Key Themes Energy acquisition in photosynthesis: from sunlight to ATP & sugar production Lecture 8:...

Key Themes

Energy acquisition in photosynthesis: from sunlight to ATP & sugar production

Lecture 8: Photosynthesis

Yesterday’s Exit Ticket

Glucose

Process: Gycolysis

Location: Cytosol

# ATPs:

Citric Acid Cycle

Location: Mitochon. MatrixProducts Released: CO2

Location: Mitoch. Inner MembraneProducts Released: H20

# ATPs:

# ATPs:

Oxidative Phosphorylation

2

NADH NADH + FADH2

Pyruvate

2 2 34

Time to Photosynthesize!

Fig. 1.5

Sunlight

Ecosystem

Heat

Heat

Cyclingof

chemicalnutrients

Producers(plants and other photosynthetic

organisms)

Chemical energy

Consumers(such as animals)

PhotosynthesisSun = ultimate energy source

Mint kept mouse alive, but not in the basement…

http://www.americanscientist.org/issues/id.800,y.1998,no.6,content.true,page.1,css.print/issue.aspx

"the injury which is continually done to the atmosphere by the respiration of such a large number of animals ... is, in part at least, repaired by the vegetable creation"

Joseph Priestly, 1771-1772

http://home.nycap.rr.com/useless/priestly/priestly.html

(a) Plants

(c) Unicellular protist

10 µm

1.5 µm

40 µm(d) Cyanobacteria

(e) Purple sulfur bacteria

(b) Multicellular alga

PhotosyntheticOrganisms

Fig. 10.2

What is the goal of photosynthesis?

• Light Chemical Energy• Form C-H bonds for energy storage• Harness the sun’s energy to do so

Sugar [CH2O] + O2

Light + CO2 + H20(energy)

O2 + some ATP sugarsH2O

H+ & e-

CO2Light

dermalinstitute.com; gaia-health.com

O2 + some ATPH2O

H+ & e-

Light

Step 1: Light-Dependent

Reactions



H+ & e-

CO2Light

Step 2: Light-Independent

Reactions(Calvin Cycle)


Overview of Photosynthesis

solar energy

Solar energy drives production of energy-rich ATP & NADPH

ATP & NADPH drive conversion of CO2 to energy-rich sugar

Fig. 10.5

O2 is a waste product

O2

Because ATP is too unstable to serve as a storage form of energy, C-H bonds in sugars are instead

used for energy storage.

Fig. 8.8

ATP: Energy carrier

solar energy

Fig. 10.5

Step 1: Light-Dependent Reactions• Occur in: thylakoid membranes of chloroplasts• Start with: H2O, NADP+, ADP, Pi• Produce: NADPH, ATP, and O2

O2

Leaf cross section Vein

Stomata CO2 O2

Mesophyll cell

5 µmThylak

oidspace

Thylakoid

Granum

Stroma

1 µm

Fig. 10.3

Plant photosynthesis occurs in chloroplasts

Chloroplast

Leaf cross section Vein

Stomata CO2 O2

Chloroplast

5 µmThylakoid

space

Thylakoid

GranumStroma

1 µm

Fig. 10.3

Plant photosynthesis occurs in chloroplasts

• Inner membranes (thylakoids): Light reactions (light collection by chlorophyll & electron transport)

• Fluid space (stroma): Conversion of CO2 to sugars in Calvin cycle

Photosystems made up of chlorophylls

absorb sunlight

Photosystems use light energy to

propel energized electrons into the

photosynthetic electron transport

chain

Fig. 10.14

e-

• Most chlorophylls absorb light energy & pass it on to a special chlorophyll that gives up an electron.

Fig. 10.12

H2O H+ +

O2

water-splitting enzyme

e-

• This special chlorophyll gets an electron back from a water molecule, leaving behind H+ (protons*) and O2.

*H = 1 proton + 1 electron

e-

• The energized electron is propelled through the electron transport chain.

Fig. 10.12

H2OH+ + O2

e-

Fig. 10.14

Light

ADP +

i H+

ATPP

ATPsynthase

ToCalvinCycle

STROMA(low H+ concentration)

Thylakoidmembrane

THYLAKOID SPACE(high H+ concentration)

STROMA(low H+ concentration) Photosystem

IIPhotosystem I4 H+

4 H+

Light

NADP+ + H+

NADPH

+2 H+

H2O O2

e–

e– 1/21

2

3

NADP+reductase

Now, let’s look at this whole process within the context of the thylakoid membranes

Fig. 10.17

Here’s an animation of photosynthetic electron transport.

http://www.colorado.edu/ebio/genbio/10_17LightReactions_A.html

“When sunlight is absorbed into a plant, it triggers a chain reaction of electrons, which move from one molecule to the next…

The Berkeley researchers borrowed this [chain reaction] for their artificial forest, but instead of relying on the pigment in chloroplast to trigger electron movement they used semiconductors.”



