2/16/15

1

Ch 10: Photosynthesis

photoautotrophs photoheterotrophs

& green sulfur bacteria

Halobacterium (Archaea)

green & purple non-sulfur bacteria

Photosynthesis variations Why so many kinds?

bacteriochlorophylls bacteriorhodopsin chlorophyll a

Halobacterium: proton pump + ATP synthase

south San Francisco Bay

Owen’s Lake (from Wikipedia) from Wikipedia

2/16/15

2

Algae

Group PS Pigments

Euglenoids chl a & b, carotenoids

Dinoflagellates chl a & c (usually), carotenoids

Diatoms chl a & c, carotenoids

Xanthophytes chl a & c, carotenoids

Chrysophytes chl a & c, carotenoids

Coccolithophorids chl a & c, carotenoids

Browns chl a & c, carotenoids

Reds chl a, phycobilins, carotenoids

Greens chl a & b, carotenoids

Photosynthetic structures in a land plant

2 sets of reactions: Photo synthesis

2/16/15

3

“Magic” molecule

Why leaves are green

How did we figure that out? spectrophotometry?

(1883)

2/16/15

4

Why is chlorophyll a special?

can travel to an electron acceptor OR

Reaction center

Photosystems contain - light harvesting complexes - proteins - antenna pigments - reaction center

Accessory pigments: other non-reaction center chlorophylls carotenoids

phycobilins

2/16/15

5

Light dependent reactions of photosynthesis: a) Non-cyclic photophosphorylation

chan

ge in

free

ene

rgy

In and around the thylakoid disk: photophosphorylation

Light dependent reactions of photosynthesis: b) Cyclic photophosphorylation

but why?

2/16/15

6

Melvin Calvin

Light independent reactions of photosynthesis: Calvin-Benson cycle (C3 cycle)

RuBP carboxylase/oxidase = Rubsico in plants is a complex (L8S8) of: * 8 large catalytic subunits (L, 477 amino acid residues) * 8 small subunits (S, 123 amino acid residues). (Some bacteria contain only the large subunit.) At right are 2 views of spinach RuBisCO (RuBP Carboxylase), with large subunits colored blue or cyan, and small subunits colored red.

Large subunits within RuBisCO are arranged as antiparallel dimers, with the N-terminal domain of one monomer adjacent to the C-terminal domain of the other monomer. Each active site is at an interface between monomers within an L2 dimer. The substrate binding site is at the mouth of an ab-barrel domain of the large subunit. Most active site residues are polar, including some charged amino acids (e.g., Thr, Asn, Glu, Lys).

Light independent reactions of photosynthesis: Calvin-Benson cycle (C3 cycle)

2/16/15

7

1 problem

Photorespiration: Rubisco makes a mistake

from: Wikipedia

1 solution:

C4 photosynthesis: don’t allow Rubisco to see much O2

Kranz anatomy

Rubisco

(low O2)

Crassula

different threat: severe dehydration -> CAM (crassulacean metabolism) photosynthesis

2/16/15

8

So what did we just talk about doing (free energy-wise)?