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CELL STRUCTURES Sources : Campbell, N. 1993 Biology Third Edition. Benjamin Cummings Publishing. United States. Wallace, S. 1993 Biology The Cytoskeleton The cytoskeleton (high voltage transmission electron microscope)

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cell structures



Campbell, N. 1993 Biology Third Edition. Benjamin Cummings Publishing. United States.

Wallace, S. 1993 Biology

the cytoskeleton
The Cytoskeleton
  • The cytoskeleton (high voltage transmission electron microscope)
    • Microfilaments (very fine; 6 nm in diameter). mostly made up of protein actin. Have a variety of roles depending on the type of proteins they are associated with:
      • one is to provide support to the plasma membrane
      • form supportive network of microvilli (intestinal wall)
      • also involved in the pinching of the cell membrane during cell division
Intermediate filaments (diameter 7 nm): Role is poorly understood.
    • Found in epithelial cells, nerve cells, muscle cell fibers and blood cells.
    • Made up of the protein keratin.
  • Microtubules (diameter 22 nm):
    • Formed from the globular protein tubulin
    • form cilia, flagella, centrioles, basal bodies
    • Important in cell division where they take a spindle form.
the endoplasmic reticulum er
The Endoplasmic Reticulum (ER)

Endoplasmic = inside the cytoplasm; Reticulum = network

  • Function
    • Plays a role in the cell’s synthetic ability: newly synthesized proteins, lipids and carbohydrates are transported within the endoplasmic reticulum’s lumen.
the er
The ER ...
  • Structure:
  • The ER consists of membranous tubules and sacs called cisternae. Membranes separate the cytosol from the internal compartment of the lumen
  • Have the same phospholipid bilayer seen in the plasma membrane
  • The ER membrane is continuous with the outer of the two membranes of the nuclear envelope
The Rough Endoplasmic reticulum (RER)
    • Occurs in cells that manufacture proteins for secretion outside of the cell (i.e digestive enzymes and hormones)
  • The Smooth Endoplasmic reticulum (SER)
    • Abounds in cells that synthesize secrete, and store carbohydrates, steroids, lipids and other non-protein products.
    • Found in testis cells; oil glands; some hormone producing gland cells; intestinal cells, where they collect products of lipid digestion; in liver cells the SER is associated with glycogen, the animal storage carbohydrate (starch).
  • Structure: Large molecular structures consisting of ribosomal rRNA sub-units and proteins.
    • Consists of 2 sub-units (large and small) which join together to form a functional ribosome only when they attach to mRNA
    • Ribosomes are constructed in the nucleolus from RNA
    • Are too large to be considered molecules. The ribsomal sub-units in prokaryotes are smaller and differ chemically.
  • Function: Where the cell assembles proteins following genetic (DNA) instructions. Ribosomes translate message from mRNA
  • There are two forms:
    • Polyribosomes or polysomes: Free
    • Bound ribosomes: Attached to the ER
the golgi apparatus
The Golgi Apparatus

Sometimes called Dyctiosomes in plant cells

  • Structure (see diagram)
    • Component of the endomembrane system
    • Made up of flattened bag-like sacs called cisternae. Found near the nucleus. (cis phase = forming face; trans face = maturing phase)
  • Function
    • Manufacturing, warehousing, sorting, and shipping center of materials in the cell
  • Structure (see diagram)
    • Have double membranes
    • Have their own circular DNA and ribosomes (make their own proteins)
    • Smaller than chloroplasts
    • develop from pre-existing mitochondria
  • Function
    • ATP (adenosine tri-phosphate) generating molecules
peroxisomes microbodies
Peroxisomes (Microbodies)
  • Structure:
    • Sacs bound by a single membrane
  • Function: (see transparency)
    • organelles found in nearly all eukaryotic cells that contain specialized enzymes for specific metabolic activities
    • All contain peroxide-producing oxidases (enzymes) that transfer H from various substrates to O producing H2O2