The NucleolusDrew 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.

LocationThe nucleolus is located in

the nucleusIt 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 oneIt dissipates during

mitosis when chromatin compacts into chromosomes

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

Nucleolus in a CellThe 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/FormationThe nucleolus is a bundle of chromatin, RNA, and

proteinsIt has two distinct parts: Fibrillar and GranularNucleoli form at Nucleolus Organizer Regions

(NORs), located at the ends of certain genesThe number of NORs determines how many nucleoli

form; however, one nucleolus can form from several NORsThe human nucleolus forms from 5 different pairs of

NORsIt is not held together by a membrane but stays

roughly spherical

Function of the Nucleolus: the Creation of RibosomesThe 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

FunctionProteins 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

Ribo

som

es

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 needsThis 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

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

Polypeptide(result)

Amino acid

http://www.absoluteastronomy.com/topics/Protein_biosynthesis

Bibliograpyhttp://

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)