H+ & e-(NADPH)

CO2

Light


Original electron donor in photosynthesis

Electron acceptors from ETC: NADP+

Electron donors for Calvin cycle Electron acceptor

from Calvin cycle

Protons are pumped into the inner thylakoid space and ATP is formed in the stroma

Light

ADP +

i H+

ATPP

ATPsynthase

ToCalvinCycle

STROMA(low H+ concentration)

Thylakoidmembrane


STROMA(low H+ concentration) Photosystem

IIPhotosystem I4 H+

4 H+

Light

NADP+ + H+

NADPH

+2 H+

H2O O2

e–

e– 1/21

2

3

NADP+reductase

Fig. 10.17

+

Pi

H+

ADP

ATP

Fig. 9.14

Light

ADP i H

+

ATPP

ATPsynthaseSTROMA

(low H+ concentration)

Thylakoidmembrane


STROMA(low H+ concentration)Photosystem

IIPhotosystem I4

H+

4 H+

Light

+2 H+

H2O O

2

e–

e– 1/

2

NADP+reduct

ase

P i

Inner thylakoid space

stroma

The ATP synthase “turbine”

Fig. 10.16

Same principle used for ATP formation in chloroplasts & mitochondria

Fig.8.7


H+ & e-

CO2

Light

Step 1: Light-Dependent

Reactions

NADP+

NADPH



CO2

Light

Step 2: Light-Independent

Reactions(Calvin Cycle)

H+ & e-

NADP+

NADPH


solar energy

Fig. 10.5

Step 2: Calvin Cycle• Occurs in: stroma (liquid space inside chloroplasts)• Starts with: CO2, NADPH, ATP• Produces: Sugar, NADP+, ADP, Pi

O2

LightReactions:

Light collection & electron transport

CO2

NADP+

ADPP i+

RuBP 3-PhosphoglycerateCalvin

Cycle

G3PATP

NADPHStarch(storage)

Sucrose (export)

Chloroplast

Light

H2O

O2Fig. 10.21 O2

LightReactions:


CO2

NADP+

ADPP i+

RuBP 3-Phosphoglycerate

Calvin

Cycle

G3PATP


Sucrose (export)

Chloroplast

Light

H2O

O2Fig. 10.21

Rubisco:combines RuBP with

CO2 to form 3-PG

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

In this diagram of the Calvin cycle, compound X is the CO2 acceptor. If

CO2 is cut off, then

A. X and 3PG will both increase.

B. X will increase, 3PG decrease.

C. X will decrease, 3PG increase.

D. X and 3PG will both decrease.


• Light Chemical Energy• Form C-H bonds for energy storage• Harness the sun’s energy to do so

Sugar [CH2O] + O2

Light + CO2 + H20(energy)


H+ & e-

CO2

Light


5 min break

Wtfcontent.com

http://www.youtube.com/watch?v=sQK3Yr4Sc_k&feature=fvwrel

Hank’s Crash Course in Photosynthesis

Plant adaptations to their environments

Flickriver.com

What does a plant need?

Light, CO2, H2O, (nutrients)

Travelsfy.com

LightReactions:


CO2

NADP+

ADP

P i+

RuBP 3-Phosphoglycerate

Calvin

Cycle

G3PATP


Sucrose (export)

Chloroplast

Light

H2O

O2

Fig. 10.21

Acclimation to sun vs. shade?

Sun

Calvin Cycle enzymes

Shade

+++

+

When LIGHT varies:


When H2O varies:


Travelsfy.com

Stomate

Stomata

CO2H2O

O2

When H2O varies:

Light, CO2, H2O, (nutrients)Travelsfy.com; minnestota.publicradio.org; mccullagh.org

CO2H2O

O2

In wet environments

• Stomata can stay wide open• CO2 is relatively unlimited in

plant cells

In semi-arid environments

• Stomata are kept ajar to reduce water loss

• CO2 is acquired more slowly

In dry environments

• Stomata are kept closed in the heat of the day

• Stomata are opened at night to acquire CO2

When H2O varies:

Light, CO2, H2O, (nutrients)Travelsfy.com; minnestota.publicradio.org; mccullagh.org

In wet environments• Stomata can stay wide open• CO2 is relatively unlimited in

plant cells

In semi-arid environments

• Stomata are kept ajar to reduce water loss

• CO2 is acquired more slowly

In dry environments• Stomata are kept closed in

the heat of the day• Stomata are opened at night

to acquire CO2

“C3”Most plants

More “C4” plantsMany grasses

More “CAM” plantsCacti, many other desert succulents

Most plants (C3 plants) use only Calvin cycle: First product has 3 carbons (phosphoglycerate).

