Energy Releasing Pathways

ATP

Aerobic Respiration

•A redox process•Glucose contains energy

that can be converted to ATP

•Uses oxygen therefore aerobic

Cellular Energy Transfer• Cells transfer energy

by redox reactions• Remember:

– oxidation is the loss of electrons

– reductions is the gain of electrons

• Oxidation involves loss of energy

• Reduction involves the gain of energy

Aerobic Respiration- Redox

• C6H12O6 + 6 O2 + 6 H2O 6 CO2 + 12 H2O + Energy

• Water is both a reactant and a product

• Glucose is oxidized to form CO2

• C6H12O6 + 6 O2 + 6 H2O 6 CO2 + 12 H2O + Energy

• Oxygen is reduced, forming water

• C6H12O6 + 6 O2 + 6 H2O 6 CO2 + 12 H2O + Energy

• The electrons produced are used to form ATP

oxidation

reduction

                               

Aerobic Respiration- 4 Stages

•Glycolysis•Formation of acetyl coenzyme

A•Citric Acid Cycle•Electron transport system and

chemiosmosis

Glycolysis

•Glucose is converted to 2 3-carbon molecules of pyruvate

•ATP and NADH are formed•Occurs in the cytosol

•Yellow- products•Green- reactants

Glycolysis Pyruvate Yield• Glycolysis means “sugar splitting”• One 6-carbon molecule is converted to

two 3-carbon molecules• Occurs in cytosol• Occurs in both aerobic and anaerobic

conditions• A series of reactions; each catalyzed by

a different enzyme• Glucose yields two pyruvates

Glycolysis• First phase requires ATP

investment

G3P

2 ATPs used

Glucose

2 glyceraldehyde-3-phosphate (G3P)

Fructose- 1,6-diphosphate

2 ATPs used

PHASE 1

Glycolysis• Second phase yields NADH and

ATP

G3P

Pyruvate

G3P

Pyruvate

+ 2 NADH

+ 4 ATP

PHASE 2

Pyruvate to acetyl CoA

• A carboxyl group is removed from pyruvate (carbon dioxide is produced)

• NADH is produced• acetyl group joins with coenzyme A

forming acetyl CoA• Coenzyme A is made from

pantothenic acid

Pyruvate

acetyl CoA

Coenzyme A

+ NADH

+ CO2

Glycolysis

Krebs Cycle

acetyl CoA

Acetyl Coenzyme A

• Pyruvate is converted into acetyl CoA

• NADH is produced • Carbon dioxide is a waste product• Occurs in the mitochondria

•Yellow- products•Green- reactants

2 pyruvate + 2 NAD+ + 2 CoA ----> 2 acetyl CoA + 2 NADH + 2 carbon dioxide

Citric Acid Cycle• Oxidizes acetyl CoA• Also known as Krebs cycle• Occurs in mitochondria (matrix)• Series of steps ultimately

reforming oxaloacetate• All of the energy of glucose is

carried by NADH and FADH2

Citric Acid Cycle

• Acetyl CoA combines with oxaloacetate, forming citrate

• Citrate undergoes conversions, ultimately re-forming exaloacetate

• Carbon dioxide is a waste product• ATP, NADH, and FADH2 are

produced

Acetyl CoA

oxaloacetate

+ 6 NADH

+ 2 ATP

+ 2 FADH2

One Turn of Citric Acid Cycle*

1. 2C molecule enters the cycle & joins a 4C molecule.

2. In a series of steps, the remaining H and high energy e- are removed from the 2C.

3. 3 NAD+ are converted into 3 NADH & 3H+.

4. 1 FAD is converted into 1 FADH2.5. 1 ATP is made.6. 2 CO2 are released.7. At the end of the cycle, nothing remains

of the original glucose molecule. * remember…this is x2!

