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Drew Blazewicz, Maia Dinsmore, and Megan Durning Vocabulary Mitosis – the division of a single nucleus into two daughter nuclei; part of cell reproduction Chromatin – a combination of DNA and proteins that constitutes eukaryotic chromosomes Chromosomes - a threadlike, gene carrying structure found in the nucleus of a eukaryotic cell RNA – ribonucleic acid, a type of nucleic acid consisting of nucleotide monomers, formed from the transcription of DNA Nucleotides – building blocks of nucleic acids Monomer – a chemical subunit that serves as a building block of a polymer Polymer – a large molecule consisting of many identical or similar molecular units (monomers), covalently joined together in a chain. An example of this is DNA Filaments – a very fine threadlike structure (dictionary.com) All definitions taken from Biology: Concepts and Connections, unless otherwise stated. Location The nucleolus is located in the nucleus It can take up as much space as 25% of the nucleus Animals can have more than one nucleolus, depending on the species Humans only have one It dissipates during mitosis when chromatin compacts http://micro.magnet.fsu.edu/cells/nucleus/nucleolus.html into chromosomes Nucleolus in a Cell The nucleus (red) is filled with nucleoplasm (green), in the center of which rests the nucleolus (orange) Surrounding the nucleus, filling the rest of the cell, is cytoplasm (blue). http://www.biologyreference.com/Mo-Nu/Nucleolus.html Composition/Formation The nucleolus is a bundle of chromatin, RNA, and proteins It has two distinct parts: Fibrillar and Granular Nucleoli form at Nucleolus Organizer Regions (NORs), located at the ends of certain genes The number of NORs determines how many nucleoli form; however, one nucleolus can form from several NORs The human nucleolus forms from 5 different pairs of NORs It is not held together by a membrane but stays roughly spherical Function of the Nucleolus: the Creation of Ribosomes The first step in the process of creating ribosomes, which are organelles involved in protein synthesis, is the transcription of DNA into ribosomal RNA This occurs at the nuclear organizer region of the nucleolus The transcribed rRNA surrounds the NOR in a dense ring of filaments called pars fibrosa RNA transcription http://www.cytochemistry.net/cell -biology/nucleus3.htm Function Proteins are then combined with the rRNA, which form ribonucleoproteins These form the subunits of ribosomes Ribonucleoproteins surround the pars fibrosa in a layer called the pars granulosa http://www.cytochemistry.net/cell-biology/nucleus3.htm http://www.biologie.uni-hamburg.de/b-online/library/onlinebio/BioBookCELL2.html Ribosomes are then formed from the two subunits - a large subunit and a small subunit, created in the nucleolus They are involved in protein synthesis, the translation of RNA into proteins The number of nulceoli an animal has is determined by the amount of proteins it needs This is because an animal needs more ribosomes in order to create a larger number of proteins, and it therefore would need more nucleoli to produce these ribosomes. A healthy cell can create up to 10,000 ribosomes per minute Protein Synthesis (to be explained in more detail later in class) In the first step of protein synthesis, mRNA is transcribed (copied) from the DNA in the nucleus Messenger RNA (mRNA), which forms in the nucleus, binds to the ribosomes Transfer RNA (tRNA), carries amino acids to the ribosomes The order of nucleotides in the mRNA determines the order of amino acids in the polypeptide that is created, this process is called translation Therefore, the nucleolus has an indirect effect on protein synthesis Amino acid Polypeptide (result) http://www.absoluteastronomy.com/topics/Protein_biosynthesis Bibliograpy http://micro.magnet.fsu.edu/cel ls/nucleus/nucleolus.html (images and information) http://www.biologyreference.co m/Mo-Nu/Nucleolus.html (images and information) http://www.cytochemistry.net/c ell-biology/nucleus3.htm (images and information) http://www.absoluteastronomy. com/topics/Protein_biosynthesi s (image) Campbell, Neil A. Biology. 2nd ed. Redwood City, CA: Benjamin/Cummings, 1987. Print. (information) http://www.biologie.uni- hamburg.de/bonline/library/onlinebio/BioBoo kCELL2.html (image) http://books.google.com/books? id=LorrYj5pkKYC&pg=PA839&lp g=PA839&dq=pars+fibrosa&sour ce=bl&ots=Kza6AjnZq2&sig=t2q EX8lndfVrBVO4sj0fDkAi8tY&hl =en&ei=QNLqTKmAKous8Ab1w rnUDA&sa=X&oi=book_result& ct=result&resnum=7&ved=0CD8 Q6AEwBg#v=onepage&q=pars% 20fibrosa&f=false (information) Helena, Curtis. Biology. 4th ed. New York, NY: Worth, 1983. Print. (information)