Central metabolism

glucose

oxidativephosphorylation

TCAcycle

glycolysis

fermentation

organicwastes

CO2

ATP

ATP

ATP

ATPATP

ATP

acetylCoA

polysaccharides

lipids

amino acids

proteins

Where do the molecules we eat come from?

Photosynthesis Ultimate source of carbon and energy for all living things

Halobacterium: Simplest photosynthesis Bacteriorhodopsin uses light energy to pump protons

H+

outside

cytoplasm

H+

H+

H+

H+

H+H+ H+ H+ H+

H+H+ H+

H+H+ H+

ATPsynthase

H+ H+ H+

ADPATP

bacteriorhodopsin

light

Plants have been doing this for a while…

Plant photosynthesis overview Light powers ATP synthesis CO2 + ATP used to synthesize glucose

lightenergy

ATP

CO2

glucose

Reactions of photosynthesis Light-dependent: capture energy as ATP and NADPH Light-independent: CO2 → glucose (“fix” carbon)

lightenergy

ATP

CO2

glucose

6 CO2 + 6 H2O + Light Energy C6H12O6 + 6 O2

The chloroplast Light-dependent reactions in thylakoid membrane Light-independent reactions in stroma

thylakoid

thylakoidspace

t.m.

i.m.o.m.

granum

stroma

Light-dependent reactions Capture light energy as ATP and NADPH Occur in thylakoid membrane

freeenergy

(G)

e-

e-e-

e-

ph

oto

sys

tem

II

ph

oto

sys

tem

I

lightlight

ATPADP NADPH

NADP

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

light

H2OO2

e– electroncarrier

e-

e-

ph

oto

sys

tem

II

light

Electron transport Cytochrome oxidase complex pumps H+ into thylakoid space Electrons transferred to Photosystem I

Photosystem II

stroma

thylakoid space

H2O O2

H+

H+

e–

H+

H+

H+H+

H+

cytochromeoxidasecomplexphotosystem II photosystem I

H+ gradient used to synthesize ATP

Photosystem II

stroma

thylakoid space

H2O O2

H+

H+

e–

H+

H+

H+H+

H+

cytochromeoxidasecomplexphotosystem II

H+

H+

H+

H+

H+

ATPsynthase

H+H+

ADPATP

Photosystem I Second chlorophyll complex Re-energizes “used” electron

freeenergy

(G)

e-

e-e-

e-

NADPH

ph

oto

sys

tem

II

ph

oto

sys

tem

I

lightlight

ATPADP

NADP

Electron transport Electron transferred to NADP+ → NADPH Electrons transferred to Photosystem I

Photosystem I

stroma

thylakoid space

H2O O2

H+

H+

e–

H+

H+

H+H+

H+

cytochromeoxidasecomplexphotosystem II photosystem I

NADP+NADPH

Light-dependent reactions Capture light energy as ATP and NADPH Why does the plant want NADPH?

freeenergy

(G)

e-

e-e-

e-

ph

oto

sys

tem

II

ph

oto

sys

tem

I

lightlight

ATPADP NADPH

NADP

Light-independent (“dark”) reactions

Why does the plant want to make glucose?

CO2 glucose

ATP NADPH

Light-independent (“dark”) reactions CO2 reduced to make glucose Occurs in stroma Calvin cycle

CO2

glucose

ATP

NADPH

3C carbohydrate

Light-independent (“dark”) reactions Key reaction catalyzed by RuBisCo

Ribulose bisphosphate carboxylase Most abundant enzyme!

5C

CO2

6C

3C3C

RuBisCo

Photosynthesis

CO2

light

H2O

O2

H+

ATPADP NADPHNADP

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