This document contains a lecture on oxidation-reduction (redox) reactions in living organisms. It discusses how: 1. Redox reactions involve the transfer of electrons, with oxidation being the loss of electrons and reduction being the gain of electrons. 2. Important redox reactions in biological processes are photosynthesis and cellular respiration. Photosynthesis converts sunlight into chemical energy by using a redox reaction, while cellular respiration releases energy through a combustion reaction. 3. ATP generation during cellular respiration occurs through substrate-level phosphorylation and oxidative phosphorylation. Oxidative phosphorylation uses an electron transport chain to produce ATP indirectly as electrons from glucose are transferred to lower energy states.

1. Ms. Uzma Irfan
Lecturer
The Department of Botany
The Women University Multan
Email: uzma.6370@wum.edu.pk
PLANT BIOCHEMISTRY
Lecture 2

2. OXIDATION-REDUCTION REACTION IN LIVING
ORGANISMS
PLANT BIOCHEMISTRY
BOT-510

3. CONTENT
Oxidation-Reduction Reaction in
Living Organism
Photosynthesis → Redox
process
Cellular Respiration → Redox
process

4. OXIDATION-REDUCTION REACTION IN LIVING
ORGANISMS
• Also known as Redox Reaction
• Involves the transfer of electrons
Oxidation is losing electron
Reduction is gaining electron
• LEO GER: loss of electron(Oxidation) & gain of electron(Reduction)

5. REDOX REACTIONS IN LIVING ORGANISMS
• Oxidation and reduction reactions in biological processes are
Cellular respiration and
Photosynthesis

6. PHOTOSYNTHESIS AS REDOX PROCESS
• Green plants carry out the redox
reaction
• Converts sunlight into chemical
energy
• Makes possible almost all life on
earth.

7. Glucose gives off energy as it is oxidized
CELLULAR RESPIRATION AS REDOX PROCESS
• This reaction, is simply a combustion reaction
• As gasoline in an engine
• Process is broken down into many smaller steps
• Energy of glucose is released in small bursts

8. THE GENERATION OF ATP
• Generated either by
Substrate level phosphorylation
Oxidative phosphorylation

9. THE GENERATION OF ATP
• Substrate level phosphorylation
• In these steps, a phosphate group is transferred from a pathway intermediate
straight to ADP, a process known as substrate-level phosphorylation.
C-C-C~P + ADP→C-C-C + ATP
• Two such phosphorylation occurs in Glycolysis &
• One in the Krebs cycle

10. THE GENERATION OF ATP
• Oxidative phosphorylation
• Many more steps
• Produce ATP in an indirect way.
• Electrons from glucose are transferred to electron carriers in electron transport
chain.
• As electrons move, go from a higher to a lower energy level
• Ultimately passed to oxygen (forming water).
• Energy released, powers production of ATP by ATP synthetase.

12. • Cellular respiration involves
 Reactions in which electrons are passed from one molecule to another.
 Known as oxidation-reduction reactions (or redox reactions),
• They play a central role in the metabolism of a cell.

13. ELECTRON CARRIERS
• Sometimes called Electron shuttles
• Organic molecules
• Readily cycle between oxidized and reduced forms
• Used to transport electrons during metabolic reactions.
Play particularly important roles during cellular respiration

14. ELECTRON CARRIERS
There are two electron carriers
• NAD+ (nicotinamide adenine dinucleotide) and
• FAD (flavin adenine dinucleotide).

15. REDOX REACTIONS WITH CARBON CONTAINING
MOLECULES
• Fundamentally about the transfer of electrons.
• In the context of biology,
“Gain or loss of H and O atoms as a proxy for the transfer of electrons.”
• As a general rule of thumb,
gains H atoms or loses O atoms →→→ Reduced (gained electrons)
loses H atoms or gains O atoms →→→ Oxidized (lost electrons)
• For example, let’s go back to the reaction for glucose breakdown,

17. IN CELLS UNDERSTAND THE ROLE OF MOVEMENT OF ELECTRONS
PLAYS IN ENERGY EXCHANGES
• In redox reactions,
• energy is released when an electron loses potential energy(PE) as a result of the
transfer.
• When electrons are associated with
less electronegative atoms (such as C or H) →→→ have more PE
more electronegative atom (such as O) →→→ have less PE

18. • Redox reaction that moves
Electrons or electron density from a less electronegative atom
A more electronegative atom
Will be spontaneous and release energy.

19. • The energy that's released, captured and used to do work.
• In cellular respiration
• Electrons from glucose move, passing to lower and lower energy states
• Releasing energy at each step.
• The goal of cellular respiration is to capture this energy in the form of ATP.

20. ELECTRONS & ENERGY

21. WHAT'S THE POINT OFALL THIS REDOX?