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

Fo in inner

mem

brane

F1 in

matrixLower H+ concentration = higher pH

Mitochondrial matrix

Higher H+ concentration = lower pH

Intermembrane space

ATP synthase uses the H+ gradient to generate ATP

Potential energy of falling waterused to grind grain

Potential energy of ‘falling’ H+ used to generate ATP

ATP synthase uses the H+ gradient to generate ATP

Cellular Respiration

A series of redox reactions ….

PHOTOSYNTHESIS

RESPIRATION

RESPIRATION

PHOTOSYNTHESIS

Respiration vs photosynthesis

• Mitochondria– All aerobic eukaryotes

• Oxidation of CHO to CO2

• Generation of NADH and FADH2

ATP synthesis

• Chloroplasts– Plants, algae

• Energy harvest from sunlight• Generation of NADPH

Reduction of CO2 to CHO

Note NADH (respiration) vs NADPH (photosynthesis)P photosynthesis

CHO = carbohydrate

Photosynthesis is an endothermic redox process

Energy source?

Useful byproducts? Sunlight

Glucose and O2

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

Photosynthesis produces oxygen

Are all wavelengths photosynthetically active?

Spirogyra

PhotosyntheticActive 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!

Isolated chlorophyll fluoresces if newly captured energy is not transferred

In a leaf, the reaction centre transfers the captured energy to a relatively stable intermediate 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 reactionphaeophytin

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 photosynthesis)

• For each, the reduced form stores ~ 3 times more energy than ATP