AP Biology
Photosynthesis Details
AP Biology
§ Chloroplastsu double membraneu stroma
§ fluid-filled interioru thylakoid sacsu grana stacks
§ Thylakoid membrane containsu chlorophyll moleculesu electron transport chainu ATP synthase
§ H+ gradient built up within thylakoid sac
Plant structure H+H+
H+H+
H+H+
H+H+H+H+
H+
outer membrane inner membrane
thylakoidgranum
stroma
thylakoid
chloroplast
ATP
AP Biology
Photosynthesis
§ Light reactionsu light-dependent reactionsu energy conversion reactions
§ convert solar energy to chemical energy§ ATP & NADPH
§ Calvin cycleu light-independent reactionsu sugar building reactions
§ uses chemical energy (ATP & NADPH) to reduce CO2 & synthesize C6H12O6
It’s not theDark Reactions!
AP Biology
§ Electron Transport Chain§ like in cellular respiration
u proteins in organelle membrane u electron acceptors
§ NADPHu proton (H+)
gradient across inner membrane§ find the double membrane!
u ATP synthase enzyme
Light reactionsH+H+
H+H+
H+H+H+H+
H+H+H+
H+H+H+H+
H+H+H+H+
H+H+H+ATP
thylakoidchloroplast
AP Biology
Mitochondria transfer chemical energy from food molecules into chemical energy of ATP
u use electron carrier NADH
ETC of Respiration
generates H2O
AP Biology
ETC of Photosynthesis Chloroplasts transform light energy into chemical energy of ATP
u use electron carrier NADPH
generates O2
AP Biology
ATP Synthase
§ moves the electrons § runs the pump§ pumps the protons§ builds the gradient§ drives the flow of protons
through ATP synthase§ bonds Pi to ADP§ generates the ATP
sunlight breakdown of C6H12O6
respirationphotosynthesis
H+
ADP + Pi
H+ H+
H+
H+ H+
H+H+H+
ATP
AP Biology
Pigments of photosynthesis
§ Chlorophylls & other pigmentsu embedded in thylakoid membraneu arranged in a “photosystem”
§ collection of moleculesu structure-function relationship
How does thismolecular structurefit its function?
AP Biology
Photosystems of photosynthesis § 2 photosystems in thylakoid membrane
u collections of chlorophyll molecules u act as light-gathering moleculesu Photosystem II
§ chlorophyll a§ P680 = absorbs 680nm
wavelength red light u Photosystem I
§ chlorophyll b§ P700 = absorbs 700nm
wavelength red light
reactioncenter
antennapigments
AP Biology
ETC of PhotosynthesisPhotosystem II
Photosystem I
chlorophyll a
chlorophyll b
AP Biology
1
ETC of Photosynthesis
ee
sun
Photosystem IIP680
chlorophyll a
AP Biology
12
ETC of Photosynthesis
Photosystem IIP680
chlorophyll a
OH H
H
H
Inhale, baby!
e e
ee
e-e-
H+H+H+H+
H+H+H+H+
H+H+H+
H+H+H+H+
H+H+H+H+
H+H+H+ATP
thylakoidchloroplast
H+ +H
OO
AP Biology
12 H+
H+
3
4
H+
ADP + Pi
H+ H+
H+
H+ H+
H+H+H+
ee
ATP
to Calvin Cycle
energy to buildcarbohydrates
H+H+H+H+
H+H+H+H+
H+H+H+
H+H+H+H+
H+H+H+H+
H+H+H+ATP
thylakoidchloroplast
Photosystem IIP680
chlorophyll a
ETC of Photosynthesis
ATP
AP Biology
ee sun
5
Photosystem IIP680
chlorophyll a
Photosystem IP700
chlorophyll b
e e
ETC of Photosynthesis
AP Biology
6
electron carrier
ee
5sun
Photosystem IIP680
chlorophyll a
Photosystem IP700
chlorophyll b
ETC of Photosynthesis
AP Biology
split H2O
ETC of Photosynthesis
O
ATP
to Calvin CycleH+
H+H+
H+
H+H+
H+
H+
H+H+
H+
sun sun
AP Biology
ETC of Photosynthesis§ ETC uses light energy to produce
u ATP & NADPH§ go to Calvin cycle
§ PS II absorbs lightu excited electron passes from chlorophyll to
“primary electron acceptor”u need to replace electron in chlorophyllu enzyme extracts electrons from H2O &
supplies them to chlorophyll§ splits H2O§ O combines with another O to form O2§ O2 released to atmosphere§ and we breathe easier!
