Photosynthesis – Part IISpring 2013 - Althoff Reference: Mader & Windelspecht Ch. 7)

Lec08

• Plants as Solar Energy Converters

• Plants as Carbon Dioxide Fixers

Solar Energy & Wavelengths

• There are 7 basic categories of radiant (aka solar) energy in the electromagnetic spectrum:

gamma raysx-raysUV___________________infraredmicrowavesradiowaves

• Visible spectrum: 380-750 nm (nanometers)

Visible Light

• Wavelengths different for ______________

Increasing wavelength

Increasing ENERGY

Absorption Spectrum for __________________ Pigments

chlorophyll a

chlorophyll b

carotenoids

For the record…

• Notice that the different photosynthetic pigments have different absorption spectrums

• Chlorophyll a and b have a wider “_________” range than carotenoids….as carotenoids do not have any absorption beyond approximately 500 nm.

• Because of the wider absorption spectrum, chlorophyll a and b play “THE” ____________ roles in photosynthesis…

• Carotenoids play an _____________ role.

Non-cyclicpathway

Electron flowin light reactions

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4a

Electron Flow…starting with the light reactions

• ______________________– the route electrons usually travel during the ___________________.

• Starts with “Photosystem II” (although it happens essentially first).

• Pigments absorb solar energy, then pass to other pigments until it is concentrated in a particular pair of ____________________ molecules—known as the “______________________”

• Electrons (e-) become so energized that they escape the reaction center and move to nearby _________ _________________

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Electron Flow…from light reaction to Calvin cycle reactions…

• Water splits, releasing ____ into the atmosphere

• The H+ stays in the ________________ and contribute to the formation of the H+ gradient.

• Electron acceptor sends __________ electrons down an electron transport chain.

• Combined with ATP synthase complexes, ATP production occurs…which is then….

• Used by the ______________________ in the _________ to reduce CO2 to a carbohydrate

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simultaneously on the Calvin cycle reactions side…

• Energized electrons leave the reaction center, to the electron receptor…

• to merge with NADP+ and H+ to form ________. This is on the ____________________ side…2 electrons are accepted here.

• In the Calvin cycle reactions, the NADPH along with the ATP that came from the light reaction side _________ CO2 to CH2O (aka a carbohydrate)

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Organization of the Thylakoid Membrane• Photosynthesis II – pigment

complex and electron-acceptor molecules; releases O2

• Electron transport chain carries electrons from PS II to PS I via _______________. H+ pumped from stroma into thylakoid space.

• Photosynthesis I – pigment complex and electron acceptor molecules reduces NADP+ to NADPH

• ________________ complex is an enzyme that joins ADP + P to make ATP

ATP Production• Thylakoid space acts as a ____________ for many H+. • As water is _____________, two H+ remain in the

thylakoid space.

• Result: __________ in thylakoid space than in the stroma…then flow of H + to from _____________ concentration provides kinetic energy that allows ATP synthase complex enzyme to join ADP + P. This method of producing ATP is called chemiosmosis—what we looked before (Chapter 6)

• Summarized in next slide

chemiosmosis

PS II

PS I

Plants as Carbon Dioxide Fixers• Calvin cycle discovered by ______________ and

colleagues, used radioactive isotope 14C as a tracer to “follow around” the reactions.

• Photosynthesis uses CO2 from the ______________ to produce carbohydrates.

• Question…how does the CO2 get into atmosphere in the first place??? Answer: when ____________ take in O2 they ______ CO2. Of course, the CO2 is produced by cellular respiration (the details starting after the next exam).

• Carbon dioxide (CO2) fixation is the first step of the Calvin cycle. As shown in the next slide

________________Reactions – details

these ATP produced bylight reactions

these ATP & NADPHproduced bylight reactions

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The Calvin cycle reactions• ___________– 1st step – molecule of carbon dioxide

from atmosphere is attached to _____ (ribulose-1, 5-bisphosphate), a 5-carbon molecule. The result is a 6-carbon molecule, which splits into two __________ __________. Enzyme that speeds up this reaction is RuBP carboxylase—a protein that makes up 20-50% of the content of chloroplasts. Large amount necessary because, compared to other enzymes it is rather slow acting.

• ______________– 2nd step – first 3-carbon molecule is called 3PG (3-phosphoglycerate). Each of 2 3PG molecules undergoes reduction to make ____ (glyceraldehyde-3-phosphate)—in 2 steps

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The Calvin cycle reactions…con’t

• _________________ – 3rd step – in diagram on previous slide, notice Calvin cycle reactions are multiplied by 3 because it takes three turns of the Calvin cycle to allow one G3P to exit….

• Results in 5 molecules of GCP per every 3 turns to reform 3 molecules of RuBP…and the cycle continues.

• The reaction uses some of the ATP produced from light reactions.

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Importance of the Calvin cycle

• _____ is a product of the Calvin cycle – it can be converted to other molecules the plant needs

• ____________________ is among the organic molecules that result from GCP metabolism

• This is of interest because glucose is “the” molecule that plants and animals most often _____________ to produce ATP molecules required to meet their energy needs.

• Examine next slide to see the _______ of G3P.

Fate of G3P

Glucose phosphateFatty acid synthesis

Amino acid synthesis

+ Fructose phosphate

+ Sucrose

(in leaves, fruits and seeds)

Starch (in roots and seeds)

Cellulose(in trunks, roots and branches)