historicsweetsballroom.com.edu); biologic Department, college of St. Benedict/St. John"s University, Collegeville, MN 56321

AUTOTROPHIC NUTRITION(or, Life is a photochemicalphenomenon)

I.Overview that photosynthesis: Photosynthesiscan be characterized as the light-driven synthetic of carbohydrate. Remind theequation for this reaction:

CO2 + H2O +light + chloroplasts �(CH20)n + O2

From this an easy equation we have the right to make someelegant conclusions:A. Photosynthesis is a oxidization reaction

CO2 is reduced to a carbohydrate <(CH20)n > Water is oxidized (to oxygen) Water supplies the electrons for the reduction of carbon dioxide; water is cleaved in the procedure yielding oxygen together a byproduct. Light offers the power for the reduction. Light basically splits water (photolysis) to yield electrons and also protons because that photosynthesis. B. Photosynthesis is an power conversion process. Throughout photosynthesis, light energy is ultimately converted come chemical energy (carbohydrate). In a large sense, that is an instance of the first Law the Thermodynamics (recall that power cannot be created nor destroyed, yet it have the right to be readjusted from one kind to another).C. Black BOX an overview model for photosynthesis. Diagram detailed in class. This version shows the there room three major energy conversions during photosynthesis:

radiant energy (sunlight) � electric energy (passage of electrons via a collection of carrier) � chemical power (ATP, NADPH; unstable) � chemical energy (carbohydrates; stable). The very first two switch are component of the light-dependent reaction that happen in the thylakoid membranes of the chloroplast; the critical step refers to the light-independent reaction (Calvin cycle) that happen in the stroma.

You are watching: Why are leaves thin and flat

II. Leaves - the major photosynthetic organs Leaves space perfect solar collectors. This organs are wide and flat to enable forefficient irradiate harvest. The leaves are vast to maximize surface area for light harvestand they room thin because light cannot penetrate too deeply into the leaf (the lot oflight decreases exponentially with distance). Together an aside, return the majority of lightis absorbed near the sheet surface, in some situations, tree tissues have the right to act choose fiber opticcables that have the right to funnel part light deeply right into the tree body.

even within the thin leaf, many chloroplasts are uncovered in the upper layer the cells, thepalisade layer, which is a organization layer simply beneath the top epidermis of the leaf. Thismakes "sense" since these cells get the best amount the lightof any region in the leaf.

Leaves dual as a method to exchange photosynthesis gases (take increase carbon dioxide andget rid of oxygen) with the environment. Leaves have pores in the surface (stomata) thatregulate the entry/exit that gases and prevent the ns of too much water.

The spongy layer of the leaf acts like a "lung" increasing the internalsurface area and provides for much more rapid diffusion within the leaf. Note again the leavesare slim - this stays clear of the need for lung or other type of pump to relocate gases. Sincediffusion prices are inversely regarded distance, an easy diffusion deserve to account for gasmovements into/out of a leaf. An included advantage the having large leaves because that light harvestis the they provide lots of surface ar area for absorption the carbon dioxide.

Veins and also vascular tissue supply the leaf through water (xylem) and transport the endproducts to other parts that the plant (phloem).

III. Chloroplasts - specializedorganelles that bring out the procedure of photosynthesis

A. Structure. psychic the cell unit? to jog her memory, reread the cellchapter. Terms that you should understand are optical membrane (or lamellae), inter-membranespace, twin membrane, stroma, granum (grana).

B. Chemistry.Chloroplasts contain....

1. Assorted Goodies: DNA - circular loop, similar to a bacterial chromosome though much smaller - only sufficient nucleotides (ca. 120-160 kilobases) to password for about 120 proteins; RNA; ribosomes; protein - some are encoded by the genes in the nucleus, others by the genes in the chloroplast DNA. For example, rubisco, critical enzyme, has actually 2 various subunits, one coded by every source. The nuclear gene are vital for chloroplastic function, however the turning back is not true2. Pigments: These comprise about7% of the chloroplast. A pigment is any molecule with a shade that absorbs light. Theseoccur in the thylakoids since they are very hydrophobic (fat-soluble).There space twomajor groups of pigments in higher plants - chlorophylls and also carotenoids/xanthophylls.

Chlorophylls - green; look choose a tennis racket. The head of the racket is a ring system based on the structure of heme (a kind of porphyrin). Magnesium is inserted in the ring. Chlorophyll also has a lengthy (C-20) hydrocarbon tail. The tail is essential for placing the molecule in the membrane. The communication of the chlorophyll through the membrane is non-covalent and is important because it ultimately determines the physics properties that the chlorophyll. Carotene/xanthophylls - both are large hydrophobic molecule (C-40). Carotenes are hydrocarbons; xanthophylls space oxygenated. These pigments are orange pr yellow in color.