AP Biology
6CO2 6H2O C6H12O6 6O2light
energy ®+ ++
Experimental evidence§ Where did the O2 come from?
u radioactive tracer = O18
6CO2 6H2O C6H12O6 6O2light
energy ®+ ++
Experiment 1
6CO2 6H2O C6H12O6 6O2light
energy ®+ ++
Experiment 2
Proved O2 came from H2O not CO2 = plants split H2O!
AP Biology
Noncyclic Photophosphorylation§ Light reactions elevate
electrons in 2 steps (PS II & PS I)u PS II generates
energy as ATPu PS I generates
NADPH
ATP
AP Biology
Cyclic photophosphorylation§ If PS I can’t pass electron
to NADP…it cycles back to PS II & makes more ATP, but no NADPHu coordinates light
reactions to Calvin cycleu Calvin cycle uses more
ATP than NADPH
7
18 ATP +12 NADPH 1 C6H12O6®
ATP
AP Biology
Photophosphorylation
NONcyclicphotophosphorylation
cyclicphotophosphorylation
ATP
NADP
AP Biology
Lets Review!
Photosystems Animation
AP Biology
Photosynthesis summary Where did the energy come from?Where did the electrons come from? Where did the H2O come from?Where did the O2 come from?Where did the O2 go? Where did the H+ come from?Where did the ATP come from?What will the ATP be used for? Where did the NADPH come from?What will the NADPH be used for?
…stay tuned for the Calvin cycle
AP Biology
Calvin Cycle
Light Independent Reactions
AP Biology
Light reactions§ Convert solar energy to chemical
energyuATPuNADPH
§ What can we do now?
® energy® energy carrier
®® build stuff !!photosynthesis
ATP
AP Biology
How is that helpful?§ Want to make C6H12O6
u synthesisu How? From what?
What raw materials are available?
CO2
C6H12O6
NADPH
NADPcarbon fixation
NADP
AP Biology
From CO2 ® C6H12O6§ CO2 has very little chemical energy§ C6H12O6 contains a lot of chemical energy§ Synthesis = endergonic process
u put in a lot of energy § CO2® C6H12O6 proceeds in many small
uphill stepsu each catalyzed by a specific enzymeu using energy stored in ATP & NADPH
AP Biology
From Light reactions to Calvin cycle§ Calvin cycle
u chloroplast stroma§ Need products of light reactions to
drive synthesis reactionsu ATPu NADPH
stroma
thylakoid
ATP
AP Biology
To G3P and Beyond!§ Glyceraldehyde-3-P
u end product of Calvin cycleu energy rich 3 carbon sugaru “C3 photosynthesis”
§ G3P is an important intermediate§ G3P ®®glucose ®® carbohydrates
®® lipids ®® phospholipids, fats, waxes®® amino acids ®® proteins®® nucleic acids ®® DNA, RNA
To G3Pand beyond!
AP Biology
Calvin Cycle§ Main part of light-independent reaction
u Doesn't need light, but only occurs in lightu Uses products from light reaction (ATP and NADPH)
§ Cyclic process: produces 3-carbon sugar PGAL or G3P
§ Carbon Fixation: Carbon enters leaf as CO2, becomes fixed as PGAL
§ Net synthesis of one G3P moleculeu Nine ATP and 6 NADPH molecules were used.u G3P is the starting material for metabolic pathways that
synthesize other organic compounds, including glucose.§ ADP & NADP are passed to the light reactions and
used to regenerate ATP and NADPH.
