Chapter 19
Part 3
Photophosphorylation
Learning Goals: To Know
1. How energy of sunlight creates charge separation in the
photosynthetic reaction complex and exciton transfer.
2. How electron transport is accompanied by the directional
transport of protons across the membrane against their
concentration gradient
3. Similarities and differences between plant-algal
photosystems and bacterial photosystems.
4. How the electrochemical proton gradient drives synthesis
of ATP by coupling the flow of protons via ATP synthase to
conformational changes that favor formation of ATP in the
active site
5. Roles of rhodopsins.
Primary Production – Solar Energy Conversion
Chloroplasts
How do Photosynthetic Bacteria Fit in Here?
Hill Reaction (driven by light) in Photophosphorylation
2 H2 O + 2 A
 2 AH2 + O2
“A” in Biological Systems = NADP+ so the Hill
Reaction is:
2 H2O + 2 NADP+  2 NADPH + 2H+ + O2
What Robert Hill in 1937 Actually Measured Was:
The reduction of DCIP: going from blue to colorless.
Electromagnetic Spectrum
What is an Einstein?
Light Energy
Planck-Einstein Equation:
E=hν
E = energy of a photon
h = Planck’s Constant = 6.6 x 10-34 J.s
v = vibration frequency ( of the wavelength of light; vibrational
frequency increases with a decrease in
wavelength )
In the text,
E = hc/λ
So that one red photon
c/λ = v
so red light, λ = 700 nm, c = 3x108m/s
E = 2.83 x 10-19 J
For an Einstein (a mole of photons) E = 168 kJ/einstein
Chlorophyll a
What is with the PINK ???
Phycobilins
Carotenoids
Photopigment Absorption Spectrum
Chlorophyll Types
Noon, Nov 18th: Surface
Sun Light Spectra
OE Pond
Where is the Visible and
Infra-red light ? Which one
gets to the bottom?
Noon, Nov 18th: Bottom
The y-axis is in
units of
(einsteins/s)/m2 at
each wavelength.
Light Harvesting Complexes Have Many Chlorophylls
Phycobilisome of Cyanobacteria
Engleman Experiment (1882): Action Spectrum
Light Harvesting – Energy Transfer to Reaction Center
Solid State Photo-electron
Transfer
Two Bacterial Photosystems
EOC Problem 28: Role of H2S in bacterial photosynthesis
Purple Bacterial Reaction Center
The Z Scheme is Both Linear and Circular
EOC Problem
30 on electron
flow between
PS-I and PS-II.
Photosystem II
Photosystem I
Trimer and Stripped Monomer Structure of
PS I
Electron and Proton Flow: Cyt-b6f Complex
Cytochrome b6f Complex Pumps Protons
Localization of PS1 and PS2 in Thylakoid Membrane
Water Splitting Protein Utilizes all 5 Redox States of Mn
Summary
EOC Problem 41 on the
Function of cyclic
photophosphorylation.
Comparison of Mitochondrion, Chloroplast, Bacteria
Cytochrome b6f Complex Functions in
Photophosphorylation AND Respiratory E-transport
In Cyanobacteria
Bacterial Rhodopsin – Becoming Ubiquitous
Rhodopsin Proton Transfer: Cis -Trans Conformational
Change
Rhodopsins Are Becoming Recognized as Common
There are 3 Classes of Rhodopsins:
1. Proton Pumping (previous example) – Halophilic
Archaea.
2. Signal Transduction – Vision and Light/Dark
Adaptions.
3. Chloride Pumping.
They occur in Archaea, Bacteria and Eukarya - All Domains
of Life
To Know and Do Before Class
• The energy of sunlight creates charge separation in the
photosynthetic reaction complex and exciton transfer.
• Stepwise electron transport is accompanied by the
directional transport of protons across the membrane
against their concentration gradient
• Similarities and differences between plant-algal
photosystems and bacterial photosystems.
• The energy in the electrochemical proton gradient drives
synthesis of ATP by coupling the flow of protons via ATP
synthase to conformational changes that favor formation
of ATP in the active site
• Roles of rhodopsins.
• EOC Problems: 28, 30, 31, 35, 41.