ps lecture outline - blogs.4j.lane.edublogs.4j.lane.edu/.../09/01_photosynthesisnotes_ib.pdf ·...

PS Lecture OutlineI. Introduction

A. StructuresB. Net Reaction

II. Overview of PSA. Rxns in the chloroplastB. pigments

III. Closer looksA. LD RxnsB. LI Rxns

1. non-cyclic e- flow2. cyclic e- flow3. chemiosmosis

C. Calvin CycleD. Alternative C-fixations

IV. Variables in PS effectiveness

Vein

Leaf cross section

Mesophyll

CO2 O2Stomata

A. Structures of PS• Site of PS in plants:

• mostly in leaves• in chloroplasts

Inside the chloroplast

• Identify the structures in the diagram

Chloroplast

Mesophyll

5 µm

Outer membrane

Intermembrane space

Inner membrane

Thylakoid space

Thylakoid

GranumStroma

1 µm

• Chloroplasts

• thylakoids

• grana

• stroma

6H2O + 6CO2 ------> C6H12O6+ 6O26 waters

6 carbon dioxides(plus light E, makes...)

1 glucose6 oxygen

B. The Net Reaction of Photosynthesis

Net Reaction• hydrolysis

• e- of H --> sugar• O --> O2

6 CO2 12 H2OReactants:

Products: C6H12O6 6 H2O 6 O2

Figure 10.4Photosynthesis is a redox process

Water is oxidized, carbon dioxide is reduced

• we will stay (mostly) conceptual

• follow the energy

II. PS Overview

• Occur in the grana1. capture photons2. split water3. release oxygen4. produce ATP

a. “photophosphoryllation driven by chemiosmosis”b. E transfer

5. form NADPH• E transfer

A. Light Dependant Rxns

• aka The Calvin cycle• in the stroma1. forms sugar from carbon dioxide2. uses ATP for energy3. uses NADPH for reducing power

B. Light Independent Rxns

PS Overview

PS Overview

PS Overview

• How does the chloroplast absorb light?

• Pigments

• chlorophyll a,b

• accessory pigments

Photosynthetic Pigments: The Light Receptors

III. Closer look at LD Rxns

Excited state

Ene

rgy

of e

lect

ion

Heat

Photon (fluorescence)

Chlorophyll molecule

Ground statePhoton

e–

Figure 10.11 A

• When a pigment absorbs light

• ground state --> excited state (unstable)

Excitation of Chlorophyll by Light

Photosystems• Light harvesting

complexes• aka “antenna

pigment mols”• pigment mols

bound by proteins

• funnel energy to reaction center

• e- gets bumped• p680 (PSII)• p700 (PSI)

Primary election acceptor

Photon

Thylakoid

Light-harvesting complexes

Reaction center

Photosystem

STROMA

Thyl

akoi

d m

embr

ane

Transfer of energy

Special chlorophyll a

molecules

Pigment molecules

THYLAKOID SPACE (INTERIOR OF THYLAKOID)Figure 10.12

e–

Mill makes ATP

ATP

e–

e–e–

e–

e–

Phot

on

Photosystem II Photosystem I

e–

e–

NADPH

Phot

on

Figure 10.14

Analogy for the Lt Rxns

Noncyclic electron flow• Produces NADPH, ATP, and oxygen

© 2014 Pearson Education, Inc.

The biomass (dry weight) of a tree comes primarily from

A. soil. B. water. C. air. D. organic fertilizer (manure, detritus). E. light.

© 2014 Pearson Education, Inc.

The light reactions, which involve the very hydrophobic chlorophyll, are located here in the chloroplast.

A.

B.C. (lumen)

E.

D.

© 2014 Pearson Education, Inc.

What colors of light will drive photosynthesis by green plants most efficiently?

A. red only B. yellow only C. green only D. blue only E. red and blue

© 2014 Pearson Education, Inc.

How are the light reactions and the Calvin cycle connected?

A. The light reactions provide ATP to the Calvin cycle, and the Calvin cycle provides NADPH for the light reactions.

B. The light reactions provide ATP and NADPH to the Calvin cycle, and the Calvin cycle returns ADP and NADP+ to the light reactions.

C. The light reactions provide ATP and NADPH to the Calvin cycle, and the Calvin cycle returns reduced sugars to the light reactions.

