The centriole is the dense centre of the centrosome.Ī vast system of interconnected, membranous, in-folded and convoluted sacks that are located in the cell’s cytoplasm (the ER is continuous with the outer nuclear membrane). During cell division (mitosis), the centrosome divides and the two parts move to opposite sides of the dividing cell. The centrosomes are where microtubules are made. It has a dense center and radiating tubules. These are then exported out of nucleus through nuclear pores.Ī small body located near the nucleus, also called the ‘microtubule organizing centre’. These two elements are integrated inside nucleolus to create ribosomal subunits. Ribosomal proteins are made in cytoplasm and transported back into the nucleus. The nucleolus is present within the nucleus. Some signals allow motion in but not out, other signals control reverse transport.
They can open up to as much as 26 nm in response to certain signals. Pore diameter is about 10 nanometers (10 x 10 -9 m), smaller than the diameter of a complete ribosome. The pores have octagonal ‘doors’ made of protein which open and close on either side depending on specific signals. These pores allow different materials to move in and out of nucleus. The nuclear membrane is a double layered structure surrounding the nucleus containing many nuclear pores. Chromatin can condense into chromosomes during cell division. It contains chromatin i.e., DNA-protein complexes. It is the locus of DNA/RNA synthesis and protein assembly. The nucleus is surrounded by the nuclear membrane. It controls many of the functions of the cell (by controlling protein synthesis) and contains DNA (in chromosomes). It is a spherical body containing many organelles, including the nucleolus.
Less in many specialized eukaryotic cells but still are the dominant activity of almost all the cells. In bacteria they occupy 25% of cell volume and use 90% of cell energy. In prokaryotes the ribosomes are made of 30S and 50S subunits, assemble into 70S ribosome whereas in eukaryotes the ribosomes are made of 40S and 60S subunits, assemble into 80S ribosome.
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