Download 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
 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
(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)