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 Spectra

OE 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.