AP Biology
AP Biology
Photosynthesis summary§ Light reactions
u produced ATPu produced NADPHu consumed H2Ou produced O2 as byproduct
§ Calvin cycleu consumed CO2u produced G3P (sugar)u regenerated ADPu regenerated NADP NADPADP
AP Biology
Light Reactions
O2
H2O
Energy BuildingReactions
ATP
§ produces ATP§ produces NADPH§ releases O2 as a
waste product
sunlight
H2O ATP O2light
energy ® ++ + NADPH
NADPH
AP Biology
Calvin Cycle
sugars
CO2
SugarBuilding
Reactions
ADP
§ builds sugars§ uses ATP &
NADPH§ recycles ADP
& NADP § back to make
more ATP & NADPHATP
NADPH
NADP
CO2 C6H12O6® ++ + NADPATP + NADPH ADP
AP Biology
Putting it all togetherCO2 H2O C6H12O6 O2
lightenergy ®+ ++
SugarBuilding
Reactions
Energy Building
Reactions
Plants make both:§energy§ATP & NADPH
§sugars
sunlight
O2
H2O
sugars
CO2
ADP
ATP
NADPH
NADP
AP Biology
H2O
Energy cycle
Photosynthesis
Cellular Respiration
sun
glucose O2CO2
plants
animals, plants
ATPThe Great Circleof Life,Mufasa!
CO2 H2O C6H12O6 O2light
energy ®+ ++
CO2 H2OC6H12O6 O2ATP
energy®+ ++
AP Biology
Summary of photosynthesis
§ Where did the CO2 come from?§ Where did the CO2 go?§ Where did the H2O come from?§ Where did the H2O go?§ Where did the energy come from?§ What’s the energy used for?§ What will the C6H12O6 be used for?§ Where did the O2 come from?§ Where will the O2 go?§ What else is involved…not listed in this equation?
6CO2 6H2O C6H12O6 6O2light
energy ®+ ++
AP Biology
Supporting a biosphere§ On global scale,
photosynthesis is the most important process for the continuation of life on Earthu each year photosynthesis…
§ captures 121 billion tons of CO2
§ synthesizes 160 billion tons of carbohydrate u heterotrophs are dependent on plants as
food source for fuel & raw materials
AP Biology
The poetic perspective…§ All the solid material of every plant
was built by sunlight out of thin air§ All the solid material of every animal
was built from plant material
Then all the plants, cats, dogs, elephants & people …
are really particles of air woven together by strands of sunlight!
sunair
AP Biology
Factors affecting photosynthesis�Factor - any of certain substances
necessary to a biochemical or physiological process
�Limiting Factor - any factor that causes the rate of a reaction to plateau or decrease, i.e. limiting the reaction
�Optimum - the best or most favorable point, degree, amount, etc., as of temperature, light, and moisture for the growth or reproduction of an organism
AP Biology
Factors Affecting Photosynthesis§ Water Availability§ Light Intensity§ CO2 Availability§ Nutrient Availability
u Magnesiumu Nitrogen
AP Biology 2007-2008
Photosynthesis:Variations on the Theme
AP Biology
Alternative mechanisms for Carbon Fixation
§ Plant adaptations that prevent dehydration may also reduce availability of CO2
§ On hot, dry days, most plants (C3 plants) close their stomata to conserve water.
§ When stomata close, CO2 levels drop as CO2 is consumed in the Calvin Cycle
§ At the same time, O2 levels rise as the light reaction converts light to chemical energy
AP Biology
C4 Plants§ C4 plants fix CO2 into a four-carbon
compound§ Several thousand plants use this including
sugar cane and corn§ Modification for dry environments
u Minimize water loss and maximize sugar production
AP Biology
CAM plants§ These plants open stomata during the
night and close them during the day.§ Temperatures are typically lower at night &
humidity is high§ Includes cacti, pineapples
§ At night, CAM plants fix CO2 into a variety of organic acids in mesophyll cells.
§ During the day, the light reactions supply ATP and NADPH to Calvin cycle and CO2 is released from organic acids.