Biology 1002B Chapter Notes - Chapter 2.3: Nuclear Localization Sequence, Nuclear Membrane, Nuclear Pore
2.3a Eukaryotic Cells have a True Nucleus and Cytoplasmic Organelles Enclosed within a
Plasma Membrane
• Cytosol: cytoplasmic solution surrounding organelles
• Plasma membrane: embedded proteins form channels for transport and others act
as receptors
• Cell wall: extracellular structure (since outside plasma membrane) of fungi, plants,
and many protists
• Animal cells do not have cell wall but have other extracellular structures
2.3b Eukaryotic Nucleus Contains Much More DNA Than Prokaryotic Nucleoid
• Nuclear envelope
o Nucleus separated from cytoplasm by double membraned nuclear envelope
o Lamins: intermediate filaments that line inner surface of nuclear envelope in
animal cells
o Unrelated proteins line inner surface of nuclear envelope in protists, fungi,
and plants
o Nuclear pore complex: octagonally symmetrical structures formed of
proteins called nucleoporins, which control the transport of molecules
between nucleus and cytoplasm
o Nuclear pore: opening in nuclear envelope through which large molecules
like RNA move
• Some proteins must be imported into nucleus to carry out functions
o Nuclear localization signal: short AA sequence that distinguishes between
which proteins must be imported and which stay in cytosol
o Specific protein in cytosol recognizes and binds to signal, then moves protein
to nuclear pore complex
• Within the nucleus
o Nucleoplasm: liquid substance within nucleus
o Most space is filled with chromatin (combination of DNA and proteins)
o Genetic info distributed among many linear DNA molecules
o Eukaryotic chromosome: each individual DNA molecule with its associated
proteins
o Chromatin: any collection of eukaryotic DNA molecules with their associated
proteins
o Chromosome: one complete DNA molecule with its associated proteins
o Eukaryotic nuclei contain much more DNA than prokaryotic nucleoids
• Nucleolus
o Nuclear site of rRNA transcription, processing, and ribosome assembly in
eukaryotes
o Form around genes which code for rRNA molecules
o Here, rRNA molecules combine with proteins to form ribosomal subunits
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