LightReactions:


CO2

NADP+

ADPPi+

RuBP

3-Phosphoglycerat

eCalv

inCycl

e

G3P

ATP

NADPH

Starch(storage)

Sucrose (export)

Chloroplast

Light

H2O

O2Fig. 10.21

Most plants (C3 plants) use only Calvin cycle: First product has 3 carbons (phosphoglycerate).

The C4 pathway

CO2PEP carboxylase

Oxaloacetate (4C)

Malate (4C)

PEP (3C) AD

PATP

Pyruvate (3C)CO2

CalvinCycle

Sugar

Vasculartissue

Fig. 10.19

Some plants (C4 plants) use an additional CO2 fixation cycle before the Calvin cycle: The enzyme PEP carboxylase “fixes” CO2 into a sugar with 4 carbonsOnce enough new CO2 has been stored in the 4-C sugar, it moves into the Calvin Cycle Leaf surface

Inside of leaf

C4 plants:• This process allows the Calvin Cycle to run smoothly

despite low CO2 conditions

The C4 pathway

Mesophyllcell

CO2PEP carboxylase

Oxaloacetate (4C)

Malate (4C)

PEP (3C) AD

PATP

Pyruvate (3C)CO2

Bundle-sheathcell

CalvinCycle

Sugar

Vasculartissue

Fig. 10.19

CAM plants:• Take the C4 process one step further

The C4 pathway

Mesophyllcell

CO2PEP carboxylase

Oxaloacetate (4C)

Malate (4C)

PEP (3C) AD

PATP

Pyruvate (3C)CO2

Bundle-sheathcell

CalvinCycle

Sugar

Vasculartissue

• CO2 is collected and converted to 4-carbon sugar at night

• Sugar is stored in vacuoles

• In the morning, stomata close and malic acid is broken down to enter the Calvin Cycle

LightReactions:

Light harvestingand photosynthetic electron transport

CO2

NADP+

ADP

Pi+

RuBP

3-Phosphoglycerate

CalvinCycleG3PATP

NADPH Starch(storage)

Sucrose (export)

Chloroplast

Light

H2O

O2

Fig. 10.21

Why isn’t every plant a C4 plant?

Advantage of C3 plants

C3 plants need less energy since they don’t run two cycles

Advantage in less sunny, moist, cool, CO2-rich climates. Typically more cold-tolerant.

Mountainphotographer.com

Since ATP is too unstable, C-H bonds in sugars are used for energy storage.

In both mitochondria and chloroplasts:

• Carbon conversion cycles in fluid space:Calvin cycle vs. citric acid cycle (Krebs cycle)(CO2 sugar) (sugar CO2)

• Electron transport chain & ATP synthase on inner membranes (thylakoid or mitochondrial)

LightReactions:


CO2

NADP+ADPPi+

RuBP

3-Phosphoglycerat

eCalv

inCycl

eG3P

ATP

NADPH

Starch(storage)

Sucrose (export)

Chloroplast

Light

H2O

O2Fig. 10.21

Photosynthesis

Carbon source:

Carbon product:

CO2

Sugar (C-H bonds)

Ultimate energy source:

Final energy-rich product:

Sunlight

Sugar (C-H bonds)

H (electron + H+) source: Water (H-O-H)

Electrontransport

andATP synthase

Mitochondrion

ATP

Electrons carried off by

NADH & FADH2

Citricacidcycle

ATP

Glucose Pyruvate

Glycolysis

Electronscarried off by NADH

Fig. 9.6

Some SomeATP

Lots of

Cytosol

Respiration

Carbon source:

Carbon product:

Organic molecules with C-H bonds

CO2

Final energy-rich product: ATP

Energy source:C-H bondsH (electron + H+) source:

C-H bonds

Fig. 10.16

Same principle used for ATP formation in mitochondria & chloroplasts

Fig.8.7

Fig. 10.16

Citric acid cycle Calvin cycle

In both mitochondria and chloroplasts:

• Carbon conversion cycles in fluid space

• Electron transport chain & ATP synthase on inner membranes

Today’s Exit Ticket

Process:

Location:

CO2

+

H2O

O2

Fig. 10.21

Process:

Location:

Key Themes Energy acquisition in photosynthesis: from sunlight to ATP & sugar production Lecture 8:...

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