Photosynthesis I BIO 105 Cr.4
UW - L
Popular in General Biology
Popular in Biology
verified elite notetaker
This 4 page Class Notes was uploaded by MaKena Betler on Saturday October 31, 2015. The Class Notes belongs to BIO 105 Cr.4 at University of Wisconsin - La Crosse taught by a professor in Fall 2015. Since its upload, it has received 25 views. For similar materials see General Biology in Biology at University of Wisconsin - La Crosse.
Reviews for Photosynthesis I
Loved these! I'm a horrible notetaker so I'll be your #1 fan in this class
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 10/31/15
Lecture 21: Photosynthesis I Key Concept #1: Photosynthesis is the source of all the reduced carbon in the biosphere and all the O in the atmosphere. 2 o Producers bring energy and matter into the biosphere by fixing carbon ( CO 2 ) into carbohydrates (sugars, starch) o Autotrophs: produce complex organic molecules (glucose, starch) from simple inorganic molecules ( CO 2 H 2 ) o Photoautotrophs: transform radiant energy (sunlight) into chemical energy (ATP) to produce complex organic molecules (glucose, starch) o Producers store potential energy in the covalent bonds of the sugars, starch cellulose, etc. o Humans (heterotrophs) eat apples for the energy they contain in their starch molecules (through respiration) o Photosynthesis net reaction: 6CO 26H 0+2unlight→C H O6+612 6 2 o Overview of photosynthesis: Light excites electrons in chlorophyll, which are passed to NADP+ to make NADPH H 0 Electrons from 2 reduce chlorophyll back to its original form, making O2 In these steps, an electron transport mechanism like that of the mitochondria generates an H+ gradient across the thylakoid membrane, and ATP synthase (like in the mitochondria) harvests the gradient to make ATP Light independent reactions: Calvin Cycle: A metabolic pathway that uses ATP energy and electrons from NADPH to reduce CO 2 and produce sugars like glucose Occurs in the stoma Key Concept #2: The light reactions of photosynthesis generate ATP using a proton gradient and ATP synthase, just as in mitochondrial ATP synthesis. o If one molecule is being reduced: NADP+ to NADPH, another is being oxidized o The chlorophyll at the reaction center donated an electron and needs to get one back o H2O gets oxidized and serves as the electron donor: +¿+O 2 ¿ −¿+4H ¿ 2H O24e Respiration and catabolic pathways generally use NAD+/NADH Photosynthesis and anabolic pathways, generally use NADP+/NADPH o Glucose is the “start” of respiration metabolism and the “end” of photosynthesis o Respiration and photosynthesis are superficially reverse processes o Photosynthesis occurs within chloroplasts of mesophyll cells Stacks of thylakoid membranes within the chloroplast carry membrane protein complexes that carry onto photosynthesis Chloroplasts: endosymbiosis analogues to mitochondria Photosynthesis consists of: Light-driven reactions to generate ebergy Calvin Cycle to generate organic compounds o The light reactions The photosystem II: Chlorophyll electrons ( −¿ ) excited e by light reduce electron carrier PQ, −¿ from H O re- e 2 reduce chlorophyll, resulting in O2 −¿ As e¿ pass through cytochrome (Cyt.) and plastocyanin (Pc) to photosystem I, H+ pumped in cytochrome pumps H+ exactly like complex III in mitochondrial −¿ transport e Light re-excites −¿¿ in chlorophyll of photosystem I, e making them energetic enough reduce ferredoxin (Fd) and then NADP+ to make NADPH ATP synthase works just like the mitochondria o Chlorophyll is a natural pigment that absorbs photons of light: “True” chlorophylls are found only in cyanobacteria (and plastids) Bacteriochlorophylls found in proteobacteria (purple sulfur bacteria) Why do spectra differ? Small changes to the shape of the ring = large changes in the wavelengths of light absorbed. o Electromagnetic radiation is composed of photons whose energy is inversely proportional to wavelength o Phototrophic organisms are really “eating light” Just like with any ecosystem where multiple organisms are competing for the same resource evolution selects for those organisms that specialize a particular kind of “prey” o Carotenoids in leaves become apparent in fall o Photosynthetic life began in the seas, where light is sometimes hard to come by o Chlorophyll molecules transmit energy from excited electrons in the antenna complex to a reaction center ~300 chlorophyll molecules per complex Larger surface area than single chlorophyll Accessory pigments expand wavelengths absorbed Key Concept #3: The ~ sole source of energy that enables the low entropy state in all biology is light captured by photosystems to excite electrons so they can reduce other molecules o A single photon does not have enough energy to make NADPH o Photosystem II is a starting point for an electron transport chain – PS1 gives the ETC a “boost” of energy in order to reduce NADPH Key Concept #4: The light reactions of photosynthesis generate ATP using a proton gradient and ATP synthase just as in mitochondrial ATP synthesis o Ferrodoxin (Fd) can go on to reduce NADP+ (non-cyclic flow) or go “backwards” to make more ATP (cyclic flow) Non-cyclic flow is used to create NADPH and a proton gradient (and thus ATP), while cyclic flow is only used to make a larger proton gradient (and thus more ATP). Depending on the needs of the cell, it can adjust to either make more ATP or more NADPH o Summation of the “Light Reactions” so far: Non-cyclic Electron Flow 1 PS2: H 2+2 photons+PQ→ O +PQH 2 2 2 +¿gradient Cyt. b6f : ¿ PQH+2 Pc →ox+Pc +H ¿ PS1: 2Pc ¿2Fd +2oxhotons→2Pc +2Fd ox ¿ NDR: +¿→2Fd +NoxPH 2Fd +NADP+H ¿ ¿ +¿gradient 1 ¿ Total: +¿→ O +NA2PH+H 2 H2O+4 photons+NADPH+H ¿ o Summation of the “Light Reactions” so far: Cyclic Electron Flow: PS1: 2Pc ¿2Fd +2oxhotons→2Pc +2Fd ox ¿ FPO: +¿→2 Fd +Pox 2 2 Fd¿+PQ+H ¿ Cyt. B f : +¿gradient ¿ 6 PQH +2Pc →PQoxPc +bigger ox Total: +¿gradient ¿ 2 photons→bigger H
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'