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Chapter 9 Cellular Respiration and Fermentation, Chapter 10…

- - - - Obligate Anaerobes: carry out only fermentation or anaerobic respiration
  - - - Brown Fat Tissue: found in hibernating mammals are packed full of mitochondria and assist with maintaining body temperature during a state of inactivity
- - - - Pigments: substances that absorb visible light
        Photosynthetic Pigments: Light Receptors
        
        Spectrophotometer: instrument that measures the ability of a pigment to absorb various wavelengths of light
        
        HOW: the machine directs beams of light of different wavelengths through a solution of the pigment and measures the fraction of the light transmitted at each wavelength
        
        Absorption Spectrum: a graph plotting a pigment's light absorption versus wavelength
        
        action spectrum: profiles the relative effectiveness of different wavelengths of radiation in driving the process
        
        Absorption spectra of chloroplast pigments:
        - (chlorophyll a) the key light-capturing pigment that participates directly in the light reactions, violet-blue & red light are most effective for photosynthesis
        
        (chlorophyll b) - the accessory pigment
        
        (Carotenoids) a separate group of accessory pigments, hydrocarbons that are various shades of yellow and orange because they absorb violet and blue-green light
        
        important function is photoprotection, they absorb and dissipate excessive light energy that would otherwise damage chlorophyll or interact with Oxygen, forming reactive oxidative molecules that are dangerous to the cell.
        
        phytochemicals for antioxidant properties
- - - - Phase 1: Carbon Fixation via C3 plants
        
        Co2 is attached to 5-C sugar named RuBP (ribulose bisphosphate)
        
        the enzyme that catalyzes this is rubisco (RuBP caboxylase-oxygenase)
        
        The product of the rxn is 6-C intermediate that is unstable and splits in half forming 2 molecules of 3-phosphoglycerate (for each CO2 fixed)
        
        Phase 2: Reduction
        
        Each molecule of 3-phosphoglycerate receives an additional group from ATP, creating the 1, 3-bisphosphoglycerate
        
        Pair of electrons donated from NADPH reduces 1, 3-bisphosphoglycerate, which loses a phosphate group in the process, becoming glyceraldehyde 3-phosphate (G3P)
        
        Electrons from NADPH reduce a carboxyl group on 1, 3-bisphosphoglycerate to the aldehyde group of G3P which stores more potential energy, for every 3 CO2, there are 6 G3P made, but only 1 is netted as gain, because the other 5 are required to complete the cycle.
        
        One molecule exits the cycle to be used by the plant cell, the other 5 recycle to regenerate the 3 molecules of RuBP
        
        Phase 3: Regeneration
        
        This is the phase were we regenerate the CO2 receptor (RuBP)
        
        5 GEP molecules rearrange into 3 molecules of RuBP
        
        RuBP is now prepared to receive CO2 again and cycle continues
        
        Total Reactants:
        
        9 molecules of ATP
        
        6 molecules of NADPH
        Total Product:
        
        1G3P
        
        2 G3P make 1 Glucose
        
        Alternative mechanisms of Carbon fixation evolved in hot, arid climates
        
        Evolution has forced organism to adapt particularly to the problem of dehydration.
        
        an example is the balance btw photosynthesis and the prevention of excessive water loss from the plant.
        
        Stomata: the pores on the surface of the leaf that allows the CO2 to enter and O2 to exit via photosynthesis and evaporative loss of water from leaves (transpiration)
        
        Photorespiration: occurs in the light (Photo) and consumes O2 while producing CO2 (respiration)
        
        produces no sugar
        
        uses ATP rather that generating it
        
        decreases photosynthetic output by siphoning organic material from the Calvin cycle and releasing CO2 that would otherwise be fixed.
        - a metabollic relic from a time when the atmosphere had less O2 and more CO2 than it does today.
        
