Photosynthesis Experiment: Purple Bacteria - Lab Report Example

Photosynthesis Experiment: Introduction: Purple bacteria’s are among the first life forms on the earth. They derive their energy from photosynthesis.The solar energies that arrives form the sun are captured as small packets called photons are finely captured by the light capturing mechanism present in the photosynthetic membrane. Photosynthesis is the process in which the plants and some bacteria prepare their food. The primary processes of photosynthesis involve light absorption and the transfer of the energy synthesized in the chloroplast to the external system. (Kovacs et. al, 2006). Plant photosynthesis and the bacterial photosynthesis are similar in the synthesis of food. Bacterial photosynthesis uses the organic and sulfur compounds for the photosynthesis in the photo system I. The Photosynthetic reaction centre (RC) is found to be involved in the early steps of the photosynthesis at the photo system I. The involvement of the photon in the photo electric charge isolation in the bacteria is much regulated by the Photosynthetic reaction centre. The RC is capable of converting the photo energy into the electric energy. The RC neither binds to the substrate nor undergoes any chemical reactions. The photo energy for the RC is given by the extensive light harvesting complexes (LH). The light harvesting complexes are present in the photosynthetic apparatus. These light harvesting complexes funnels the harvested energy towards the RCs for energy conversion. The LHI and LHII are the light harvesting complexes used for the efficient funneling of the energy towards the RC. (Dreyfuss, 1994) LH I and LH II are formed by the same modular principle. They have an oligomer structure as the basic structural unit with a pair of hydrophobic apoproteins. The energy transfer reactions can be studied by using the pico second flash photolysis. It was also found that the apoproteins were having the polar N and C termini with a central hydrophobic region. The amino acid Histidine at the positions 30 and 31 are found be attached to the ligands of the Mg2+ of the bacteriochlorin rings in the LH I and LH II. ( Green, 2003). The light harvesting complexes are also called as the antenna complexes which involves the capturing of the photons. These antenna complexes are found to have involved in increasing the absorption of the light energy. The antenna complexes function as such that they supply each reaction centre with the enough number of photons with a wide variety of the light intensities. So when a mutation is done on the antenna complexes, the mutants will grow only at high light intensities. (Cogdell et. al, 1999). Materials and Methods: Three mutants were done on the genes of the light harvesting complexes LH I and LH II and on the Reaction center RC. The mutants were indicated with the minus sign and the wild type are indicated with the plus sign near their abbreviations such as LH- and LH+ . The mutant genes are found to have been cleaved out of their functions. Thus the non functioning genes are the mutant genes. The three bacteria with the following characteristics were inoculated into the 2 sets of the test tubes. They are ( 1) LH1+ LH2+ and RC + (2) LH1+ LH2- and RC+ (3) LH1- LH2+ and RC+ (4) LH1+ LH2+ and RC - . One set of the test tubes were kept under very high intensity sunlight and the other at low intensity sunlight and allowed to grow. Results: Test tube Growth at High Light intensity Growth at Low light intensity LH1+ LH2+ and RC+ Dark Brownish color Brownish color LH1+ LH2- and RC+ Dark Reddish color Pale reddish color LH1- LH2+ and RC+ Greenish color and little growth Very less growth LH1+ LH2+ and RC - No growth No growth (Garab, 1998) The results of the two sets of the test tubes are shown above. The LH1+ LH2+ and RC + test tube is dark brownish in the high light level and brownish at the low light level. The LH1+ LH2- and RC+ is reddish in the high light level and light reddish in the low light level. The LH1- LH2+ and RC + test tube has very low amount of growth even in the high and low level intensity light. The growth is minimum when compared to the wild type. The color of the bacterium also changes because of the mutant LH I complex. The last test tube with the genes LH1+ LH2+ and RC‑ shows no growth at all. There is no color in the test tubes at both the light intensities. Discussion: The LH1+ LH2+ and RC + test tube has no mutants and at high light level it showed the maximum growth because of the good supply of the photons by the light harvesting complexes I and II. The low light level also has good growth of the microorganisms, because the light harvesting antenna complexes absorbs light at a very broad spectrum than the reaction centers and so more amount of the solar energy called photons are used effectively. (Cogdell et. al, 1999). The LH1- LH2+ and RC + test tube has greenish color. This is due to the fact that the light harvesting complex I is mutated and thus very little amount of photosynthesis is carried out by the bacterium. The color of the bacterium also changes because of the mutant LH I complex. The last test tube has LH1+ LH2+ and RC- as the bacterial gene construct. Here the light harvesting complexes are wild and hence they are able to harvest the maximum amount of energy at both the high intensity and the low intensity light. But the reaction centre is mutant here. So there is no energy conversion in this test tube and finally no growth. From these experiments it is found that the RC complex is found to be very important for the photosynthesis of the bacteria. The further studies have proved that the chemicals that are required for the conversion of the light energy into the chemical energy is supplied by the RC. A mutation in these reaction complexes will result in the end of the photosynthesis of the bacteria. Whereas the mutation in the LH I and LH II will have a greater reduction of the photosynthesis but we can absorb some growth at the high intensity level of light. References: Cogdell et. al, RJ, (1999). How Photosynthetic Bacteria Harvest Solar Energy. Journal of Bacteriology. 181(13):3869-3879. Dreyfuss, BW and Thornber, JP. (1994). Assembly of the Light-Harvesting Complexes (LHCs) of Photosystem II (Monomeric LHC IIb Complexes Are Intermediates in the Formation of Oligomeric LHC IIb Complexes). Plant Physiology. 106(3): 829- 839. Garab G. (1998). Photosynthesis: mechanisms and effects. Springer publications. Green BR and Parson WW. (2003). Light-harvesting antennas in photosynthesis. Springer Publications. Kovács, L et. al. (2006). Lack of the Light-Harvesting Complex CP24 Affects the Structure and Function of the Grana Membranes of Higher Plant Chloroplasts, The Plant Cell. 18:3106-3120. Read More