{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Experiment 4 - BC368 Biochemistry of the Cell II Experiment...

Info icon This preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
BC368 – Biochemistry of the Cell II Experiment 4 Inhibition of Photosynthetic Electron Transport by Substituted Quinones Introduction Light energy is transformed into chemical energy by the process of photosynthesis. Photosynthesis is initiated by absorption of a photon by one of many possible organic pigments present in the cell. These pigments include the chlorophylls and the carotenoids, the combined absorbances of which cover a large region of the spectrum between 400-700 nm. Light absorbance triggers a series of oxidation-reduction events, resulting ultimately in the oxidation of water to molecular oxygen and hydrogen ions and the concomitant reduction of carbon dioxide. The overall reaction as it occurs in green plants can be represented as follows: CO 2 (g) + H 2 O(l) [CH 2 O](aq) + O 2 (g) Photosynthesis occurs in both green plants and some bacteria. While anaerobic bacteria use substrates other than water as the electron donor, the overall molecular logic is very similar. The mechanism of photosynthesis involves two stages: the “light” reactions, which require light to occur, and the “dark” reactions, which do not require light (but do occur in the daytime!). The light reactions are the focus of this experiment, which will use spinach chloroplasts as the source of the photosynthetic apparatus. Structure of the Chloroplast Spinach chloroplasts are small ellipsoid structures of about 4-10 μ m in diameter and 1 μ m in thickness. A double membrane system encloses the fluid interior, called the stroma, which contains the enzymes of the dark reactions. Isolated chloroplasts contain the internal membranes, called the thylakoid membranes, within which is the machinery of the light reactions. Conveniently, thylakoid membranes can be isolated from green plant material through mechanical fractionation and differential centrifugation. Measurement of Photosynthetic Activity In this exercise, you will be measuring light-induced electron transfer activity in isolated plant chloroplasts by monitoring the reduction of the same artificial electron acceptor that you used in Experiment 3. When chloroplast membranes are isolated, the electron transport chain is left without a terminal electron acceptor. 2,6- dichlorophenolindolphenol (DCPIP) is not only of suitable redox potential to serve this purpose, but its reduction can also be conveniently monitored colorimetrically: E-FADH 2 + DCPIP oxidized E-FAD + DCPIP reduced (blue) (colorless) Cl O Cl N O - Na + oxidized form of DCPIP h υ Δ G = 480 kJ/mol
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
BC 368- Experiment 4- Spring 2010 2 Inhibition of Photosynthesis Electron transport can be inhibited in the presence of certain compounds that act as herbicides. The compounds that you will study in this exercise are structural analogues of the mobile electron carrier Q B , a nonpolar plastoquinone. Q B shuttles reducing equivalents from the membrane-bound protein complex Photosystem II to the cytochrome bf complex. Oxidized Q B binds via specific interactions to one of the protein components of Photosystem II and acts as a two-electron acceptor. The reduced form
Image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern