body uses energy from ATP for all its activities. – ATP powers almost all cellular and body activities

CELLULAR RESPIRATION• Cellular respiration is an energy- releasing

process. It produces ATP• ATP is the universal energy source Making ATP

• Plants make ATP during photosynthesis

• Cells of all organisms make ATP by

breaking down carbohydrates, fats, and

protein

– The energy in an ATP molecule• Lies in the bonds between its phosphate groups

Phosphategroups

ATP

EnergyP P PP P PHydrolysis

Adenine

Ribose

H2O

Adenosine diphosphateAdenosine Triphosphate

++

ADP

Figure 5.4A

REDOX REACTIONS

– The loss of electrons is called oxidation.

– The addition of electrons is called reduction

Overview of Aerobic Respiration

C6H12O6 + 6O2 6CO2 + 6H2O +ATP

glucose oxygen carbon water

dioxide

– When glucose is converted to carbon dioxide• It loses hydrogen atoms, which are added to

oxygen, producing water

C6H12O6 6 O26 CO2 6 H2O

Loss of hydrogen atoms (oxidation)

Gain of hydrogen atoms (reduction)

Energy

(ATP)Glucose

+ + +

Figure 6.5A

STAGES OF CELLULAR RESPIRATION

Overview: Cellular respiration occurs in three main stages

1. Glycolysis

2. Krebs Cycle or Citric Acid Cycle

3. Electron Transport Chain or Phosphorylation

– Stage 1:

Glycolysis– No oxygen needed. It is universal

• Occurs in the cytoplasm

• Breaks down glucose into pyruvate, producing a small amount of ATP (2)

GLYCOLYSIS• Where?: In the cytosol of all cells.Both aerobic and anaerobic respiration begin with glycolysis.• What happens?: The cell harvests energy by oxidizing glucose

to pyruvate.• One molecule of glucose (6 carbons) is converted to two

pyruvate molecules (3 carbons) through a series of 10 reactions mediated by enzymes.

• Result: 2 pyruvate molecules (each with a 3 carbon backbone) 2 NADH molecules. Carrier that picks up hydrogens

stripped from glucose. 2 ATP molecules. 4 are made but cells use 2 to start

glycolysis so net gain is 2

An overview of cellular respiration

Preparatory steps to enter the Krebs cycle

• The 2 pyruvate molecules enter the mitochondrion and an enzyme strips one carbon from each pyruvate.

• This two carbon molecule is picked up by Co-enzyme A in preparation for the Krebs cycle.

• This is acetyl CoA. This is what enters the Krebs cycle: C-C-CoA (oxaloacetate)

Stage 2 :

The citric acid cycle or Krebs cycle

• Takes place in the mitochondria

• Completes the breakdown of glucose (catabolism), producing a small amount of ATP (2ATP)

• Pyruvate is broken down to carbon dioxide

• More coenzymes are reduced .Supplies the third stage of cellular respiration with electrons (hydrogen carriers such as NADH)

KREBS CYCLE or citric acid cycle • This cycle involves a series of 8 steps forming and

rearranging. Each time it releases CO2 and NADH carries hydrogen to the last step. 6 CO2 are given off as waste (this is the most oxidized form of Carbon)In total:

6 CO2

6 NADH are produced and

2 FADH and only

2 ATP

An overview of cellular respiration

Stage 3:

Oxidative phosphorylation or electron transport chain

• Occurs in the mitochondria (inner membrane)

• Uses the energy released by “falling” electrons to pump H+ across a membrane

• Harnesses the energy of the H+ gradient through chemiosmosis, producing ATP

Chemiosmosis

Chemiosmosis is an energy coupling mechanism that uses energy stored on H+

Chemiosmosis is the coupling of the REDUX reactions of the electron transport chain to ATP synthesis

– NADH passes electrons to an electron transport chain

– As electrons “fall” from carrier to carrier and finally to O2

• Energy is released in small quantities

H2O

NAD

NADH

ATP

H

H

Controlled release of energy for synthesis

of ATPElectron

transport chain

2 O2

2e

2e

12

Figure 6.5C

ELECTRON TRANSPORT CHAIN

• Electron transport systems are embedded (protein

molecules) in inner mitochondrial membranes (cristae)

• NADH and FADH2 give up electrons that they

picked up in earlier stages to electron transport

system

• Electrons are transported through the system

• The final electron acceptor is oxygen. The

hydrogen combines with the oxygen to form water

Electron transport chain

Intermembrane space

Inner mitochondrial membrane

Mitochondrial matrix

Protein complex

Electron flow

Electron carrier

NADH NAD+

FADH2 FAD

H2OATPADP

ATP synthase

H+ H+ H+

H+

H+H+

H+

H+

H+

H+

H+

H+

H+

H+

P

O2

Electron Transport Chain Chemiosmosis

.

