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BIOC31H3 (1)
Final

Final Exam Notes

29 Pages
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Department
Biological Sciences
Course Code
BIOC31H3
Professor
Mary Olaveson

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Photosynthesis (chapter 7, 8, 9)
Thylakoids (H20 is oxidized): H20 + light energy O2 + ATP + NADPH
Stroma (carbon fixation, C02 is reduced) : CO2 + ATP + NADPH (CH2O)
= C02 + H20 (CH20) + O2 keq= 10-500 (light driven redox process)
Hill reaction: thylakoids were isolated & given light. O2 was released and reduction of Fe happened
rather than C02 reduction. 4Fe3+ + 2H2O 4Fe2+ + O2 + 4H+
Artificial electron acceptor showed how photosynthesis & respiration worked
Light has electric and magnetic field components (electromagnetic). Energy moves in wave w/ defined
wavelength and frequency. Energy moves as particle in packets of energy called photons (quantum).
Energy of photon is inversely related to its wavelength.
Electromagnetic spectrum: shows type of radiation , F, E (gamma, xrays) , F, E (radio 
waves)
The visible spectrum can be utilized and absorbed by plants (= 400-700nm)
Fig 7.3 solar spectrum and relation to absorption of chlorophyll of light energy.
-Top curve is energy of output of sun as function of wavelength
-Second curve is energy that strikes Earth surface. It is less b/c some energy is absorbed by water
vapor in atmosphere.
-Third curve is absorption spectrum of chlorophyll which strongly absorbs in blue (430nm) and red
(660nm) spectrum portions.
When a photon of light is absorbed by chlorophyll pigment, the electron distribution is altered, and
some electrons move away from nucleus. The chlorophyll molecule then goes back to ground state.
Chl + photon (ground state) Chl* (excited state; altered e- distribution)
4 routes to dissipate energy from lowest excited state:
Note: photosynthesis doesnt use 1&2, 3&4 need to occur rapidly to compete w/ 1&2
1.Heat
2.Fluorescence: Re-emit photon of longer i.e. less energy b/c some of energy already lost as heat
3.Resonance transfer: energy transfer to another molecule, usually chlorophyll & its physical
energy transfer
4.Photochemistry: electron transfer from donor to acceptor
Fig 7.5: light absorption and emission by chlorophyll . Blue light (E photon,) Red light
(E photon,)
-All absorption of light can lead to at least the lowest excitable state which drives photochemical
and resonance transfer. The highest excited state is not very useful so it quickly dissipates to the
lowest excited state. Red light is just as good at driving photosynthesis as blue light.
Chlorophyll a & b have small structural differences but in general are a porphyrin-like ring
structure w/ central Mg and hydrophobic tail that allows for effective interaction w/ hydrophobic
bilayer of thylakoid membrane. Chlorophyll strongly absorbs in blue (430nm) and red (660nm)
absorption spectrum.
Carotenoids are orange, accessory pigments for photosynthesis that absorb 400-500nm of light and
transfer them to chlorophyll for photosynthesis. Carotenoids use that chlorophyll isnt able to use.
They have a photoprotective role to protect organism from damage caused by light.
Chlorophyll B are different b/c 1 functional group on ring is different- different absorption spectrum.
Bacteriochlorophyll a & bilin pigments are found in photosynthetic bacteria. Common to all is the
complex ring structure.
Fig 7.7 Absorption spectra of photosynthetic pigments dissolved in nonpolar solvents. However, the
true absorption spectrum of the pigments is dependent on membranes environment. Pigments shown
www.notesolution.com
in this figure are Curve 1= bacteriochlorophyll a, Curve 2=chlorophyll a, Curve 3=chlorophyll b, Curve
4=phycoerythrobilin, Curve 5=B carotene.
Fig 7.8 Absorption spectra compared w/ action spectra
Absorption spectra: effectiveness of chlorophyll molecule to absorb different light .
Action spectra: effectiveness of different light to drive some biological process (here it is O2
evolution)
-There is a very close match btw absorption and action spectra. To measure O2 concentration, light
was shined onto the alga (spirogyra)s chloroplast. Aerotactic bacteria aggregated at O2 regions
(in spectrum region where chlorophyll absorbed most effectively Blue, Red). It was first
indication of effectiveness of light absorbed by accessory pigments in driving photosynthesis.