3. Electron transfer Complexes: There room four significant complexes (groups the proteins, colours andelectron carriers) in the chloroplast membrane (thylakoids). This complexes arephysically separate from one another and can be isolated indigenous the chloroplastic bybiochemical techniques (electrophoresis and also ultra centrifugation). This complexes room (don"tmemorize the individual contents - merely appreciate the diversity and complexity):

(a) Photosystem II (PSII) facility 6 integral proteins - coded by the chloroplast genome three peripheral proteins - coded by nuclear genome; they tie Ca2+ and also Cl- 4 MN2+ LHCII - light harvesting pigment facility associated through PSII. That is consisted of of: (1) about 250 chlorophyll a & b, in around equal amounts; (2) xanthophyll; (3) proteins - every pigment is linked with protein. The protein is coded by the atom genome P680 reaction facility � a distinct chlorophyll a, best red irradiate absorption at 680nm; it might actually be two chlorophyll a molecules; this is the chlorophyll the "looses" electrons (b) Cytochrome b/f facility cytochrome b cytochrome f other proteins including a non-heme iron-sulfur protein (2Fe-2 S) (c) Photosystem ns (PSI) complicated 11 polypeptides 50-100 chl a electron carriers LHCI - contains around 100 chlorophylls; 4:1 proportion of chl a: chl b.; the protein is encoded by nuclear genome P700 reaction facility � unique chlorophyll a that absorbs irradiate in the red an ar at 700 nm (d) ATP synthase/Coupling Factor complicated stalk - CF0 head - CF1 nine polypeptides (some nuclear, some chloroplastic) basically the same as the one in the mitochondrion III. From photons come electrons

A. Nature of irradiate

component of the electromagnetic spectrum - radiation emitted bysun. acts as discrete particles (called photons) travels as waves wavelength- street between any kind of two crests (or troughs). Symbolized by lambda (λ); frequency - number of waves happen a allude in one second (ν). Frequency isinversely related to wavelength ν = c/λ where c = speed of light (3 x 1010cm sec-1). (not ~ above exam) The power of a photon is a quantum.

B. I beg your pardon photons are necessary inphotosynthesis? run an activity spectrum (graph that a physiologicalprocess vs. Wavelength).

****refer to action spectrum ofphotosynthesis****

Conclusion: radiations between 400-700 nm arephotosynthetically energetic (termed PAR). Specifics red (600�s) and also blue(400�s) light is specifically important.

C. Photons should be absorbed to be supplied in aphotochemical reaction. So, which molecule absorb the red and also bluelight? operation an absorption spectrum of potential colors candidates (plotof irradiate absorption vs. Wavelength) and compare it to the action spectrum.

****refer to absorption spectrum ofphotosynthetic pigments.****

Chlorophyll a & b absorb lightin red and blue areas of the clearly shows spectrum. Note that their absorptionspectrum matches the action spectrum the photosynthesis perfectly and also hence,strongly implicates (though doesn�t prove) castle in the process. (Subsequentwork has shown the chlorophylls to be the major photosynthetic pigments).

D. Duh! In truth it wasn"t crucial to prepare activity andabsorption spectra to learn that red and also blue irradiate was important forphotosynthesis. Because leaves space green, it way that lock don"t absorbthe green wavelengths of irradiate in the visible spectrum however absorb the remainder(blue and reds). Thus, these are the ones easily accessible for photosynthesis. As an example, if friend look with a pair of red sunglasses the human being looks rosy. This is since the colors in the lens absorbs every wavelengths the light other than red which deserve to then it is in transmitted thru the lens to her eye.

E. Amount vs. Top quality (not top top exam) irradiate quality describes the wavelengths of light that room important. Photosynthetically active radiations (PAR) range from 400 - 700 nm v peaks in the red and also blue.Light quantity. Refers to the quantity of light (PAR) received; devices of mol m-2 s-1 , dubbed the photon fluence rate; or devices of energy, J m-2 s-1.F. What happens when chlorophyll absorbs light? The chlorophyll molecule becomes excited (this takes only 10-15sec = femptosec) and an electron moves to one outer energy level. CHL (groundstate) �CHL* (excited state)

Blue irradiate excites anelectron to a higher energy level than red light. Imagine the "bell ringerat a carnival." electron don�t stay excited lengthy (10-9 sec) - they can:

go back to the ground and release energy as warm (thermal deactivation); return to ground state and also release energy as light (fluorescence); the power may be transferred to one more molecule, sort of like hitting swimming pool balls (resonance transfer). Example: CHL1* + CHL2 → CHL1 + CHL2* be supplied in a photochemical reaction (passed on to an electron carrier). Example: CHL* + electron carrier(ox) → CHL+ + electron carrier(red)-

G. Why wake up electrons? The ultimate objective of interesting electrons from chlorophyllis to administer the power needed to deliver electrons from water to NADP+.This is necessary since water has a lower power state 보다 NADP+ -thus, the only way get electrons from water to NADP+ is to very first excite castle toa high power state therefore they can flow downhill to NADP+.