OXIDATIVE PHOSPHORYLATION

+ 212

Figure 6.10

An overview of cellular respiration (Layer 3)An overview of cellular respiration (Layer 3)

HOW MUCH TOTAL ATP(ENERGY) WAS PRODUCED?

• Glycolysis

2 ATP formed by substrate-level phosphorylation

• Krebs cycle and preparatory reactions

2 ATP formed by substrate-level phosphorylation

• Electron transport phosphorylation

32-34 ATP formed

2+2+34=38

Most ATP production occurs by oxidative phosphorylation or electron transport chain

WHY OXYGEN?

• Electron transport phosphorylation requires the presence of oxygen

• Oxygen withdraws spent electrons from the electron transport system, then combines with H+ to form water

Web site tutorials to check:

• http://www.sp.uconn.edu/~terry/Common/respiration.html

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

• http://www.wisc-online.com/objects/MBY2604/MBY2604.swf

An overview of cellular respiration

An overview of cellular respiration

An overview of cellular respiration (Layer 3)An overview of cellular respiration (Layer 3)

Animation: Cell Respiration OverviewAnimation: Cell Respiration Overview

How efficient is cellular respiration?

• Only about 40% efficient.

In other words, a call can harvest about 40% of the energy stored in glucose.

• Most energy is released as heat

Evolution of cellular respiration

• When life originated, atmosphere had little oxygen

• Earliest organisms used anaerobic pathways

• Later, photosynthesis increased atmospheric

oxygen

• Cells arose that used oxygen as final acceptor in

electron transport (without oxygen to act as the final

hydrogen acceptor the cells will die)

Fermentation

• Fermentation allows some cells to produce ATP without oxygen.

• This is Anaerobic respiration

ANAEROBIC RESPIRATIONFermentation is an anaerobic alternative

to cellular respiration• Do not use oxygen

• Produce less ATP( 2) than aerobic pathways

• Two types. One produces alcohol and the

other lactic acid as waste products

– Fermentation pathways

– Anaerobic electron transport

Fermentation– Under anaerobic conditions, many kinds of cells

can use glycolysis alone to produce small amounts of ATP

• Begin with glycolysis

• Do not break glucose down completely to carbon

dioxide and water

• Yield only the 2 ATP from glycolysis

• Steps that follow glycolysis serve only to regenerate

NAD+

Yeast

• Single-celled fungi

• Carry out alcoholic fermentation

• Saccharomyces cerevisiae– Baker’s yeast– Carbon dioxide makes bread dough rise

• Saccharomyces ellipsoideus– Used to make beer and wine

Our muscle cells…• In the absence of oxygen our muscles can

carry out fermentation, but the pyruvate from glycolysis is turned into lactic acid instead of alcohol

– In alcohol fermentation• NADH is oxidized to NAD+ while converting

pyruvate to CO2 and ethanol

NAD NADH NADH NAD2 2 2 2

GLYCOLYSIS

2 ADP 2 P ATP

Glucose 2 Pyruvate

releasedCO2

2 Ethanol

22

Figure 6.13B

Figure 6.13C

More details…

Two stages of glycolysis

• Energy-requiring steps

– ATP energy activates glucose and its six-

carbon derivatives

• Energy-releasing steps

– The products of the first part are split into

three-carbon pyruvate molecules

– ATP and NADH form

•Glycolysis harvests chemical energy by oxidizing glucose to pyruvate

– In glycolysis, ATP is used to prime a glucose molecule

• Which is split into two molecules of pyruvate

NAD NADH H

Glucose2 Pyruvate

ATP2P2 ADP

22

2

2

+

+

Figure 6.7A

– In the first phase of glycolysis • ATP is used to energize a glucose molecule,

which is then split in two

ATP

Glucose PREPARATORY PHASE

(energy investment)

ADP

Step

Glucose-6-phosphate

Fructose-6-phosphate

P

P

Fructose-1,6-diphosphate

ATP

ADP

PP

 Steps      –   A fuel molecule is energized, using ATP.

