Post on 21-May-2015
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The Cytoskeleton
• A networked mesh of protein rods that support the cell, acting as scaffolding
• Also contain contractile units that allow for the movement of cells and for intracellular movement (organelle movement, vesicular transport)
• Three Types:
– Microtubules
– Microfilaments
– Intermediate filaments 1
Microfilaments
• Thin (but dense),
cross-linked strands
of actin (contractile
proteins)
• Involved in cell
motility and changes
in shape
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Intermediate Filaments
• Tough, stable,
permanent, rope-like
protein fibers
• Have high tensile
strength
• Helps cells resist
mechanical stress
and are found in
desmosomes for cell-
cell contact 3
Microtubules
• Long, hollow tubes
composed of tubulin.
Large in diameter
• Radiate from the
centrosome
• Determine cell shape
and organelle
distribution
• Important in
intracellular transport 4
Centrosome & Centrioles
• “microtubule organizing
center”
• Composed of two
centrioles (90o to each
other) and a granular
matrix
• Matrix generates
microtubules
• Centrioles generate
spindle fibers during cell
division 5
Cellular Extensions: Cilia
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Cellular Extensions: Flagella
• Sperm cells are the
only cells in the
human body with
flagella
• Similar to cilia but are
longer and allow cells
to propel themselves
• Use a whip-like
motion for locomotion
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Cellular Extensions: Microvilli
• Finger-like plasma membrane projections
• Increases plasma membrane surface area
• Typically found in absorptive cells
• Example: Lining of the small intestine 8
The Nucleus
• The “control center” of
the cell containing
genetic information
• The largest organelle of
the cell and is filled with
nucleoplasm
• Composed of: Nuclear
envelope, Nucleolus,
and Chromatin 9
The Nuclear Envelope
• Double membrane barrier
separated by a fluid-filled space
• Outer membrane is continuous
with RER & is studded with
ribosomes
• Inner membrane is lined with
nuclear lamina
• Two membranes come together
and form nuclear pores (entry and
exit point of particles) 10
Nucleoli
• Small, dense body
composed of RNA and
protein, where
ribosomes are
synthesized
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Chromatin
• Loosely coiled DNA fibers
and histone proteins,
condense to form
chromosomes.
• DNA + histone =
nucleosome
• Condense into
chromosomes during cell
division
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The Cell Cycle
• Cell cycles form a multi-
celled organism from one
original cell
• A series of changes cells go
through from the time they
are formed until they divide
• Promote growth and tissue
repair in organisms
• Involves phases and
checkpoints for quality
control
*Movie time! 13
Interphase • Cell growth and DNA
replication, “preparation
period”
• G1 Phase: Growth Phase
1, structures are
duplicated
• S Phase: Synthesis
Phase, DNA is replicated
• G2 Phase: Growth Phase
2, more structural
duplication, final
preparations
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DNA Replication
• Occurs before cell division
• DNA is uncoiled & H-bonds broken by a helicase
• DNA polymerase introduces complementary bases
• Replicated DNA is semi-conservative
• DNA condenses after replication 15
Mitosis
• Division of the nucleus:
– Prophase
– Metaphase
– Anaphase
– Telophase
• Cytokinesis: Division of the cytoplasm
• Exceptions: RBCs, nervous, skeletal &
cardiac tissue
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Mitosis
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Mitosis
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Protein Synthesis
• DNA provides the
information for
protein synthesis
• Two events:
– Transcription
– Translation
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Transcription
• Synthesis of
complementary
mRNA (messenger
RNA)
• Transcribes the
code for making
proteins and
transports it outside
the nucleus 20
Translation
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Translation
• Every mRNA codon
corresponds to an
amino acid
• Examples:
– CAC = Histidine
– CAA = Glutamine
– AAA = Lysine
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