Fig 7.11 Relationship of oxygen production to flash energy
Chlorella- short light flashes of different intensity, O2 release was measured, O2 release saturated
at high intensity.
They thought that 1chlorophyll would yield 1 O2. However, the finding was that 2500 chlorophyll
molecules would release 1 O2 at saturating energies. This was done by quantifying chlorophyll
amount and O2 amount and forming a ratio.
Reasons for 1 O2/2500 chlorophylls:
1.Hundreds of chlorophylls absorb light and transfer energy via resonance transfer until its all
funneled to 1 chlorophyll molecule (reaction center). Electron transfer then happens.
2.Each reaction center needs to operate 4 times to generate 1 O2.
3.2 different types of reaction centers (photosystems) working in series
Fig 7.10 Basic concept of energy transfer during photosynthesis
2 stages: (1) Physical transfer: many chlorophyll pigments collect light and transfer it via
resonance transfer to reaction center. (2) chemical reactions store some of energy in reaction center
by transferring e- to an acceptor mol. An e- donor then reduces the chlorophyll reaction center
again.
A. Red drop effect not consistent w/ findings.
Quantum yield = # of photochemical produces / total # of quanta absorbed
Far red light (> 680nm) is inefficient at driving photosynthesis.
Quantum yield of O2 evolution falls off drastically for far-red light of wavelengths > 680n meaning
that red light alone isnt enough at driving photosynthesis. The dip near 500nm reflects the lower
efficiency of photosynthesis using light absorbed by accessory pigments (carotenoids).
B. Emerson enhancement effect: the rate of photosynthesis when red and far-red light are given
together is greater than the sum of the rates when they are given apart.
The enhancement effect provided proof that photosynthesis is carried out by 2 photochemical systems
working in tandem but slightly different optima.
2 photosystems working in series : 2 physically and chemically different, each w/ own chlorophyll
antenna pigments and reaction center. Both are liked by electron transport chain.
PS II 690nm absorption maxima, poor absorption of far red (P680 reaction center), in grana
lamellae
PS I 700nm absorption maxima (P700 reaction center), in stroma lamellae
The Z scheme (zig zag scheme)
Red light is absorbed by PSII producing strong oxidant and weak reductant.
Far red light is absorbed by PSI and produces strong reductant and weak oxidant.
The strong oxidant generated by PSII oxidizes water while the strong reductant produced by PSI
reduces NADP+.
The reductant produced by PSII re-reduces oxidant produced by PSI.
Fig 7.16 Schematic picture of overall organization of chloroplast membranes
Chloroplast is surrounded by inner and outer membranes (envelopes, lipid bilayer).
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The stroma is the region of the chloroplast thats inside inner membrane and surrounds thylakoid
membranes. It contains enzymes that catalyze carbon fixation and other biosynthetic pathways.
Thylakoids contain all chlorophyll.
The thylakoid membranes are highly folded and are stacked (grana lamellae) and they form
one/few interconnected membrane systems. The exposed membranes where stacking is absent are
stroma lamellae.
Chloroplast also contains own DNA and RNA.
Fig 7.17 Integral membrane proteins of thylakoids
Many proteins essential to photosynthesis are found in thylakoid membrane such as the reaction
centers, antenna pigment protein complexes, and most electron carrier proteins. Thylakoid membrane
proteins have one region pointing toward stromal side of membrane and another oriented toward
interior portion of thylakoid (lumen).
Fig 7.18 4 major protein complexes
(1) PSII is located in grana lamellae. (2) PSI & (3) ATP synthase located in stroma lamellae. (4)
Cytochrome b6f complexes are evenly distributed. All are in vectorial arrangement.
This lateral separation of two photosystems requires electrons and protons produced by PSII to be
transported considerable distance before they can be acted on by PSI and ATP coupling enzyme.
Plastocyanin (thylakoid lumen) and plastohydroquinone (PQH2) located in thylakoid membrane are 2
mobile electron carriers.
In PSII, the oxidation of 2 water molecules produces 4 electrons, 4 protons, and a single O2.
The protons produced by this oxidation need to diffuse to stroma region where ATP is synthesized.
