Photosynthesis – Part II Spring Althoff Reference: Mader & Windelspecht Ch. 7) Lec 08 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 rays x-rays UV ___________________ infrared microwaves radiowaves Visible spectrum: 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-cyclic pathway Electron flow in light reactions a 3a 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 _________ _________________ 1 2

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 CO 2 to a carbohydrate 3 4

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 _________ CO 2 to CH 2 O (aka a carbohydrate) 2a 3a 4a

Organization of the Thylakoid Membrane Photosynthesis II – pigment complex and electron- acceptor molecules; releases O 2 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 14 C as a tracer to “follow around” the reactions. Photosynthesis uses CO 2 from the ______________ to produce carbohydrates. Question…how does the CO 2 get into atmosphere in the first place??? Answer: when ____________ take in O 2 they ______ CO 2. Of course, the CO 2 is produced by cellular respiration (the details starting after the next exam). Carbon dioxide (CO 2 ) fixation is the first step of the Calvin cycle. As shown in the next slide 

________________ Reactions – details these ATP produced by light reactions these ATP & NADPH produced by light reactions 1 2 3

The Calvin cycle reactions ___________– 1 st 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. ______________– 2 nd 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 1 2

The Calvin cycle reactions…con’t _________________ – 3 rd 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. 3

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 phosphate Fatty acid synthesis Amino acid synthesis + Fructose phosphate + Sucrose (in leaves, fruits and seeds) Starch (in roots and seeds) Cellulose (in trunks, roots and branches)