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
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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



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(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
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

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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)