IV. The Z-Scheme (Or, theLight-Dependent Reactions; Or, Non-cyclic photophosphorylation)

A. Overview. during thelight-dependent reactions of photosynthesis, electrons are transferred fromwater to NADP+. This reaction is shown asfollows:H2O �NADP+

In the thylakoid, three ofthe complexes mentioned over (III.B.3.a) are responsible for carrying the electronsfrom water to NADP+.These room Photosystem II (PSII), the cytochrome b/f complicated (cyt b/f), andPhotosystem ns (PSI). After electron are gotten rid of from water, they aresequentially shuttled native PSII come the cyto b/f complicated to PSI and also then finallyto NADP+.Thus:

H2O �PSII �Cytb/f �PSI �NADP+

since the three complexes arephysically separated indigenous one one more in the optical membrane membrane, there need to be a method to transferelectrons in between the complexes. A mobile form of plastoquinone (PQ) transferselectrons from PSII come cyt b/f. A copper-containing protein, plastocyanin (PC),transfers electron from the cytochrome b-f facility to PSI. Thus, the reactionsequence is modified together follows:

H2O �PSII �PQ �Cytb/f �PC �PSI �NADP+

The transport of electrons from PSI come NADP+requires a dissolve carrier uncovered in the stroma, ferredoxin (Fd). For this reason ourrevised equation:

H2O �PSII �PQ �Cytb/f �PC �PSI �Fd �NADP+

The move of electron from water come PSIIinvolves one "oxygen evolving complex" (OEC) i m sorry is a component of PSIIandrich in chloride and manganese ions. Thus,

H2O �OEC �PSII �PQ �Cytb/f �PC �PSI �Fd �NADP+

B. Origin of the name, Z Scheme. Obtained from the arrangement of materials with regard toenergy potential. But, why don�t we contact it the N-scheme?

V. PhotophosphorylationLiteral translation - "the light thrust synthesis that ATP"Occurs by the same mechanism, "Chemiosmotic Hypothesis", that occurs throughout ATP synthetic in the mitochondriathe passage of electrons v the carrier complexes results in the movement of electrons from the stroma right into the intermembrane space.pH gradient is generated across the membrane, the stoma pH is ca. 8 if the lumen is ca. 5.This happens since the thylakoid, prefer the within membrane of the mitochondrion, is impermeable come protonsthe pH gradient gives the energy for the synthetic of ATPATP is synthesized by one ATPase associated with the CF complex; andprotons escaping with the channel cd driver ATP synthesis something favor water transforming a mill.Evidence:lots! a pH gradient exists in the chloroplast. Discharging the gradient v buffers avoids ATP synthesis; uncouplers like DNP "poke holes" in the optical membrane making that "leaky" and also discharging the gradient avoiding ATP synthesis. Note that this doesn�t avoid electron flow - in fact, the usually rises the rate. VI. The final frontier - Calvin-Benson bike or photosynthetic CarbonReductionA. General:

dubbed "dark reactions" since the reaction don�t require light - However, keep in mind that these reactions have the right to (and do) take place in the light. In one feeling they deserve to be considered "light dependent" since they require the ATP and also NADPH generated during the Z scheme. dubbed the Calvin bicycle - ~ the fellow and his colleagues who settled most of the reactions. If you had done it, friend too, would own a Nobel Prize wake up in the stroma there are four significant steps: continuous � palliation � rearrangement � charging (note this is slightly various than the text)

