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The Nucleolus

The Nucleolus. 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

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The Nucleolus

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  1. The Nucleolus Drew Blazewicz, Maia Dinsmore, and Megan Durning

  2. 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.

  3. 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 into chromosomes http://micro.magnet.fsu.edu/cells/nucleus/nucleolus.html

  4. 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

  5. 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

  6. 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

  7. Function • Proteins are then combined with the rRNA, which form ribonucleoproteins • These form the subunits of ribosomes • Ribonucleoproteins surround the pars fibrosain a layer called the pars granulosa http://www.cytochemistry.net/cell-biology/nucleus3.htm

  8. Ribosomes • 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 http://www.biologie.uni-hamburg.de/b-online/library/onlinebio/BioBookCELL2.html

  9. 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

  10. Bibliograpy • http://micro.magnet.fsu.edu/cells/nucleus/nucleolus.html (images and information) • http://www.biologyreference.com/Mo-Nu/Nucleolus.html (images and information) • http://www.cytochemistry.net/cell-biology/nucleus3.htm (images and information) • http://www.absoluteastronomy.com/topics/Protein_biosynthesis (image) • Campbell, Neil A. Biology. 2nd ed. Redwood City, CA: Benjamin/Cummings, 1987. Print. (information) • http://www.biologie.uni-hamburg.de/b-online/library/onlinebio/BioBookCELL2.html (image) • http://books.google.com/books?id=LorrYj5pkKYC&pg=PA839&lpg=PA839&dq=pars+fibrosa&source=bl&ots=Kza6AjnZq2&sig=t2qEX8lndfVrBVO4sj0fDkAi8tY&hl=en&ei=QNLqTKmAKous8Ab1wrnUDA&sa=X&oi=book_result&ct=result&resnum=7&ved=0CD8Q6AEwBg#v=onepage&q=pars%20fibrosa&f=false (information) • Helena, Curtis. Biology. 4th ed. New York, NY: Worth, 1983. Print. (information)

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