Photosynthetis organisms and process of photosynthesis.ppt

Photosynthesis

1. Photosynthetic organisms
•Anoxygenic Photosynthesis
–Green and purple (sulfur and non-sulfur)
bacteria and heliobacteria
•Oxygenic Photosynthesis
• Cyanobacteria

2. Pigments
•Light harvesting pigments
–Bacteriochlorophyll (bchl) for
anoxygenic photosynthesis
–Chlorophyll for oxygenic
photosynthesis
–Different varieties that can
absorb light at different
wavelengths
Harness energy from light to excite electrons to higher energy
states (more reducing, more negative E
0
) – these high energy
electrons go through the electron transport chains to ultimately
produce energetic molecules like ATP and NADPH to drive
biochemical reactions in the cell

3. Pigment
Chl a Chl b BChl a BChl bBChl cBChl dBChl e
Color in graph
above
black red magentaorange cyan blue green
Absorption
maxima
(nm)
430, 663463, 648364, 770373, 795434,666427,655469, 654
Other pigments can harvest light energy at wavelengths an organism’s chlorophyll
cannot – includes caratenoids, phycobilins (blue), and phycoerythrin (red)

5. Q cycle
•Ubiquinone (Q) pool is critical to H
+

shuttling to maintain the pmf and drive
phosphorylation to produce ATP
Quinone (Q) is reduced
with an electron through
cytochrome bc1 to form
hydroquinone (QH
2) –
QH
2
is then oxidized by
another site on
cytochrome bc1 back to Q
– this shuttles H
+
across
the membrane, the H
+

goes through ATPase
back into the cell,
generating ATP
http://www.geocities.com/awjmuller/anims_images/bacterialPSfast.gif for animation...

6. Anoxygenic photosynthesis

7. Anoxygenic photosynthetic organisms
•Purple and green bacteria utilize bchl and H
2S, S
8,
S
2O
3
2-
, H
2, Fe
2+
, and organics as electron donor
–Many can deposit elemental sulfur intracellularly (and
sometime outside the cell (epicellularly) to store that when H
2S
is unavailable
–The term non-sulfur does not necessarily mean they can’t use
sulfur - they are generally adapted to environments with less
sulfur
•Heliobacteria – Nitrogen-fixing,
heterotrophic organisms found in soils
and rice paddies
Beggiatoa spp.

8. Oxygenic Photosynthesis
Water-oxidizing complex is key –
Mn4Ca-complex that oxidizes H
2
O
to O
2
in 4 steps (S
0
through S
4
)
Chlorphyll a (P680) is very oxidized (E
0
=+1.1V),
enough to oxidize H
2
O. BUT e- excitation takes it to
E
0
=-0.7V, not enough to reduce NADP+ to NADPH.
Thus a need for 2 photosystems….

9. Non-cyclic phosphorylation
•Coupled photosystems
linked by plastocyanin
(pc), which takes the e-
excited by P680, after it
goes through the Q pool,
and puts it into a similar
chlorophyll a (P700) which
is excited by a photon to a
very reduced potential
(-1.3V) that can reduce
NADP+ to NADPH
•If there is enough NADPH,
PS I can act independently
and function for cyclic
phosphorylation

10. Transfer Of Electrons &ATP synthesis