B. Carbon dioxide fixation- carbon dioxide is solved (trapped, bound) to form an organic compound (phosphoglycericacid, PGA) carbon dioxide binding to RuBP (ribulose bisphosphate; C5) to kind 2 molecules of PGA (C3) an initial product that carbon continuous is PGA (Calvin�s experiments) catalyzed by the enzyme ribulose bisphosphate carboxylase (rubisco). Rubisco is the many abundant protein top top earth; it renders up 50% of leaf proteinC. Reduction- action in i beg your pardon the "temporary" chemistry (ATP) and also reducing (NADPH)energy the were produced in the light-dependent reactions are provided to reducethe PGA native an mountain to a carbonyl (glyceraldehyde 3-phosphate; abbreviation G3Por GAP) PGA is lessened to G3P this is a two-step reaction succession first, PGA is phosphorylated with ATP come 1,3-bisphosophoglycerate which is subsequently decreased to G3P (note a phosphate is lost throughout this reaction). NADPH offers the electrons because that the reduction energy requirements - in ~ this suggest in the cycle, for each carbon dioxide fixed, 2 ATP and two NADPH are compelled (one for each that the two PGA�s)C. Rearrangement- facility series of reaction that result in the network removal the a C3carbohydrate native the cycle and the production of the precursor to the startingmaterial: see overhead and diagram in text for details the cycle have to turn 3 times because that the production of one net three carbons sugar the end product that the bike is ribulose-5-P (RuP)D. Charging- the original starting material (RuBP) is created using the chemistry potential(ATP) generated throughout the light-dependent reactions. ATP converts ribulose-5-P come RuBP ATP comes from the Z schemeE. Summary:the continuous of 1 carbon dioxide requires: 3 ATP and 2 NADPH.

VII. C3 Plants. Plants the exhibit the form of photosynthetic carbonreduction that us described above are termed C3 plants. In various other words, first product of carbon dioxide fixation is a 3-carbon link (PGA). Thus,when radioactively labeled carbon dioxide is fed to a plant, the an initial placethat it reflects up is PGA.

(the remainder of the notes are not spanned on the exam)VIII. Photorespiration- Light engendered production that carbon dioxide in the presence of oxygen

not associated with mitochondrial respiration requires light not accompanied by ATP synthesis wastes power (i.e., ATP, NADPH)

A. The trouble - Rubisco. Unlike many enzymes, rubisco is no substrate particular - italso has an oxygenase function. In addition to its typical substrate (carbondioxide) rubisco also binds oxygen come RuBP. Back rubisco has a higheraffinity for binding carbon dioxide (Km = 9 uM), if sufficient oxygen is present, itwill act as a competitive inhibitor (the km for oxygen is 535 uM).B. The reaction catalytic analysis by ribulosebisphosphate carboxylase/ oxygenase. As soon as rubisco binding oxygen to RuBP, the RuBP is essentiallysplit in fifty percent to a 3 carbon piece and a 2 carbon fragment according to thefollowing reaction: RuBP + oxygen �PGA (C3) + phosphoglycolate (C2)

Compare this come the regular reaction:RuBP + oxygen �2 PGA (C3)

Thus, rubisco has oxygenase activity as fine asa carboxylase.

C. What identify which procedure will occur? Oxygenase task occurs during periods of activephotosynthesis when: carbon dioxide levels are low; and oxygen levels are high - due to the activity of PSII; high irradiate intensity. The proportion of /ultimately identify the product of the rubisco reaction.

if = high; then it favors regular Calvin bike if = low; then it favors oxygenase activity

IX. Photosynthesis carbon oxidation (PCO),or, Glycolate Cycle. The function of this pathway is come metabolize and also reclaim thecarbon in phosphoglycolate

A. Rundown of the significant steps: The commodities of rubisco oxygenase activity are phosphoglycolate (C2) and PGA (C3); PGA start the Calvin cycle as normal; Phosphoglycolate is further metabolized in the peroxisome and also mitochondria and also some (75%) the the carbon in PGA is at some point reclaimed. The various other carbons atoms space released as carbon dioxide native the mitochondria (not linked with to move respiration) and also hence the factor this is called a "respiration". Keep in mind that the cycle is oxidative (redox reactions occur) and also takes ar in 3 organelles;B. Why perform plant photorespire? indigenous a Darwinian perspective, we�d intend that this processwould have been selected against. However, the truth that so countless plants perform it,suggests that it may have actually an unappreciated function. Possibilities include: (a)salvage the carbon lost during rubisco oxygenase action; (b) device to helpprevent devastation by excess light.

X. C4 Photosynthesis, or, how maize avoidsphotorespiration. plants that protect against photorespiration have a unique modificationof photosynthesis. They are referred to as C4 plants because the first product the carbondioxide permanent is a 4-carbon compound, no PGA as it is in C3 plants.

Examples: over there are numerous plants that have actually thisspecialized modification. Uncovered in many different and unrelated groups of plantswhich suggests that it apparently developed independently number of times. Evenwithin a genus, part members can be C4 rather C3.

C4 photosynthesis is commonin grasses favor maize, sorghum, crabgrass. But, no all grasses room C4;for example, Kentucky blue grass (Poa pratensis; common lawn grass) isC3.

