5.4: Other Parts of the Cell
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- Valeria Hochman Adler
- Reedley College
Protein Synthesis: from the Nucleus to the Ribosomes
The central dogma of molecular biology states that DNA will be converted into RNA by a process called transcription and RNA will be converted to protein by a process called translation . Translation in non-reversible whereas transcription could be reverted: there are viruses, such as HIV, that can make DNA from RNA with the enzyme called reverse transcriptase . The nuclear envelope is built from a double-layered membrane. The inner and outer membranes of the nuclear envelope connect to form pores which are complicated structures controlling travel between the nucleus and the cytoplasm. Inside of the nuclear envelope there is the nucleoplasm.
Nuleoplasm contains chromatin (chromosomes). Chromosomes store genetic information in the form of DNA molecules. Each chromosome consists of a chain of nucleosomes, which are condensed long DNA molecules and their associated histone proteins. Chromatin is just another word for non-condensed chromosomes. Visible parts of chromatin (globules, filaments) correspond with non-functional DNA.
Ribosomes , which are particles that contain RNA and proteins, synthesize proteins. The rough endoplasmic reticulum (RER) has ribosomes along its surface, and the proteins they create are either secreted or incorporated into membranes in the cell. The Golgi apparatus (AG) is made of membranous sacs which are flattened and stacked, it modifies, packages, and sorts proteins and carbohydrates for the cell; this is not an essential component of cell.
Other Vesicles
Plant cells frequently have smaller vesicles: lysosomes which digest organic compounds and peroxisomes which, among other functions, help in photosynthesis (see above). In addition, many plant cells accumulate lipids as oil drops located directly in cytoplasm.
Cellular Skeleton
The cellular skeleton is a collection of protein filaments within the cytoplasm. Microtubules are key organelles in cell division, they form the basis for cilia and flagella and are guides for the construction of the cell wall. Cellulose fibers are parallel due to the microtubules. The movement in microtubules is based on tubulin-kinesin interactions. In contrast, the movement of microfilaments is based on actin-myosin interactions. Microfilaments guide the movement of organelles within the cell.