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Cellular Respiration

Chapter 6

6-1 Energy for Life


Where does it come from?

Oil, coal, gas

Chemical process

Physical and mechanical work

Cells need continuous supply of energy to stay alive.

Energy from Food

Chemical energy stored

Carbohydrates heat maintains body temperature

Carry out life functions

Cellular respiration – energy releasing process


Energy in released in cell is not used directly

It’s packaged in a compound

ATP – adenosine triphosphate

Figure 6-2, p. 109 – structure of ATP

1 molecule of adenine joined to 1 molecule of ribose = adenosine

3 phosphate groups

Bond linking last phosphate group most important

Wavy line means large amount of energy

High - energy bond

Phosphorylation – transfer of energy in cells

Figure 6.3, p. 109 ( handout diagram )

Remove the third phosphate from ATP, becomes ADP

Adenosine diphosphate – has less energy

The Source of Energy for ATP

Attaching a third phosphate to ADP.

Changes ADP to ATP.

Glucose – cells energy

Found in complex form


Can’t use all the energy at once

Oxidation – Reduction Reactions

Steps to follow for energy to be released from glucose to produce ATP

Oxidation – lose electrons

Reduction – gain electrons

Gain and lose of hydrogen atoms

Transfer of energy

Key role in cellular respiration

Electron Acceptors

Glucose broken down in several steps

Biochemical pathway – sequence of chemical reactions

NAD+ and FAD accept a pair of high energy electrons and a proton ( H + ), undergoes a reduction

NAD+ + 2e- + 2 H + ΰ NADH

FAD + 2e- + 2 H + ΰ FADH 2

These gain energy and it is temporary

6.2 Anaerobic Respiration

Types of Respiration

Aerobic – with free Oxygen

Glucose completely oxidized to carbon dioxide and water

Maximum amount of energy removed from glucose

Anaerobic – without Oxygen

Yeast and many forms of bacteria

Receives little of the chemical energy in glucose

Splitting of Glucose

Glycolysis – breakdown of glucose molecule into 2 3 carbon pyruvic acid molecules

Figure 6-4, p. 113

Fermentation – when glycolysis is followed by the conversion of pyruvic acid to some end product with no further release of energy

Bread making

Carbon dioxide production causes bread to rise

Note: fermentation is believed to be the most primitive form of cellular respiration.

Aerobic Respiration

The Importance of Oxygen

Oxygen is not needed for each stage of the aerobic process.

Oxygen is only required as the final hydrogen acceptor

Pyruvic Acid Breakdown

Pairs of electrons from NADH

No further energy is released

Aerobic, further breakdown and energy release

Some energy from NADH during glycolysis


Inner membrane

Coenzyme, called coenzyme A ( CoA )

Forms acetyl CoA

Figure 6-6, p. 115

Krebs Cycle

Also called the Citric-acid cycle, after citric acid, the first compound formed in the series of reactions.

Series of chemical reactions that begin with the acetyl CoA formed from pyruvic acid is called the Krebs Cycle.

Discoverer, Sir Hans Krebs of Oxford University in England

Repeating cycle

Figure 6-7, p. 116

Pyruvic acid from glycolysis reacts to form acetyl CoA, which then enters the Krebs cycle. For every turn of the cycle, 2 molecules of CO2, 3 molecules of NADH, 1 molecule of FADH2, and 1 ATP molecule are Produced.

Electron Transport Chain

The electron transport chain is a series of electron carriers on the inner membrane of the mitochondrion. NADH and FADH2 deliver electrons to the electron transport chain. As the electrons pass from one electron carrier to the next, they release energy, and ATP is formed. At the end, the electrons, hydrogen ions, and free oxygen combine to form water molecules.

Electron transport chain is not a structure but rather locations within the mitochondria that have specific enzymes.

Net Reactions of Aerobic Respiration

Net results of all steps of aerobic respiration


C6H12O6 + 6 O2 ΰ 6 CO2 + 6 H2O + Energy ( 36 ATP )

Should be written

C6H12O6 + 6 H2O + 6 O2 ΰ 6 CO2 + 12 H2O + Energy ( 36 ATP )

Efficiency of Cellular Respiration

Figure 6-9, p.118

45% of the total energy obtainable from the oxidation of glucose is stored as ATP molecules after aerobic respiration.

Note: Under normal conditions, ATP is used by an organism within seconds of its production.

Muscle Fatigue and Oxygen Debt

Rely on aerobic respiration to meet energy needs

Can function for a short period of time without oxygen, but can use the energy from glycolysis alone.

Prolonged activity may use oxygen faster than than supplied.

Krebs Cycle stops

Build up of lactic acid

Oxygen debt

Note: Most of the lactic acid produced in muscle tissue is converted by the liver into pyruvic acid

Respiration of Fats and Proteins

Extraction of energy from other food substances

Converted into compounds

Figure 6-11, p. 119

Fats and twice the amount of ATP produced

Weight gain

Twice as active to lose weight

Proteins not preferred as a energy source for the cell

Yields about the same amount of energy as a gram of carbohydrates

The Evolution of Cellular Respiration

Biologists believe glycolysis was first biochemical process to evolve.

Primitive planet with prokaryotic cells

More efficient pathways


Step by step process building on earlier processes

Cellular respiration

The End

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