Flow of energy in biological systems – Organisms transform energy and fuel metabolism
Flow of energy in biological systems – Photosynthetic reaction is the reverse of cellular respiration
6 CO + 6 H O C H O + 6 O
2 2 6 12 6 2
(+ light energy) (+ ATP + release of heat)
Other carbohydrates,fats, and proteins are also used as fuel for cellular respiration, but glucose is
starting point for glycolysis
Key Concepts - Respiration
• Endergonic reactions (requiring energy) are needed for cellular metabolism
• They are paired with exergonic reactions (releasing energy) involving ATP
• Cellular respiration produces ATP from moleculeswith high potential energy – e.g. glucose
• Glucose processing has four components:
(3) Krebs cycle (Citric acid cycle or Tricarboxylic acid cycle)
(4) Electron transport coupled with oxidative phosphorylation
• Fermentation– alternativepathways
○ Glycolysiscontinues when lack of an electron acceptor shuts down electron transport
• Respiration and fermentationare carefully regulated
ATP is used in organisms to drive endergonic reactions, because it is high in potential! Hydrolysis of bond between two outermostphosphate groups
-> formation of ADP and Pi (H P2 ) 4n a highly exergonic reaction
-> 7.3 kcal of energy released mole of ATP
-> in cells this energy is not lost as heat! Instead:
Transfer of released phosphate group to a protein -> Phosphorylation
-> usually causes change in protein's shape
Phosphorylation changes shape and activity of proteins
How does ATP drive endergonic reactions?
Coupling between phosphorylationand endergonic reactions!
• Protein phosphorylation- exergonic phosphorylation reaction paired with endergonic reaction
-> energetic coupling
• In cells, endergonic reactions becomeexergonic when substrate or enzymes involved are
-> exergonic phosphorylation reaction
• Phosphorylation(adding negative charge) drives endergonic reactions
• Adding a negatively charged phosphate group to a protein changes the protein’s structure
-> Activation of enzymes or reactants Energetic coupling provides the energy to phosphorylate enzymes and reactants when ATP loses a
How is ATP generated through cellular respiration?
Where does the energy come from, to generate ATP from ADP and Pi?
-> Breakdown of glucose in series of redox reactions
What Is a Redox Reaction?
• Reduction–oxidationreactions (redox reactions) in cellular respiration
○ Chemical reactions involving loss or gain of an electron
○ Release of energy stored in organic molecules
○ Released energy is ultimatelyused to synthesize ATP
• Oxidation - loss of electrons
• Reduction – gain of electrons
• Oxidation events are always coupled with a reduction
○ An electron donor always paired with an electron acceptor.
• During a redox reaction, electrons can be transferred completelyfrom one atom to another, or
they can shift their position in covalent bonds.
Photosynthesis – an example for redox reactions and the gain & loss of electrons
An Overview of Cellular Respiration
• Glucose (animals) or sucrose (plants) are key intermediaryin cell metabolism
• Cells use glucose to buil