        In fact if photorespiration could be reduced in certain plant species without affecting photosynthetic productivity, crop yields and food supplies might increase
        
        C4 Plants: Alternative mode: when hot and dry C4 partially close stomata conserving water but reducing CO2 concentration in leaves, sugar is still made
        
        Photosynthesis begins in mesophyll cells and is completed in bundle-sheath cells.
  - - - Reaction-Center Complex:
        an organized association of proteins holding a special pair of chlorophyll a molecules and a primary electron acceptor
        
        Light-Harvesting complex:
        
        consists of various pigment molecules bound to proteins
        
        pigments may include chlorophyll a, chlorophyll b, and multiple carotenoids
        
        the act as an antenna for the reaction-center complex
        
        Primary Electron Acceptor : a molecule capable of accepting electrons and becoming reduced
  - - - Steps of Linear Electron Flow:
        
        A photon of light strikes one of the pigment molecules in a light harvesting complex of PS II, boosting one of its electrons to a higher energy (it bumps another molecule as it falls back like a chain reaction) and continues until it reaches P680, where it excites an electron in chlorophyll to a higher state
        
        Electron is transferred from excited P680 primary electron acceptor and results in P680+
        
        An Enzyme catalyzes the splitting of a water molecule into two electrons, two Hydrogen ions (H+), and an oxygen atom. The electrons are supplied to P680+ replacing one transferred to the primary electron acceptor. H+ are released into thylakoid space. Oxygen immediately combines with another Oxygen generated by splitting of another water molecule forming O2
        
        Each Photoexcited electron passes from Primary Electron Acceptor of PS II to PS I via an electron transport chain, made up of Pq (plastocyanin), a cytochrome complex, and a protein called Pc (plastocyanin). Each component carries out redox reactions as electrons flow, releasing energy that is used to pump protons (H+) into the thylakoid space, contributing to the proton gradient across the thylakoid membrane.
        
        Potential energy stored in proton gradient is used to make ATP in a process called Chemiosmosis
        
        light energy has been transferred to PS I reaction-center complex, exciting P700 pair of chlorophyll a primary electron acceptor, which is at the bottom of ETC
        
        Photoexcited electrons are passed via redox reactions from PS I down a second ETC through protein ferrodoxin (Fd). This does not create a protein gradient
        
        The enzyme NADP+ reductase catalyzes the transfer of electrons from Fd to NADP+. 2 electrons required for its reduction to NADPH, which will be at a higher energy level and more readily available for reactions within the Calvin Cycle, this also removes a H+ from stroma
        
        Comparison of Chemiosmosis in Chloroplasts and Mitochondria
        
        Chloroplasts don't need molecules from food to make ATP, their photosystems capture light energy and use it to drive the electrons from water to the top of the transport chain
        
        Mitochondria use it to transfer chemical energy from food molecules to ATP
        
        Chloroplast use it to transform light energy into chemical energy in ATP
      - Proton (H+) gradient or pH gradient
- - - - Step 3: During Oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis
        
        Oxidative Phosphorylation:
        the mode of ATP synthesis, powered by the redox reactions from the electron transport chain and chemiosmosis
        
        accounts for 90% of the ATP generated by respiration
        
        Electron Transport Chain: Does not directly make ATP, but instead reduces the FADH & NADH and passes e- through creating the H+ gradient to power the H+ ion pump
        
        Chemiosmosis:
        - the process by which energy stored in the form of Hydrogen ion gradient across a membrane and used to drive cellular work, (such as synthesis of ATP).
        
        Its the connector btw ETC and STP Synthesis
        -ATP Synthase makes ATP from ADP and inorganic phosphates like a ion pump in either direction
        
        located in the inner membrane of the mitochondria in eukaryotic cells & in prokaryotes, it takes place in the plasma membrane
        
        Products:
        
        ATP
        
        FAD
        
        NAD+
        
        H20 (2H+ & e- are passed to O2)
        
        Cytochromes:
        
        remaining electron carriering proteins btw ubiquinone an oxygen
        
        Several within the ETC all "cyt"
        
        Proton-motive force: the H+ gradient created by ETC, emphasizes the capacity of the gradient to perform work
      - Substrate-level phosphorylation: when an enzyme transfers a phosphate group from a substrate molecule to ADP, rather than adding an inorganic phosphate to ADP
        
        Products:
        
        2 ATP
        
        2 CO2
        
        3 NADH, H+
        
        FADH2
      - Anabolic Pathways (Biosynthesis):
        
        Calories used to provide the carbon skeletons that cells require to make their own molecules
        
        Glycolysis and Citric Acid Cycle function as metabolic interchanges that enable cells to convert some kinds of molecules to others as needed
      - Feedback Inhibition - cells do not waste energy making more o a particular substance, the anabolic pathway that synthesizes that amino acid from an intermediate of the citric acid cycle is switched off, & end product inhibits the enzyme that catalyzes the early step of pathway