Breifly explain how a chloroplast structural protein is built, modified, and transported to the chloroplast. Make sure to mention the following organelles or cell parts in your answer: chloroplast, rough endoplasmic reticulum, Golgi, nucleus, ribosome,
Cell Structure
The knowledge and concept about the structure of the cells have changed constantly over the past years. Primarily the scientist defines the cells as a simple membranous sac with fluids and some particles. Researches have now revealed that the cell is the more complex and basic unit of life. There are different types of cells and they also differ in shape and structure. The basic three parts of a cell are cell membrane, cytoplasm, and organelle.
Plant Cell
The smallest functional unit of a living organism is known as the cell. It is composed of cytoplasm enclosed by an outer layer known as the cell membrane. A cell is classified as a prokaryotic cell and a eukaryotic cell. A prokaryotic cell does not contain a nucleus, and the genetic material is freely suspended in the cell cytoplasm; for example, bacteria are composed of a prokaryotic cell. Whereas a eukaryotic cell contains a nucleus and membrane-bound cell organelles with a specific function, plants and animal cells are examples of eukaryotic cells.
Plant Cell Types
Plants are made up of a variety of cell types that include both living and dead cells. These cells provide them mechanical and structural support along with the growth of plants. Plant tissue is a group or collection of cells, which are similar in structure and work together to accomplish a specific function. Plant cells are most similar to animal cells, both being eukaryotic cells.
Breifly explain how a chloroplast structural protein is built, modified, and transported to the chloroplast. Make sure to mention the following organelles or cell parts in your answer: chloroplast, rough endoplasmic reticulum, Golgi, nucleus, ribosome,
Most nuclear-encoded chloroplast proteins are synthesized on cytosolic ribosomes as larger precursors. They carry an N terminal extension called the transit peptide, which is necessary and sufficient for postranslational targeting and import into chloroplasts. Transit peptide-dependent protein import is known as the general pathway. It is catalyze by the translocon at the outer-envelope-membrane of chloroplasts (TOC) and translocon at the inner-envelope-membrane of chloroplasts (TIC) complexes, which couple ATP hydrolysis in the stroma with protein transport across the envelope membranes.
The TIC complex constitutes the protein-conducting channel in the IEM and facilitates coupling of ATP hydrolysis by the stromal motor with transport of proteins across the membrane. Transit peptides are cleaved by a soluble metallopeptidase called SPP in the stroma , and the resultant proteins either stay and fold within this aqueous compartment, or are further sorted to the IEM or thylakoid . Most proteins found in the OEM as well as some proteins localized in the IEM and the stroma do not carry transit peptides, and their import appears to be independent of TOC/TIC .
Preproteins may be recognized at the outer envelope and translocated in a single step across the outer and inner membrane through contact zones where the two membranes are maintained in close apposition. The targeting signal for envelope translocation is in the N-terminal bipartite “transit sequence.” The N- and C-terminal portions of this sequence contain chloroplastic and intraorganellar targeting information, respectively. Translocation to the stroma occurs in at least two steps and requires the hydrolysis of both ATP and GTP. Subsequently, the transit sequence is removed in the stromal compartment.
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