Photosynthesis is an essential process for life on earth because it allows the assimilation of carbon in the form of carbohydrates. Photosynthesis takes place in a special organelle, the chloroplast. Around 2000 proteins are required to build a functional chloroplast. The genes for most of these proteins are on chromosomes in the cell nucleus. Therefore, the proteins are made in the cytosol and imported into the chloroplast. During their import, proteins must traverse the two envelope membranes of the chloroplast. Import involves a molecular transport machine in the envelopes consisting of Translocons at the outer (Toc) and inner envelope membrane (Tic). Toc159 and Toc33 are important receptor components at the surface of the organelle. They first recognize the chloroplast proteins and then facilitate their import. Together, they are absolutely needed to make the chloroplast. Both Toc159 and Toc33 are known to be switched on and off by GTP. Our goal is to understand how the GTP molecular switch works to accomplish protein import and allow the development of the photosynthetic chloroplast.