Cell Biology 1.) What is Rubisco? What is its role in the process of photosynthe

Question

Cell Biology

1.) What is Rubisco? What is its role in the process of photosynthesis?

2.) Describe (or draw and carefully label) the light reactions of photosynthesis.   Be sure to describe how the two photosystems in plants differ from one another, but yet cooperate in producing the light reaction products. Clearly indicate how and where the final products of the light reactions of photosynthesis (i.e., O2, NADPH and ATP) are formed.   

3.) Dysfunction of the multidrug resistance transporter 1 (MDR1) has been implicated in both drug resistance and drug sensitivity, depending on the clinical situation. Explain what this transport protein is, how it normally functions, and how it can hamper the treatment of cancer or result in toxicity if not functioning normally.

Explanation / Answer

1. Ribulose-1,5-bisphosphate carboxylase or Rubisco is a major enzyme which is involved in the first important step of carbon fixation. The reaction involving Rubisco condenses a CO2 molecule with ribulose 1,5-bisphosphate (a five carbo molecule) to produce a transient six-carbon intermediate that rapidly hydrolyzes to two molecules of 3-phosphoglycerate.

2. The light reaction takes place in the tylakoid membranes. The light reaction utlizes sunlight to synthesize NADPH and ATP. The overall reaction is 2H2O + 2NADP+ + 3ADP + 3Pi O2 + 2NADPH + 3ATP. Green plants and algae typically use two types of photosystems called photosystem I (PSI) and photosystem II (PSII). The chlorophyll in the reaction centre of PSI has an absorption maximum at 700nm and is called P700, whereas the absorption maximum for PSII is 680nm and is hence P680. The two photosystems are linked together by electron carriers which are arranged according to their redox potentials. Hence the whole system forms kind of a Z scheme.

3. The multidrug transporter or P-glycoprotein is a membrane transporter found on the cell membrane where it is involved in the ejection of detrimental chemicals or xenobiotic agents out of the cell. Thus, if the MDR1 fails to eject these xenobiotic agents, they can be dangerous for the cell leading to their death. However, these transporters are a big menace too. In tumor cells they are involved in effluxing the chemotherapeutic agents that are meant to target and kill the tumor cells. Hence they prevent the treatment of cancers.

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