The role of this large separation between the 2 photosystems is not clear but is thought to improve
energy efficiency distribution between the 2 photosystems. The spatial separation btw PS indicates
that strict 1:1 stoichiometery btw PS isnt needed. There is excess of PSII in chloroplasts w/ PSII:PSI
1.5:1 but this can change when plants are grown in different light conditions. Cyanobacteria usually
have PSI >PSII.
Non O2 evolving (anoxygenic) organisms contain only a single PS similar to either PSI or PSII.
The structure of purple evolving bacteria is similar in many ways to that in PSII from O2 evolving
organisms (evolutionary relatedness).
Reaction centers from anoxygenic green sulfur bacteria and heliobacteria similar to PSI. (evol related)
Antenna complexes: Although reaction centers seem to be similar even in distantly related
organisms, antenna systems of different photosynthetic organisms are varied. The variety of antenna
complexes reflects evolutionary adaptation to diverse environments & need to balance energy inputs
to 2 photosystems.
Size and molecular structure varies (all associated w/ photosynthetic membrane).
Energy transfer in antenna complexes is very efficient (95-99% of photons absorbed have their energy
transferred to reaction center)
Energy transfer is physical phenomenon, electron transfer involves chemical changes in molecules
(produces reduced or oxidized species).
In all eukaryotic photosynthetic organisms that contain both chlorophyll a & b, the most abundant
antenna proteins are members of large family of structurally related proteins.
-LHCII: Some of the proteins are associated only w/ PSII and are called light-harvesting complex
II proteins.
-LHCI: Other proteins are associated w/ PSI. structure of LHCI is similar to that of LHCII (3
αhelical regions binding to 14 chlorophyll a & b, and carotenoids).
-antennae complexes are also known as chlorophyll a/b antenna proteins.
Fig 7.19 Funneling of excitation from antenna system to reaction center
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Description
Photosynthesis (chapter 7, 8, 9) Thylakoids (H20 is oxidized): H20 + light energy O2 + ATP + NADPH Stroma (carbon fixation, C02 is reduced): CO2 + ATP + NADPH (CH2O) = C02 + H20 (CH20) + O2 keq= 10 -500 (light driven redox process) Hill reaction: thylakoids were isolated & given light. O2 was released and reduction of Fe happened 3+ 2+ rather than C02 reduction. 4Fe + 2H2O 4Fe + O2 + 4H+ Artificial electron acceptor showed how photosynthesis & respiration worked Light has electric and magnetic field components (electromagnetic). Energy moves in wave w defined wavelength and frequency. Energy moves as particle in packets of energy called photons (quantum). Energy of photon is inversely related to its wavelength. Electromagnetic spectrum: shows type of radiation , F, E (gamma, xrays) , F, E (radio waves) The visible spectrum can be utilized and absorbed by plants (= 400-700nm) Fig 7.3 solar spectrum and relation to absorption of chlorophyll of light energy. - Top curve is energy of output of sun as function of wavelength - Second curve is energy that strikes Earth surface. It is less bc some energy is absorbed by water vapor in atmosphere. - Third curve is absorption spectrum of chlorophyll which strongly absorbs in blue (430nm) and red (660nm) spectrum portions. When a photon of light is absorbed by chlorophyll pigment, the electron distribution is altered, and some electrons move away from nucleus. The chlorophyll molecule then goesback to ground state. Chl + photon (ground state) Chl* (excited state; altered e- distribution) 4 routes to dissipate energy from lowest excited state: Note: photosynthesis doesnt use 1&2, 3&4 need to occur rapidly to compete w 1&2 1. Heat 2. Fluorescence: Re-emit photon of longer i.e. less energy bc some of energy already lost as heat 3. Resonance transfer: energy transfer to another molecule, usually chlorophyll & its physical energy transfer 4. Photochemistry: electron transfer from donor to acceptor Fig 7.5: light absorption and emission by chlorophyll. Blue light (E photon,) Red light (E photon,) - All absorption of light can lead to at least the lowest excitable state which drives photochemical and resonance transfer. The highest excited state is not very useful so it quickly dissipates to the lowest excited state. Red light is just as good at driving photosynthesis as blue light. Chlorophyll a & b have small structural differences but in general are a porphyrin-like ring structure w central