6-1 Energy for Life
Where does it come from?
Oil, coal, gas
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
ATP and ADP
Energy in released in cell is not used directly
Its 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
Cant 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
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
Carbon dioxide production causes bread to rise
Note: fermentation is believed to be the most primitive form of cellular 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
Coenzyme, called coenzyme A ( CoA )
Forms acetyl CoA
Figure 6-6, p. 115
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
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
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
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
Back to: Notebook