 Step      A six-carbon intermediate splits into two three-carbon intermediates.

1

2

3

44

1 3

Figure 6.7C

Pyruvate

ATP

ADP

ATP

ADP

P

ATP ATP

ADP ADP

P

2-Phosphoglycerate

P

H2O H2O

Phosphoenolpyruvate(PEP)

 Steps     –      ATP and pyruvate are produced.

P 3 -Phosphoglycerate

P

P

9 9

6 6

7 7

8 8

6 9 Step     A redox reaction generates NADH.

P

NADH NADHP

P P P P

P

+H+H

ENERGY PAYOFF PHASE

Glyceraldehyde-3-phosphate(G3P)

1,3 -Diphosphoglycerate

P

5

6 9

5 5

66

7 7

88

9 9

NAD NAD

– In the second phase of glycolysis• ATP, NADH, and pyruvate are formed

Net Energy Yield from Glycolysis

Energy requiring steps:

2 ATP invested

Energy releasing steps:

2 NADH formed

4 ATP formed

Glycolysis net yield is 2 ATP and 2 NADH

Preparatory reactions before the Krebs cycle

• Preparatory reactions– Pyruvate is oxidized into two-carbon acetyl units and

carbon dioxide– NAD+ is reduced

pyruvate + coenzyme A + NAD+

acetyl-CoA + NADH + CO2

• One of the carbons from pyruvate is released in CO2

• Two carbons are attached to coenzyme A and continue on to the Krebs cycle

CO2

Pyruvate

NAD NADH H

CoA

Acetyl CoA(acetyl coenzyme A)

Coenzyme A

Figure 6.8

Pyruvate is gets ready for the citric acid cycle– Prior to the citric acid cycle

• Enzymes process pyruvate, releasing CO2 and producing NADH and acetyl CoA

1

2

3

Krebs cycle– The acetyl units are oxidized to carbon dioxide– NAD+ and FAD are reduced

Products:• Coenzyme A

• 2 CO2

• 3 NADH

• FADH2

• ATP

The citric acid cycle (Krebs)completes the oxidation of organic fuel (glucose), generating many NADH and FADH2 molecules

– In the citric acid cycle• The two-carbon acetyl part of acetyl CoA is oxidized

CoA

CoA

CO2

NAD

NADHFAD

FADH2

ATP P

CITRIC ACID CYCLE

ADP

3

3

3 H

Acetyl CoA

2

Figure 6.9A

Krebs Cycle or Citric Acid Cycle

For each turn of the Krebs cycle

• Two CO2 molecules are released (All of the

carbon molecules in pyruvate end up in carbon dioxide)• Three NADH and one FADH2 (Coenzymes are

reduced, they pick up electrons and hydrogen)

• One molecule of ATP is formed for each turn so the net yield of ATP for the Krebs or Citric Acid cycle is 2 ATP molecules.

What happened to co-enzymes (NAD and FAD) during the first two stages?

Co-enzymes were reduced (gained electrons)

• Glycolysis 2 NADH• Preparatory

reactions 2 NADH• Krebs cycle 2 FADH2 + 6 NADH

• Total 2 FADH2 + 10 NADH

Most ATP production occurs by oxidative phosphorylation or electron transport chain

– Electrons from NADH and FADH2 • Travel down the electron transport chain to oxygen,

which picks up H+ to form water

– Energy released by the redox reactions• Is used to pump H+ into the space between the

mitochondrial membranes

ELECTRON TRANSPORT CHAIN OR PHOSPHORYLATION

• Takes place in the mitochondria• Coenzymes deliver electrons to electron

transport systems• Electron transport sets up H+ ion gradients• Flow of H+ down gradients powers ATP

formation• The net yield from oxidative

phosphorilation is 32 to 34 ATP molecules

Making ATP : Chemiosmotic model

– In chemiosmosis, the H+ diffuses back through the inner membrane through ATP synthase complexes

• Driving the synthesis of ATP

Intermembrane space

Inner mitochondrial membrane

Mitochondrial matrix

Protein complex

Electron flow

Electron carrier

NADH NAD+

FADH2 FAD

H2OATPADP

ATP synthase

H+ H+ H+

H+

H+H+

H+

H+

H+

H+

H+

H+

H+

H+

P

O2

Electron Transport Chain Chemiosmosis

.