Types of Reactions

• Dehydrogenation– Hydrogens are transferred to a

coenzyme (NAD+ or FAD)• Decarboxylations

– Carboxyl groups are removed from the substrate as carbon dioxide

• Preparation reactions– molecules are rearranged in

preparation for decarboxylations or dehydrogenations

Electron Transport SystemChemiosmosis

• Electrons that originated in glucose are transferred via NADH and FADH2 to a chain of electron acceptors

• Hydrogen ions are pumped across the inner mitochondrial membrane

• ATP is produced by chemiosmosis

Electron Transport Chain• Coupled to ATP synthesis• Transports e- from NADH and

FADH2 to O2

Electrons FMN a series of cytochromes and coenzyme Q

Electron Carriers

• Most electron carriers carry hydrogen atoms

• Electron carriers transfer energy• Electrons lose energy as they are

transferred between acceptors• NAD+ is a common hydrogen acceptor

is respiratory and photosynthetic pathways– Nicotinamide adenine dinucleotide

Electron Carriers• Nicotine adenine dinucleotide

phosphate (NADP+) is involved in photosynthesis

NAD+ is a coenzyme derived from the vitamin nicotinic acid (niacin)

Electron Carriers• Flavin Adenine Dinucleotide- FAD+

is involved in cellular respiration

Electron Carriers• Cytochromes- proteins containing

iron

Electron Transport Chain

– Electrons lose energy as they pass through the chain

Electron Transport Chain– Hydrogen ions (protons) are passed

into the intermembrane space of the mitochondria

Electron Transport Chain

– Electrons are finally passed to oxygen thereby forming water

FMN

Q

cyt b

cyt cr

cyt c

cyt a

cyt a3

2H+

2H+

2H+

NADH

FADH 2

O 2 H 2O

Complex I

Complex II

Complex III

Chemiosmotic Model• 1978 Nobel Prize in

Chemistry for a 1961 paper on the chemiosmotic model

• Cornwall, UK• Glynn Research

Laboratories• Died in 1992

Peter Mitchell

Chemiosmotic model

• Explains the coupling of ATP synthesis to electron transport

• A proton gradient is formed across the inner mitochondrial membrane

Chemiosmotic Model

• Protons diffuse through the channels formed by the enzyme complex ATP synthase

• Movement of protons catalyze production of ATP

• Protons diffuse through the channels formed by the enzyme complex ATP synthase

• Movement of protons catalyze production of ATP

http://telstar.ote.cmu.edu/biology/animation/ATPSynthesis/biochem.html

Energy Yield• Efficiency is about 40%; the

rest is disseminated as heat• Maximum yield of ATPs

– from NADH- 3 ATP– from FADH2- 2 ATP

• The NADHs from glycolysis produce fewer ATPs due to the necessity of transport of NADH across the mitochondrial membrane

Energy Yield

The NADHs from glycolysis produce fewer ATPs due to the necessity of transport of NADH across the mitochondrial membrane

36 to 38 ATPs yield

GLUCOSE ATP produced

GLUCOSE

GLYCOLYSIS

2 ATPproduced directly

2 ATP

ACETYL CoA

GLUCOSE

GLYCOLYSIS

2 NADH

2 ATPproduced directly

2 ATP

6 ATPthrough electron transport

+

8 ATP

PYRUVIC ACID

2 NADH

6 ATPthrough electron transport

+

14 ATP

KREBS CYCLE

2 ATPproduced directly

+

16 ATP

6 NADH18 ATP

through electron transport

+

34 ATP

2 FADH24 ATP

through electron transport

+

38 ATP

Other Nutrients• Nutrients other that glucose

provide energy• Humans gain more energy from

oxidation of fatty acids than glucose– Lipids contain 9 kcal per gram– Lipids are broken down and glycerol

enters glycolysis; fatty acids are converted to acetyl CoA and enter the citric acid cycle

Other Nutrients

• Proteins are broken down into amino acids– Amino acids are deaminated (the

amino acids are removed)– The remaining carbon chain

centers at various points– Proteins contain about 4 kcal per

gram

Regulation of Aerobic Respiration

•ATP synthesis continues until ADP stores are depleted

•Enzyme regulation is important•An important regulation point is

phosphofructokinase

PFKPFK is the committed step in glycolysis. Once this step is done then glycolysis will carry through.

PFK is activated by ADP/AMP

PFK is inhibited by

ATP

low pH

citrate groups

Anaerobic Respiration

• Various inorganic substances serve as the final electron acceptor like sulfur

• Yield is only the two ATP molecules from glycolysis

• Seen is some bacteria

Alcoholic Fermentation

• Produces ethanol• Pyruvate is converted to ethanol

to regenerate NAD+• Ethanol is a potentially toxic

waste product • Yeast carry out alcoholic

fermentation when oxygen deprived

Lactate Fermentation

• Bacteria and some fungi carry out lactate fermentation

• Pyruvate is converted to lactate to regenerate NAD+

• Strenuous exercise in mammals results in lactate fermentation as well

http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/index.html