Mg and hydrophobic tail that allows for effective interaction w hydrophobic bilayer of thylakoid membrane. Chlorophyll strongly absorbs in blue (430nm) and red (660nm) absorption spectrum. Carotenoids are orange, accessory pigments for photosynthesis that absorb 400-500nm of light and transfer them to chlorophyll for photosynthesis. Carotenoids use that chlorophyll isnt able to use. They have a photoprotective role to protect organism from damage caused by light. Chlorophyll B are different bc 1 functional group on ring is different- different absorption spectrum. Bacteriochlorophyll a & bilin pigments are found in photosynthetic bacteria. Common to all is the complex ring structure. Fig 7.7 Absorption spectra of photosynthetic pigments dissolved in nonpolar solvents. However, the true absorption spectrum of the pigments is dependent on membranes environment. Pigments shown www.notesolution.com in this figure are Curve 1= bacteriochlorophyll a, Curve 2=chlorophyll a, Curve 3=chlorophyll b, Curve 4=phycoerythrobilin, Curve 5=B carotene. Fig 7.8 Absorption spectra compared w action spectra Absorption spectra: effectiveness of chlorophyll molecule to absorb different light . Action spectra: effectiveness of different light to drive some biological process(here it is O2 evolution) - There is a very close match btw absorption and action spectra. To measure O2 concentration, light was shined onto the alga (spirogyra)s chloroplast. Aerotactic bacteria aggregated at O2 regions (in spectrum region where chlorophyll absorbed most effectively Blue, Red). It was first indication of effectiveness of light absorbed by accessory pigments in driving photosynthesis. Fig 7.11 Relationship of oxygen production to flash energy Chlorella- short light flashes of different intensity, O2 release was measured, O2 release saturated at high intensity. They thought that 1chlorophyll would yield 1 O2. However, the finding was that 2500 chlorophyll molecules would release 1 O2 at saturating energies. This was done by quantifying chlorophyll amount and O2 amount and forming a ratio. Reasons for 1 O22500 chlorophylls: 1. Hundreds of chlorophylls absorb light and transfer energy via resonance transfer until its all funneled to 1 chlorophyll molecule (reaction center). Electron transfer then happens. 2. Each reaction center needs to operate 4 times to generate 1 O2. 3. 2 different types of reaction centers (photosystems) working in series Fig 7.10 Basic concept of energy transfer during photosynthesis 2 stages: (1) Physical transfer: many chlorophyll pigments collect light and transfer it via resonance transfer to reaction center. (2) chemical reactions store some of energy in reaction center by transferring e- to an acceptor mol. An e- donor then reduces the chlorophyll reaction center again. A. Red drop effect not consistent w findings. Quantum yield = # of photochemical produces total # of quanta absorbed Far red light (> 680nm) is inefficient at driving photosynthesis. Quantum yield of O2 evolution falls off drastically for far-red light of wavelengths > 680n meaning that red light alone isnt enough at driving photosynthesis. The dip near 500nm reflects the lower efficiency of photosynthesis using light absorbed by accessory pigments (carotenoids). B. Emerson enhancement effect: the rate of photosynthesis when red and far-red light are given together is greater than the sum of the rates when they are given apart. The enhancement effect provided proof that photosynthesis is carried out by 2 photochemical systems working in tandem but slightly different optima. 2 photosystems working in series: 2 physically and chemically different, each w own chlorophyll antenna pigments and reaction center. Both are liked by electron transport chain. PS II 690nm absorption maxima, poor absorption of far red (P680 reaction center), in grana lamellae PS I 700nm absorption maxima (P700 reaction center), in stroma lamellae The Z scheme (zig zag scheme) Red light is absorbed by PSII producing strong oxidant and weak reductant. Far red light is absorbed by PSI and produces strong reductant and weak oxidant. The strong oxidant generated by PSII oxidizes water while the strong reductant produced by PSI reduces NADP+. The reductant produced by PSII re-reduces oxidant produced by PSI. Fig 7.16 Schematic picture of overall organization of chloroplast membranes Chloroplast is surrounded by inner and outer membranes (envelopes, lipid bilayer). www.notesolution.com
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