OXIDATIVE PHOSPHORYLATION

+ 212

Figure 6.10

Certain poisons interrupt critical events in cellular respiration

– Various poisons• Block the movement of electrons

• Block the flow of H+ through ATP synthase

• Allow H+ to leak through the membrane

H+

H+

H+

H+

H+

H+ H+ H+ H+

H+

H+

H+

H+

O2

H2OP ATP

NADH NAD+

FADH2 FAD

Rotenone Cyanide, carbon monoxide

Oligomycin

DNP

ATPSynthase

2

ADP

Electron Transport Chain Chemiosmosis

1

2

Figure 6.11

•Review: Each molecule of glucose yields many molecules of ATP

– Oxidative phosphorylation, using electron transport and chemiosmosis

• Produces up to 38 ATP molecules for each glucose molecule that enters cellular respiration

NADHNADH

NADH NADH FADH2

Cytoplasm

Electron shuttleacross membrane Mitochondrion

GLYCOLYSISGlucose Pyruvate

by substrate-level phosphorylation

by substrate-level phosphorylation

by oxidative phosphorylation

OXIDATIVE PHOSPHORYLATION

(Electron Transport and Chemiosmosis)

2 AcetylCoA

CITRIC ACIDCYCLE

2 ATP 2 ATP about 34 ATP

Maximum per glucose:About

38 ATP

2

2 6 2

2 2

(or 2 FADH2)

Figure 6.12

Anaerobic Electron Transport

• Carried out by certain bacteria

• Electron transport system is in bacterial plasma membrane

• Final electron acceptor is compound from environment (such as nitrate), NOT oxygen

• ATP yield is almost as good as from aerobic respiration

INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND

SYNTHESIS

• Cells use many kinds of organic molecules as fuel for cellular respiration

– Carbohydrates, fats, and proteins can all fuel cellular respiration

• When they are converted to molecules that enter glycolysis or the citric acid cycle

OXIDATIVEPHOSPHORYLATION

(Electron Transportand Chemiosmosis)

Food, such aspeanuts

Carbohydrates Fats Proteins

Sugars Glycerol Fatty acids Amino acids

Aminogroups

Glucose G3P Pyruvate AcetylCoA

CITRICACID

CYCLE

ATP

GLYCOLYSIS

Figure 6.14

How is energy obtained from proteins?

• Proteins are broken down to amino acids

• Amino acids are broken apart

• Amino group is removed, ammonia forms, is

converted to urea and excreted

• Carbon backbones can enter the Krebs cycle

How do we get energy from fats?

• Most stored fats are triglycerides

• Triglycerides are broken down to glycerol and

fatty acids

• Glycerol is converted to PGAL, an intermediate of

glycolysis

• Fatty acids are broken down and converted to

acetyl-CoA, which enters Krebs cycle

LE 9-19

Citricacidcycle

Oxidativephosphorylation

Proteins

NH3

Aminoacids

Sugars

Carbohydrates

Glycolysis

Glucose

Glyceraldehyde-3- P

Pyruvate

Acetyl CoA

Fattyacids

Glycerol

Fats

• Food molecules provide raw materials for biosynthesis

– Cells use some food molecules and intermediates from glycolysis and the citric acid cycle as raw materials

– This process of biosynthesis • Consumes ATP

ATP needed to drive biosynthesis

ATP

CITRICACID

CYCLE

GLUCOSE SYNTHESISAcetylCoA Pyruvate G3P Glucose

Aminogroups

Amino acidsFatty acids Glycerol Sugars

CarbohydratesFatsProteins

Cells, tissues, organisms

Figure 6.15

• The fuel for respiration ultimately comes from photosynthesis

– All organisms • Can harvest energy from organic molecules

– Plants, but not animals• Can also make these molecules from inorganic sources by the

process of photosynthesis

Figure 6.16

Electrons “fall” from organic molecules to oxygen during cellular respiration

• In cellular respiration, glucose and other fuels are oxidized, releasing energy.

• In the summary equation of cellular respiration: C6H12O6 + 6O2 6CO2 + 6H2O+ ATP

• Glucose is oxidized (loses electrons), oxygen is reduced ( gains electrons)

• Cellular respiration does not oxidize glucose in a single step that transfers all the hydrogen in the fuel to oxygen at one time.

glucose is broken down gradually in a series of steps, each catalyzed by a specific enzyme