Bioenergetics Lecture 5 summary
• Susan.Kaminskyj@usask.ca
• Last time –integrating catabolic metabolism, review catabolism
• This time
– similarities and differences between cellular respiration and photosynthesis
– chlorophyll, photosystems II and I (in that order)
• But first….!

Electron transport chain pumps H + , making a gradient
ATP synthase uses the H + gradient to generate ATP
Higher H + concentration = lower pH
Intermembrane space
Potential energy of falling water used to grind grain
Potential energy of
‘falling’ H + used to generate ATP
Lower H + concentration = higher pH
Mitochondrial matrix

ATP synthase uses the H + gradient to generate ATP

Cellular Respiration

A series of redox reactions ….
RESPIRATION
PHOTOSYNTHESIS
PHOTOSYNTHESIS
RESPIRATION

Respiration vs photosynthesis
• Mitochondria
– All aerobic eukaryotes
• Oxidation of CHO to CO
2
• Generation of NADH and
FADH
2
 ATP synthesis
• Chloroplasts
– Plants, algae
• Energy harvest from sunlight
• Generation of NADPH
 Reduction of CO
2 to CHO
CHO = carbohydrate

Photosynthesis is an endothermic redox process
Energy source?
Useful byproducts?
Sunlight
Glucose and O
2

Red and Blue light are absorbed from the incident
(white) light, leaving Green to be reflected or transmitted

Photosynthesis produces oxygen
Are all wavelengths photosynthetically active?
Spirogyra
Photosynthetic
Active spectrum

First, light energy must be captured
Illuminated chlorophyll fluoresces
(gives off light) if captured light energy is not transferred to another acceptor

Capture is not enough!
In a leaf, the reaction centre transfers the captured energy to a relatively stable intermediate
Isolated chlorophyll fluoresces if newly captured energy is not transferred chemical

The reaction centre is the heart of the photosystem
Energy transfer between pigment molecules to a special central pair of chlorophylls
(reaction centre) and thence to the primary electron acceptors

Two parts to the light reaction

Chemiosmosis can make ATP

Two parts to the light reaction phaeophytin ferredoxin

Source and fate of carbon and oxygen in carbohydrates formed by photosynthesis

Photosystem II makes ATP

Photosystem I makes NADPH

NADH vs NADPH
• NADH  catabolism
• NADPH  anabolism
(P  p hotosynthesis)
• For each, the reduced form stores ~ 3 times more energy than ATP