Non-Membrane-Bound Cell Organelles

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Chapter 3

• Non-Membrane-Bound Cell Organelles
• James F. Thompson, Ph.D.

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The Organelles of Typical Cells

• Cytoplasmic organelles you should know
• Mitochondria
• Ribosomes
• Rough endoplasmic reticulum (Rough ER)
• Smooth endoplasmic reticulum (Smooth ER)
• Golgi apparatus
• Lysosomes Peroxisomes
• Cytoskeleton
• Nucleus
• Nucleoli
• Inclusion bodies substances
• not enclosed in membrane

• Centrioles
• Cilia
• Flagella

not membrane-bound
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Ribosomes
Ribosomes self assemble from rRNA molecules and
proteins. They form two subunits which come
together to form the functional whole, the
ribosome, which is where translation, the
synthesis of protein molecules occur.
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Ribosomes
Ribosomes are located in the general cytoplasm or
may shift to become attached to the cytoplasmic
side of the rough endoplasmic reticulum (RER)
another set of ribosomes are located inside
mitochondria.
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Ribosomes
Ribosome surface features ensure that the mRNA
and tRNAs align correctly for the translation of
proteins.
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The Cytoskeleton
The three main cytoskeletal elements are the
fibrous proteins microtubules, intermediate
filaments and microfilaments.
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Microtubules

• Large diameter, hollow tubes made of coiled
  tubulin subunits.
• They assemble or disassemble as needed, using ATP
  energy.
• They anchor and move organelles in the cytoplasm.
• They form the spindle fibers seen in nuclear
  divisions (mitosis and meiosis) which move the
  chromosomes to the cell poles.

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Intermediate Filaments

• Four families of intermediate filaments are
  known.
• Some give shape to cells like a scaffolding.
• Some bind to cytoskeletal anchors and to cell
  junctions such as desmosomes.
• They are less involved in cell movements.

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Microfilaments

• The smallest filament are composed of actin
• They are involved in cell motility and cell
  shape
• They are responsible for muscle contraction when
  actin interacts with myosin

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Microfilament- and Microtubule- Dependent Motility
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The Nucleolus / Nucleoli
hepatocytes
They are dark staining, oval/spherical bodies
within the nucleus of cells which are
synthesizing large quantities of proteins
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The Nucleolus / Nucleoli

• They are composed of clusters of DNA, RNA, and
  proteins
• They are the sites of ribosomal RNA synthesis and
  ribosomal subunit assembly
• They disappear during nuclear divisions and
  reappear later

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Centrosome Centromeres

• Centrosome
• Microtubule organizing center
• Contains centrioles
• Centrioles
• Involved in mitosis and orient the spindle fibers
  to the poles of the dividing cell
• Give rise to cilia and flagella

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Centrosome Centromeres
Note Cilia and flagella are membrane bound
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Inclusion Bodies
Reticulocytes are immature red blood cells which
do not have a cell nucleus. They are called
reticulocytes because of a reticular (mesh-like)
network of ribosomal RNA that becomes visible
with certain special stains.
Sporadic inclusion body myositis (IBM) is the
most common muscle disease in old people.
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End Chapter 3

• Non-Membrane-Bound Cell Organelles