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 H2O + 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 = h ν

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 c/λ = v so red light, λ = 700 nm, c = 3x108m/s

So that one red photon 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

Sun Light SpectraOE Pond

Where is the Visible and Infra-red light ? Which one gets to the bottom?

Noon, Nov 18th: Surface

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.