Lecture 3 Outline (Ch. 8)I. Photosynthesis overview

A. Purpose B. Location

II. The light vs. the “dark” reaction

III. Chloroplasts pigments A. Light absorption B. Types

IV. Light reactions A. Photosystems B. Photophosphorylation

V. The light independent reaction (“dark” reaction) A. Carbon “fixation” B. Reduction C. Regeneration

VI. Alternative plants

Photosynthesis - overview

Overall purpose:

Photosynthesis - overview

• photosynthesis –

light chemical energy

• complements respiration

Energy for all life on earth ultimately comes from photosynthesis

Cellular Respiration:(Exergonic)

Photosynthesis:(Endergonic)

Cellular Respiration vs. Photosynthesis

Photosynthesis – chloroplast recap

Outer membrane

Inner membrane

Thylakoid membrane

Stroma

Thylakoid space

Intermembrane space

Photosynthesis - overview

• Photosynthesis -

1. light rxn: store energy & split water – “photo”

2. dark rxn: “fix” CO2 & make sugars – “synthesis”

Calvin cycle

NADPH & ATP

Redox Reactions

Equation for photosynthesis

6CO2 + 12H2O + light energy C6H12O6 + 6O2 + 6H2O

Photosynthesis - overview

– thylakoid membrane

– thylakoid space– stroma

• light reactions: • dark reactions:

Light

H2O

Chloroplast

LightReactions

NADP+

PADP+

ATP

NADPH

O2

CalvinCycle

CO2

[CH2O]

(sugar)

Photosynthesis – light absorption

• visible light ~380 to 750 nm

• chloroplast pigments – abs blue-violet & red

- transmit and reflect green

• pigments:

• chlorophyll a

• accessory pigments

-energy-absorbing ring

-hydrocarbon tail

- carotenoids

- photoprotective

Photosynthesis – light absorption

- chlorophyll b

• chlorophyll a – abs blue-violet, red

400-450, 650-700 nm

• chlorophyll b & carotenoids – abs broadly blue-violet

mid-400s

• more wavelengths used for photosynthesis = more light energy absorbed

Photosynthesis – light absorption

• chlorophyll abs light

Photosynthesis – light absorption

• e- excited

• more energy

• energy transferred

Pigments have two states: ground & excited

Photosynthesis – light absorption

light harvesting complex

• energy absorbed from light - to pigments

• to reaction center

- two special chlorophyll a

- 1° electron acceptor

• light harvesting complex & reaction center = photosystem (PS)

- proteins

Pigments are held by proteins in the thylakoid membranes

Photosynthesis – energy transfer

• Photosystem I (PS I) & PS II

• Difference – light wavelength, proteins, where e- from

Light

Thylakoidmembrane

THYLAKOID SPACE

STROMA

Photosystem II Photosystem I

Light

Photosynthesis – energy transfer

• PSII: absorbs 680 nm,

• PS I: absorbs 700 nm,

(less energy)

splits water, powerful ETC, ATP made

e- from PSII, short ETC, NADPH made

Photosynthesis – energy transfer

• e- from PS II electron transport chain (ETC) PS I

NADPH• e- from PS I 2nd ETC e- carrier: NADP+

• e- in PS II, from split H20

Photosynthesis – chemiosmosis

• How is ATP produced?

Chemiosmosis

photophosphorylation

• e- down ETC, H+ to thylakoid space

• H+ conc. gradient

• H+ down gradient, ATP synthase

Light reaction - summary

• inputs: light energy, H2O

• PS II, ETC, PS I, ETC

• outputs:

ATP

NADPH

O2 (waste)

Self-Check

Step of Photosynthesis

Location IN chloroplast

Inputs Outputs ATP produced?

(don’t need #)

e- carriers loaded?

Light reaction overall

PSII

PSI

“Dark” reaction overall

Know figures of chloroplast reactions/locations!

Photosynthesis – energy transfer

“Dark” reaction (Light-independent Reaction)

6CO2 + 12H2O + light energy C6H12O6 + 6O2 + 6H2O

• “Dark” reaction: Calvin cycle

• regenerative

• anabolic

• CO2 in, sugar out

• during daylight

CO2

NADP+

ADPPi+

RuBP 3-PhosphoglycerateCalvinCycle

G3PATP

NADPH Starch(storage)

Sucrose (export)

Chloroplast

Light

H2O

O2

Carbon fixation

• 3 stages of Calvin-cycle:

• #1 – carbon fixation

• CO2 link to 5-C

• 5-C: ribulose bisphosphate (RuBP) - enzyme: Rubisco

abundant

• 6-C unstable – split 2(3-C)

Reduction

• #2 – reduction

• reduced 3-C: G3P

• 3-C reduced

• e- from NADPH

• 3 stages of Calvin-cycle:

Regeneration of C-acceptor

• multiple steps

• uses ATP

• every 3 cycles:

1 G3P made

3 RuBP regenerated

• #3 – regenerate C-acceptor

• still 5 G3P 3 RuBP

• C3 plants – CO2 fixed into 3-C

• 3 stages of Calvin-cycle:

Self-Check

Step of Photosynthesis

Location IN chloroplast

Inputs Outputs ATP produced

(don’t need #)

e- carriers loaded

Light reaction overall

PSII

PSI

“Dark” reaction overall

Alternate methods of C fixation

Alternate methods of C fixation

CO2

NADP+

ADPPi+

RuBP 3-PhosphoglycerateCalvinCycle

G3PATP

NADPH Starch(storage)

Sucrose (export)

Chloroplast

Light

H2O

O2

• CO2 in stomata

• open, lose water

• O2 fixed – photorespiration – inefficient

• hot, dry – open stomata less; lowers water loss, lowers CO2

• fix CO2 into 4-C molecules

Photosynthesis – summary

• light reaction: Light energy + H2O

• light-independent:

CO2, NADPH, ATP

O2, NADPH, ATP

Thylakoids

G3P (sugar), RuBP

Stroma

Photosynthesis – summary

Where do photosynthetic products go?

Photosynthesis – in context of big picture

Lecture 3 Summary

1. Photosynthesis Overview (Ch. 8)- Purpose- Redox reactions- Electron carriers & sugars

2. Light (Ch. 8)- Absorption pigments- Light spectra/wavelengths

3. Locations of steps, inputs/outputs, purpose, description (Ch. 8)- PSI vs. PS II- Whole light reaction [includes chemiosmosis]- “dark” reaction/Calvin cycle [3 steps]

4. Alternate modes of photosynthesis (Ch. 8)

5. Photosynthesis context (Ch. 8)

- Uses for products

- Relationship of cell respiration and photosynthesis