tissues

• Collagen synthesis


  1. Individual polypeptide of procollagen are synthesized and twisted together inside secretory vesicle

  2. Procollagen is secreted and procollagen proteinase cleaves terminal procollagen extensions

  3. Collagen molecule self assemble in fibril

  4. As you age, collagen fibrils begin to break down
• Types of cell junctions

  • Tight junctions
  • Adherens junctions
  • Desmosomes
  • Gap junctions
  • Hemidesmosomes
• tissues


  cells in highly organized communities of multicellular communities
• what are tissues made of?

  cells and extracellular matrix
• number of cells in tissues regulated by division, growth, and death
• how are plant tissues organized by?

  cell wall
• why are plant cells delicate?

  they have no intermediate filaments
• why do plant cells rely on cell wall?

  to prevent rupturing
• what is limited by the resistance of the cell wall?

  osmotic swelling
• during development, plant cells make a thin primary cell wall, then later form a secondary cell wall with more rigid/specialized properties
• what is the cell wall made of?

  cellulose microfibers
• how does the cell wall move?

  microfibers inside cell serve as track for cellulose synthase enzymes, dictating the direction of cellulose polymers
• how are animal connective tissues organized by?

  the extracellular matrix
• what is the extracellular matrix made of?

  proteins (mainly collagen) and polysacchrides
• what does collagen do?

  provides tensile strength to connective tissue
• collagen + other macromolecules = distinctive qualities to tissues
• Ehlers-Danlos syndrome is caused by a loss of proteinase that cleaves procollagen
• what do cells attach to?

  collagen fibers via fibronectin and integrin
• what does the attachments to collagen fibers allow the cell to do?

  attachments allow cell to move through a tissue
• what does the gel of polysaccharides do?

  fill in spaces between collagen
• how do the gel of polysaccharides form?

  mainly GAGs (negatively charges sugars) that draw in clouds of positive ions and water to form swollen gels
• what are cells packed into?

  epithelia sheets
• epithelia lines internal cavities and cover whole surface of body
• epithelia are polarized and rest on basal lamina
• what does formation of tissues involve?

  • cell-cell communication
  • differentiation/specialization and renewal/repair
  • cell-cell adhesion
• Tight junctions

  seal off area between cells and restrict proteins to one side
• what are tight junctions made of?

  proteins from both cells that arrange in strands along boundary
• what does tight junctions prevent?

  prevents diffusion of proteins in the membrane and also prevent solutes outsides the cell from getting through the sheet of cells
• what is an example of where tight junctions are used?

  glucose uptake in gut epithelia
• adherens junctions

  • form between cadhering proteins and tether themselves to the cytoskeleton
  • anchor cells together via their actin cytoskeleton
• what does adherens junctions also enable?

  tube formation in spinal cord development of the fetus
• desmosomes

  link cells via their intermediate filaments
• what is the function of desmosomes?

  provide strength to the epithelia sheets especially in exposed tissues (skin)
• gap junctions

  • allow cell to coordinate functions (e.g. muscle contractions)
  • allow small molecules to pass from cell to cell directly
• how are gap junctions connected?

  proteins in each cell connect to form narrow, hydrophilic tubes
• hesmidesmosomes


  anchors intermediate filaments in a cell to the basal lamina