A. Exactly how do C4 plants protect against photorespiration? The answer is ingenious - C4 plants different the website of oxygenproduction (PSII) from rubisco (Calvin cycle). However how? PSII and rubisco areplaced in different: Cells. In common C3 plants the chloroplast are distributed throughout the mesophyll. Usually there is a well-defined palisade and spongy layer. In contrast, C4"s have a much more or less uniform mesophyll layer v a well-developed bundle sheath approximately each vein. This is dubbed Kranz anatomy, due to the fact that the bundle sheaths shows up like a wreath surrounding the vein. In C4 plants, the Calvin cycle activity occurs mostly in the bundle sheath cells, whereas PSII activity occurs in the mesophyll cells. Chloroplasts. The chloroplastic of C4 are of 2 forms. Bundle sheath cell (BSC) chloroplasts room agranal and have tiny PSII activity; but, they do have hi PSI activity. The mesophyll cabinet (MC) chloroplastic have common granal stacking, however low rubisco activity. Thus, most carbon permanent (carbohydrate production) occurs in the BSC. Smart, eh? B. Carbon Shuttle- due to the fact that C4 plants have separated the Calvin bike PSII, there need to be amechanism to gain carbon dioxide into the BSC since: there is fairly slow diffusion come deep, inner regions that the leaf, specifically considering; the ambient level of carbon dioxide is low. In order to deal with this problem, tree requireda system to: solve carbon dioxide in areas of the leaf wherein it occurs in high concentration (i.e., MC). The enzyme that catalyzes this reaction is phosphoenolpyruvate carboxylase (PEPcase). This enzyme binds carbon dioxide (actually bicarbonate) come PEP to form oxaloacetate (reaction diagram). This reaction occurs in the cytoplasm. Note that OAA is a C4 compound. Hence these tree are called C4 - since the an initial product that carbon permanent is a 4 carbon compound. Transfer the solved carbon dioxide (which is in the kind of a C4 compound favor malate or aspartate) from the MC come the BSC. The C4 molecule is converted to another C4 link that, in turn, migrates to the BSC where it is decarboxylated and used in the Calvin cycle. The "leftover" C3 shuttles ago to the MC to choose up one more carbon dioxide and also repeat the process. C. Basic scheme- ~ above overhead, covered in class

D. Advantages of C4 metabolism. Plants that exhibit this kind of photosynthesis room characteristic the hot,tropical atmospheres that have actually a high light fluence. The benefit of C4 inthese scenarios is the C4 metabolism: prevents the photorespiratory loss of carbon improves the water use performance of the plants results in higher rates the photosynthesis in ~ high temperatures enhances the performance of nitrogen use (because C3 require many rubisco) XI. Crassulacean mountain Metabolism -CAM plants

A. Beginning of the name. Crassulacean refers to the Stonecrop family (Crassulaceae)and connected succulents in i beg your pardon this process is common. Come date, plants in morethan 18 different families including Cactaceae (Cactus family) and also Bromeliaceae(Pineapple family) have actually been shown to lug out video camer metabolism. Mountain isderived native the observation that this plants accumulate big amounts oforganic acids in the dark.

plants with electronic came metabolismtypically evolved in dry, hot, high light environments. This is greatly amechanism to conserve water. Recall the photosynthesis/transpiration compromise(paradox)? plants in dry atmospheres can�t bought to compromise - they loosetoo much water opening their stomates during the day. Video camer plants fixed thisproblem by opened up the stomates in ~ night to obtain carbon dioxide. Thisstrategy is just the turning back of "normal" plants. But, this presentsanother problem - ATP & NAPDH, i beg your pardon are products of the light dependentreactions, space not easily accessible when the carbon dioxide is fixed. The equipment tothis difficulty was to store the carbon dioxide during the night till ATP andNADPH were obtainable the following day. Thus, there is a temporal separation ofinitial carbon permanent via PEPcase and the Calvin cycle. (C4 plants have aspatial separation).

See more:  Tr A Line That Intersects Two Or More Coplanar Lines At Different Points

B. PEPcase. This is the early enzyme that fixes carbon dioxide. Theproduct is ultimately malate, an essential acid, which accumulates in the vacuole throughout the night(hence the "acid" term).

C. Sequence of events. Night �stomates open up �nocturnal transpiration (lower 보다 diurnal) and also carbon permanent by PEPcase �OAA produced �reduced with NADPH to malate �shuttled right into vacuole �acid content of vacuole boosts �starch depleted to administer PEP because that carboxylation �day �stomates nearby �transpiration reduced �acid content decreases �malate decarboxylated to carry out carbon dioxide because that Calvin bicycle �starch content increases