cell bio exam 3: cell communities - extracellular matrix, cell migration

tissue can be an organized assembly of

• cells held together by cell-cell adhesion

• ECM

• cells and ECM, like connective tissue in the intestinal wall

connective tissue underlying the epithelium

• contains arrangement of cells and ECM

• mainly contains cells called fibroblast, which secretes ECM

ECM of connective tissue includes

• collagen - fibrous protein

• fibronectin

important for resisting compressive forces and carrying the mechanical load

forms of connective tissue ECM

• ECM underlying epithelium

• calcified ECM oriented in parallel or swirl patterns

• ropelike organization of tendons

• transparent substance of cornea

collagen

• stiff triple-stranded helix

  • 3 alpha chains wound around e/o

  • glycine trapped in between all of them and adhere

which molecules are important in collagen structure and how?

• glycine - spaced every third amino acid and allows the three alpha chains to be packed together

• proline - ring structure that helps stabilize helical conformation

after being secreted into extracellular space, triple-stranded collagen helices

self-assemble into polymers called collagen fibrils

collagen fibers

cable-like aggregates of collagen fibrils, which are aggregates of triplie-stranded collagen helices

• able to resist tensile forces, very strong

fibroblast cells

secrete ECM molecules through exocytosis, including collagen

inside the fibroblast, collagen is first synthesized as

a procollagen molecule with unstructured terminal peptides on either end

what do terminal peptides do to the collagen inside a fibroblast cell?

prevents the assembly into fibrils within the cell

procollagen proteinase

• extracellular enzyme

• cleaves terminal peptides off of procollagen → mature collagen

• mature collagen can self-assemble into collagen fibrils

fibroblasts can align collagen fibers by

migrating in opposite directions and tugging on fibers between them

• creates parallel bundles

• often seen in tendons, ligaments

collagen fibers in bone

• ECM is most of bone tissue

• osteoblasts (cells) are specialized types of fibroblast and are small embedded dots

• collagen fibers form striped circular bands

in bone, calcium phosphate crystals

fill the space between collagen fibers, making the bone matrix resistant to compression and tension

collagen fibrils in tadpole skin

arranged in a “plywood-like” pattern with alternating layers with different orientations/directions → resist tensile strength