D. The light reactions provide NADPH to the Calvin cycle, and the Calvin cycle provides RuBP to the light reactions.

E. The light reactions provide RuBP to the Calvin cycle, and the Calvin cycle returns G3P to the light reactions.

• Occurs:

• Sim to Citric Acid Cycle (aka Krebs) in CR

• opposite of anaerobic glycolysis

• 3 phases

• C-fixation

• Reduction

• Regeneration of the CO2 acceptor

Calvin Cycle

(G3P)

Input(Entering one

at a time)CO2

3

RubiscoShort-lived

intermediate

3 P P

3 P PRibulose bisphosphate

(RuBP)

P

3-Phosphoglycerate

P6 P

6

1,3-Bisphoglycerate6 NADPH

6 NADPH+

6 P

P6

Glyceraldehyde-3-phosphate (G3P)

6 ATP

3 ATP

3 ADP CALVIN CYCLE

P5

P1 G3P (a sugar)Output

LightH2O CO2

LIGHTREACTION

ATP

NADPH

NADP+

ADP

[CH2O] (sugar)

CALVIN CYCLE

Figure 10.18

O2

6 ADP

Glucose andother organiccompounds

Phase 1: Carbon fixation

Phase 2:Reduction

Phase 3:Regeneration ofthe CO2 acceptor

(RuBP)

The Calvin Cycle

The Calvin Cycle• Starts w/ CO2 + enzyme Rubisco +RuBP

• 3 “turns” of Calvin make...

• 3-C sugar

• 6 “turns” = 1 glucose

The Calvin Cycle• Three phases...

• Fixation

• CO2 + RuBP + Rubisco

• Reduction

• requires ATP (for E)

• requires H (from NADPH)

• produces 3-C sugars: G3P

• 1/6 of which form Glu

• Regeneration

• 5/6 of 3-C sugars regenerate RuBP

• requires ATP

• aka Cyclic Phosphoryllation

• Under certain conditions

• ATP deficit

• excess NADPH, deficit of NADP+

• bumped e-’s take an alternative path

• generates ATP

Cyclic Electron Flow

• Only photosystem I is used• Only ATP is produced (no O2 or NADPH)

Primary acceptor

Pq

Fd

Cytochrome complex

Pc

Primary acceptor

Fd

NADP+

reductaseNADPH

ATPFigure 10.15 Photosystem II Photosystem I

NADP+

Cyclic Electron Flow

Alternative C-Fixations• What do plants do on hot, arid days?

• close their stomata

• What happens to PS reactants/prods?

• water conserved

• less CO2

• O2 build up

• Leads to Photorespiration

• O2 substitutes for CO2 in the active site of the enzyme rubisco

• Rate PS decreases

Minimizing Photorespiration

• C4 plants

• avoid photorespiration spatially

• CO2 stored as 4-C compounds

• stored in mesophyll cells• exported to bundle

sheath cells

• release CO2 to the Calvin cycle

CO2

Mesophyll cell

Bundle- sheath

cell

Vein (vascular tissue)

Photosynthetic cells of C4 plant

leaf

Stoma

Mesophyll cell

C4 leaf anatomy

PEP carboxylase

Oxaloacetate (4 C) PEP (3 C)

Malate (4 C)

ADP

ATP

Bundle- Sheath

cell CO2

Pyruvate (3 C)

CALVIN CYCLE

Sugar

Vascular tissue

Figure 10.19

CO2

C4 Path

Minimizing Photorespiration

• CAM plants• avoid photorespiration

temporally• Open their stomata at

night

• incorporating CO2 into organic acids

• CO2 released during the day to CC

Spatial separation of steps. In C4 plants,

carbon fixation and the Calvin cycle occur in

different types of cells.

(a) Temporal separation of steps. In CAM plants, carbon fixation and the

Calvin cycle occur in the same cells

at different times.

(b)

PineappleSugarcane

Bundle- sheath cell

Mesophyll Cell

Organic acid

CALVIN CYCLE

Sugar

CO2 CO2

Organic acid

CALVIN CYCLE

Sugar

C4 CAM

CO2 incorporated into four-carbon organic acids

(carbon fixation)

Night

Day

1

2 Organic acids release CO2 to

Calvin cycle

Figure 10.20

C4 vs CAM

Effect of Light Intensity

• low light => not enough ATP, NADPH

• what would be rate limiting step in Calvin Cycle?

• unusual unless the plant is heavily shaded

Effect of CO2 Concentration

• low CO2 => what would be rate-limiting step?

• this is a common limiting factor

Effect of Temperature

• low temps => rate of rxn = ____

• high temps => CO2 fixation doesn’t work