Transcript Powerpoint 25 - Photosynthesis

Central metabolism

Where do the molecules we eat come from?
polysaccharides
glucose
glycolysis
fermentation
organic
wastes
ATP
proteins
lipids
acetyl
CoA
amino acids
TCA
cycle
ATP
ATP
ATP
oxidative
phosphorylation
CO2
ATP
ATP
Photosynthesis

Ultimate source of carbon and energy for all living things
Halobacterium: Simplest photosynthesis

Bacteriorhodopsin uses light energy to pump protons
light
H+
outside
cytoplasm
H+ H+
H+
H+
H+
H+
H+
H+
bacteriorhodopsin
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
ATP
synthase
ADP
ATP
Plants have been doing this for a while…
Plant photosynthesis overview

Light powers ATP synthesis

CO2 + ATP used to synthesize glucose
CO2
light
energy
glucose
ATP
Reactions of photosynthesis

Light-dependent: capture energy as ATP and NADPH

Light-independent: CO2 → glucose (“fix” carbon)
CO2
light
energy
glucose
ATP
6 CO2 + 6 H2O + Light Energy  C6H12O6 + 6 O2
The chloroplast

Light-dependent reactions in thylakoid membrane

Light-independent reactions in stroma
o.m.
i.m.
stroma
t.m.
thylakoid
thylakoid
space
granum
Light-dependent reactions
Capture light energy as ATP and NADPH

Occur in thylakoid membrane
e-
free
energy
(G)
photosystem II
light
light
ADP
ATP
e-
e-
photosystem I

NADP
NADPH
e-
Chlorophyll

Light-harvesting pigment in thylakoid membrane

Lipid-like structure with large carbon ring

Absorbs blue and red wavelengths of light (reflects back green)
Photosystem II

“Satellite dish” of chlorophyll in membrane

Light-gathering “antenna” molecules

Pass energy to “reaction center” or (“special pair”) chlorophyll
light
Photosystem II

Reaction center chlorophyll oxidizes H2O → O2

Using light energy, energizes e–

Transfers e– to electron transport chain
e-
light
e–
H2O
O2
electron
carrier
photosystem II
light
e-
Photosystem II

Electron transport

Cytochrome oxidase complex pumps H+ into thylakoid space

Electrons transferred to Photosystem I
stroma
H2O
photosystem II
H+
cytochrome
oxidase
complex
O2
photosystem I
e–
thylakoid space
H+
H+
H+
H+
H+
H+
Photosystem II

H+ gradient used to synthesize ATP
ATP
stroma
H2O
photosystem II
O2
ADP
ATP
synthase
H+
cytochrome
oxidase
complex
H+
e–
thylakoid space
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
Photosystem I
Second chlorophyll complex

Re-energizes “used” electron
e-
free
energy
(G)
photosystem II
light
light
ADP
ATP
e-
e-
photosystem I

NADP
NADPH
e-
Photosystem I

Electron transport

Electron transferred to NADP+ → NADPH

Electrons transferred to Photosystem I
stroma
H2O
photosystem II
H+
cytochrome
oxidase
complex
O2
photosystem I
e–
thylakoid space
H+
H+
H+
H+
H+
H+
NADP+ NADPH
Light-dependent reactions
Capture light energy as ATP and NADPH

Why does the plant want NADPH?
e-
free
energy
(G)
photosystem II
light
light
ADP
ATP
e-
e-
photosystem I

NADP
NADPH
e-
Light-independent (“dark”) reactions
ATP NADPH
CO2

glucose
Why does the plant want to make glucose?
Light-independent (“dark”) reactions

CO2 reduced to make glucose

Occurs in stroma

Calvin cycle
CO2
ATP
NADPH
3C carbohydrate
glucose
Light-independent (“dark”) reactions

Key reaction catalyzed by RuBisCo
 Ribulose bisphosphate carboxylase
 Most abundant enzyme!
CO2
RuBisCo
5C
6C
3C
3C
Photosynthesis
CO2
light
ADP ATP NADP NADPH
H+
H2O
O2
glucose
Which organelle would not be found in a plant cell?
a.
Chloroplast
b.
ER
c.
Mitochondrion
d.
Golgi
e.
Nucleus
f.
none of the above
light
glucose
ATP
Respiration & photosynthesis: similarities

Harvest energy in usable forms

Electron transport

Multi-step biochemical pathway

Oxidation-reduction

O2