Download Ch 10 Slides - people.iup.edu

Overview: The Process That Feeds the Biosphere
• Photosynthesis is the process that converts
solar energy into chemical energy
• Directly or indirectly, photosynthesis nourishes
almost the entire living world
Autotrophs
• Autotrophs sustain themselves without eating
anything derived from other organisms
• Autotrophs are the producers of the biosphere,
producing organic molecules from CO2 and
other inorganic molecules
• Almost all plants are photoautotrophs, using
the energy of sunlight to make organic
molecules from H2O and CO2
Photosynthesis
occurs in plants,
algae, certain
other protists, and
some prokaryotes
(a) Plants
(c) Unicellular protist
10 µm
(e) Purple sulfur
bacteria
(b) Multicellular alga
(d) Cyanobacteria
40 µm
1.5 µm
Heterotrophs
• Heterotrophs obtain their organic material
from other organisms
• Heterotrophs are the consumers of the
biosphere
• Almost all heterotrophs, including humans,
depend on photoautotrophs for food and O2
The Two Stages of Photosynthesis: A Preview
• Photosynthesis consists of the light reactions
(the photo part) and Calvin cycle (the synthesis
part)
• The “light” reactions are in the thylakoids
• The Calvin cycle is in the stroma
Chloroplast
Outer
membrane
Thylakoid
Stroma
Granum
Thylakoid
space
Intermembrane
space
Inner
membrane
1 µm
• The “light” reactions overview
– Capture light energy using chlorophyll
– Split H2O to electrons, protons and oxygen
– Release O2
– Reduce NADP+ to NADPH
– Generate ATP from ADP by
photophosphorylation
• The Calvin cycle overview
- begins with carbon fixation, incorporating CO2
into organic molecules
- forms sugars from these organic molecules,
using ATP and NADPH (from light reactions)
H2O
Light
NADP+
ADP
+ P
i
Light
Reactions
Chloroplast
Overview of Photosynthesis 1
H2O
Light
NADP+
ADP
+ P
i
Light
Reactions
ATP
NADPH
Chloroplast
O2
Overview of Photosynthesis 2
CO2
H2O
Light
NADP+
ADP
+ P
i
Light
Reactions
Calvin
Cycle
ATP
NADPH
Chloroplast
O2
Overview of Photosynthesis 3
CO2
H2O
Light
NADP+
ADP
+ P
i
Light
Reactions
Calvin
Cycle
ATP
NADPH
Chloroplast
Overview of
Photosynthesis 4
O2
[CH2O]
(sugar)
Chlorophyll is the light-capturing substance
Surrounded by
other pigment
molecules,
enzymes and
electron carriers
A “photosystem”
• Anchored to
thylakoid
membranes by
proteins
Illustration of important properties of chlorophyll
Energy of electron
e–
Excited
state
Heat
Photon
(fluorescence)
Photon
Chlorophyll
molecule
Ground
state
(a) Excitation of isolated chlorophyll molecule
(b) Fluorescence
If illuminated, a solution of chlorophyll will fluoresce, giving off
light and heat
Photosystem
STROMA
Light-harvesting Reaction-center
complex
complexes
Primary
electron
acceptor
Thylakoid membrane
Photosynthetic
Photon
Energy
Capture
e–
Transfer
of energy
Special pair of
chlorophyll a
molecules
Pigments-chlorophyll
and accessory
THYLAKOID SPACE
(INTERIOR OF THYLAKOID)
“Z-Diagram” of photosynthesis
4
Primary
acceptor
2
H+
+
1/ O
2
2
H2O
e–
2
Primary
acceptor
e–
Pq
Cytochrome
complex
7
Fd
e–
e–
8
NADP+
reductase
3
NADPH
Pc
e–
e–
P700
5
P680
Light
1 Light
6
ATP
Pigment
molecules
Photosystem II
(PS II)
NADP+
+ H+
Photosystem I
(PS I)
This illustrates “non-cyclic” electron flowelectrons enter with water and leave with NADPH
Primary
acceptor
Primary
acceptor
Fd
Fd
Pq
NADP+
reductase
Cytochrome
complex
NADP+
+ H+
NADPH
Pc
Photosystem I
Photosystem II
ATP
Cyclic electron flow uses
only photosystem I and
produces ATP, but not NADPH
• “Light” reactions of PSI and PSII generate ATP
and “reducing power” in the form of NADPH
• Reducing power allows the conversion of
carbon dioxide to carbohydrate
• CO2 to CH2O requires NADPH reducing power
Input 3
Carbon fixation
conversion of carbon
dioxide to carbohydrate
(Entering one
at a time)
CO2
Phase 1: Carbon fixation
Rubisco
3 P
Short-lived
intermediate
P
6
P
3-Phosphoglycerate
3P
P
Ribulose bisphosphate
(RuBP)
6
ATP
6 ADP
Calvin
Cycle
3 ADP
3
ATP
6 P
P
1,3-Bisphosphoglycerate
6 NADPH
Phase 3:
Regeneration of
the CO2 acceptor
(RuBP)
6 NADP+
6 Pi
P
5
G3P
Rubisco is
the key
enzyme of
the cycle
6
P
Glyceraldehyde-3-phosphate
(G3P)
1
Output
P
G3P
(a sugar)
Glucose and
other organic
compounds
Phase 2:
Reduction
Plants that
use this cycle
exclusively are
C3 plants
• Dehydration is a problem for plants, sometimes
requiring trade-offs with other metabolic
processes, especially photosynthesis
• Plants have evolved two alternate types of
carbon fixation
• C4 and Crassulean Acid Metabolism (CAM)
fixation
H2O
CO2
Light
NADP+
ADP
+ P
i
Light
Reactions:
Photosystem II
Electron transport chain
Photosystem I
Electron transport chain
RuBP
ATP
G3P
Starch
(storage)
NADPH
Chloroplast
3-Phosphoglycerate
Calvin
Cycle
C3 Photosynthesis:
a review
O2
Sucrose (export)
Note Card Questions
1) What is the “reducing power” of NADPH and
how does it link the light reactions with the
Calvin Cycle?
2) Why are 2 light absorbance events (2
photons) required by oxygenic
photosynthesis?