Question

SHORT ANSWER

23. Describe the path of electrons in the noncyclic electron transport pathway during photosynthesis. Explain the difference between the pathway of electrons in cyclic and noncyclic electron flow and in the final products that result from each pathway.

24. Cytochalasin is a drug that binds to the plus ends of actin filaments, thereby blocking elongation. Because of the dynamic nature of actin filaments this usually results in the depolymerization of actin filaments. a. If you were studying the cell cortex and desmosomes and treated cells with cytochalasin, which of the two structures would you expect to breakdown? b. After treatment of the cells with the drug, you observe a major change in one of the structures, but also observe a minor change in the other structure. Why do you think the drug influenced one structure to a minor extent?

25. Several proteins and enzymes are involved in assuring that proteins fold into the correct shape after synthesis. One example is molecular chaperone proteins. Another is protein disulfide isomerase (abbreviated PDI), which catalyzes the breakage and re-formation disulfide bonds to allow the protein to attain the most stable conformation. Disulfide bonds are important in stabilizing the folded structure of secreted proteins and membrane surface proteins. a. Based on this information, in which fraction do you predict PDI to be found after subcellular fractionation: cytosol, mitochondria, or endoplasmic reticulum? b. Explain your prediction giving reference to the topography of the cell and subcellular compartments.

26. Describe the mechanism by which lysosomal proteins are targeted to the lysosome.

Answer 1

23. In the non cyclic pathway, electrons produced from splitting of water move from photosystem 680 to the primary electron acceptor, from where these are captured by plastoquinone to cytochrome acceptor to plastocyanin and then PS 700. From this photosystem, through ferrodoxin, electrons are taken up by NADH reductase and produce NADH. In the cyclic pathway, only photosystem 700 operates. In cyclic flow, only ATP is formed while in non cyclic flow, both ATP and NADH are formed.

24. After treatment of the cells with cytochalasin, cell cortex is damaged to the major extent. Cytochalasin affects the desmosomes to minor extent because desmosomes involve internediate filamenst which are nit affected by cytochalasin.

25. PDI would be found in mitochondria. Nucleus is present in the middlw of the cell connected to endoplasmic reticulum while mitochondria is scattered around. After the settlement of nucleus, mitochondria is obtained in subcellular fractionation process.

26. Lysosomal proteins are targeted to lysosomes due to the presence of mannose -6- phosphate tag on them placed in the golgi bodies to target them to lysosomes with the help of vesicles.